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Flashcards in Final Exam Deck (360):
1

What is the “great unifying principle of biology”?

•Evolution by natural selection.

2

Provide an operationally useful definition of evolution.

•Evolution is a change in gene or allele frequencies that occurs within a species or population over time.

3

evolution always involves a …

•Genetic (heritable) variation
•Some force that can change gene or allele frequencies.

4

What is ultimate source of all genetic novelty (variation) in all populations?

•Mutations

5

What is the role of genetic recombination in the process of evolution?

•The most important source of variation upon which natural selection acts in sexually reproducing organisms because of its potential to amplify existing genetic variation.

6

Provide two points during meiosis in which genetic variation can be introduced into the genome.

•Prophase I – crossing over, double-stranded homologous chromosomes may come together and line up in synapsis. The may become linked together at various points called chiasmata.
•Anaphase I – random segregation of homologous chromosomes.

7

How can sex result in the reduction in an individual’s contribution of genes to the next generation?

•There is the loss of your own genes, since gametes contain on average only 50% of the producer’s genes.

8

What is recombinational load?

•Many individuals that result from sexual reproduction may have unfit combinations of genes and the population may have to bear this.

9

State the Hardy-Weinberg Equilibrium and explain why it is an important principle.

•In the absence of forces that change gene frequencies, in a large, randomly mating population, gene frequencies should remain the same from generation to generation.
•It may be easier to understand what causes populations to evolve if the characteristics of a population that is not evolving are considered first.
•Important because it establishes that gene frequencies do not change by themselves.

10

Define random mating.

•Possession of an allele cannot in any way influence the selection of a mate.

11

Give five forces that can lead to a change in gene or allele frequencies in a population.

• Mutation
• Gene flow
• Non-random mating
• Genetic drift
• Natural selection

12

In a closed population (one without immigration or emigration) what three forces are most likely to lead to a change in gene or allele frequencies?

• Non-random mating
• Genetic drift
• Natural selection

13

What two forces that can lead to a change in gene frequency also lead to a reduction in genetic variation within a species of population?

• Natural selection
• Genetic drift

14

What is meant by positive assortative mating?

•Individuals mate with others that are like themselves phenotypically for selected traits.

15

What is meant by negative assortative mating?

•Individuals only select mates that are phenotypically different from themselves for selected traits.

16

What is mean by consanguineous mating?

•(Inbreeding) Mating with close relatives, which is an extreme form of positive assortative mating.

17

What problems can arise from consanguineous mating?

•Offspring expected to have many alleles in common.
•Inbreeding results in significantly less genetic diversity among the descendants than if outbreeding had occurred.
•Harmful alleles are more likely to appear if present, the result of which is a reduction in fitness called inbreeding depression.

18

What is sexual selection?

•Mode of natural selection (and non-random mating) in which some individuals reproduce more than others because they are better sexual selection.

19

Define the term genetic drift.

•Genetic drift involves random changes in gene frequency that occur in small populations due to sampling error.
•Always leads to a reduction in genetic variability within a population as alleles are lost or fixed.

20

In what type of population is genetic drift most likely to be a force that can lead to a change in gene or allele frequencies?

•Small populations

21

What is meant by the term “genetic bottleneck” and what are its consequences to a population or species?

•When a species experiences a drastic decline in a population as a result of a natural disaster or over hunting.
•Since there may be only a few individuals left in such a population to contribute their genes to the next generation a population bottleneck may result in a dramatic change in allele frequencies as well as significant reduction in genetic variability.
•Population bottleneck is when a few individuals may contribute genes to the entire future population of the species.

22

Genetic drift may also be important when a few individuals emigrate and begin a new population, a phenomenon known as the __________________.

• Founder effect.

23

Define natural selection.

•Differential reproduction, where certain genotypes in the population leave more offspring to the next generation than others.
•Results in a reduction in genetic variation within a species or population

24

What is stabilizing selection?

•If the environment is stable, then extreme phenotypes may be selected against. (birth weights)

25

What effect does stabilizing selection have on phenotypic variation in a population?

•Tends to reduce phenotypic variation and counter the effects of mutation, genetic drift and gene flow from other populations.
•Does not lead to a change in the mean values of traits.

26

What is directional selection? Give a possible example of directional selection in nature.

•Selection may act against one extreme phenotype in favor of the other.
•Over time allele frequencies shift in a steady constant direction.
•EX: Evolution of long necks in giraffes.

27

What is disruptive selection? What is the possible outcome of disruptive selection?

•If the environment is heterogeneous enough, selection may favor forms at both ends of the phenotypic range, and intermediate forms are selected against.
•This may result in the development of two different phenotypes, that is, a genetic polymorphism.

28

What is the difference between a transient polymorphism and a balanced polymorphism?

•Transient: if the frequencies of the alleles or phenotypes changes over time.
•Balanced: The frequencies of two or more alleles or phenotypes remains relatively stable over time.

29

Provide three ways in which a balanced polymorphism might be maintained.

•Neutral alleles – individuals with these alleles do not differ in their fitness.
•Heterozygous advantage – heterozygote is favored
•Environmental heterogeneity – one phenotype might be favored during winter, the other during summer or in different habitats.

30

Give an example of a balanced polymorphism thought to be maintained by heterozygote advantage.

•Heterozygous advantage is when the heterozygote is favored by selection. Both alleles will be maintained in the population, even if they may lower the fitness of their owners in the homozygous state.
•Ex: persistence of sick cell anemia in parts of Africa.

31

What type of adaptation is seen in the evolution of melanism in peppered moths in UK?

• Transient polymorphism: if the frequencies of the alleles or phenotypes changes over time.

32

Define the term “fitness”. What range of values can W assume? How is fitness calculated?

•Fitness is a measure of the number of offspring left by an individual (genotype) relative to the ideal (reference) genotype in the population.
•W must range between zero and one
•What ever is most fit is 1.00. The next one you divide the two values.
oDark is 0.50 and Light is 0.25.
W for dark is 1.00 while W for light is 0.50

33

Give three reasons why organism may not be perfectly adapted.

•Availability of adaptive genes
•Opposing selection pressures
•Environmental change

34

What is the “Red Queen Hypothesis”?

•Organisms may have to keep making evolutionary changes just to survive in the face of such deteriorating conditions.
•Has also been proposed to explain the origin and value of sexual reproduction and the almost unlimited genetic variation that it can provide in a population of sexually reproducing organisms.

35

Under most circumstances, what is the target of selection?

• Individuals

36

What are altruistic traits and how might they be selected for?

•Traits that help other members of your group, which may be the result of kin selection.
•If you help genetically related individuals, you may still be passing on copies of your genes.

37

How should natural selection affect two species that are potential competitors?

•The competitor with the greater fitness has more offspring.

38

What is the first step in the process of allopatric speciation?

•Population fragmented by a barrier into two or more subpopulations.

39

Provide two of the most likely ways in which populations separated by a barrier might diverge genetically.

• Natural selection (selection pressures)
• Genetic drift

40

Define adaptive radiation and give a possible example of adaptive radiation in nature.

•Generation of a number of different forms from a basic stock.
•Ex: evolution of the Galapagos finches if a flock got blown off course and colonized different islands and the birds adapted to its different environments and led to the evolution of different species.

41

Define adaptive radiation and give a possible example of adaptive radiation in nature.

•Generation of a number of different forms from a basic stock.
•Ex: evolution of the Galapagos finches if a flock got blown off course and colonized different islands and the birds adapted to its different environments and led to the evolution of different species.

42

Complete this sentence: According to Ernst Mayr, biological species are…

•Group of interbreeding organisms reproductively isolated from other such groups.

43

Provide a definition for reproductive isolating mechanisms.

•Intrinsic (biological) properties of an organism that prevent them from interbreeding with other species.

44

Are rivers, canyons, mountain ranges, etc. considered reproductive isolating mechanisms? If not, why not?

•No, because they are intrinsic properties, that is, found within the organism itself.

45

How can premating (prezygotic) reproductive isolating mechanisms be improved by natural selection?

•By selection against less fit hybrids.
•Such mechanisms are the most efficient because they prevent the loss of an individual’s genes.

46

What is meant by behavioral isolation?

• Such things as having different mating calls and courtship patterns.

47

What is meant by temporal isolation?

• Breeding at different times.

48

What is meant by ecological isolation?

• Breeding in different habitats.

49

What is meant by mechanical isolation?

• Reproductive parts don’t fit together.

50

What is mean by gametic isolation?

• Many marine species that broadcast gametes into the water column have recognition proteins on the gametes that only allow fertilization by individuals of the same species.

51

Give an example of a postmating isolating mechanism.

• Hybrid sterility in mules

52

What is the probable function and meaning of biological species?

•Through reproduction isolation, species serve to preserve coadapted gene complexes, that is, they allow species to become adapted to their own ecological niches.

53

How has an “evo-devo” approach to studying the process of evolution changed previously held views that differences among species are due solely to differences in their genes?

•Evolutionary and developmental biology is a field of biology that compares the developmental processes of different organisms to determine the ancestral relationship between them and to discover how developmental processes evolved.
•Much biodiversity is not due to differences in genes, but rather to alterations in gene regulation. In other words, great differences among organisms may not be due to differences in their genes but rather in the way their genes are regulated and expressed.

54

What happened in the 1980s when the algal species Caulerpa taxifolia was introduced into the Mediterranean Sea.?

•It had never occurred in colder waters, nor in such densities
•Caulerpa produces secondary compounds that deter fish and invertebrate herbivores
•Caulerpa spread quickly ‒ French marine biologists calculated its rate of spread at 1 hectare in 5 years!

55

What is species richness?

•to count or list the species that are present

56

What kinds of problems are associated with measures of species richness?

•counting all the species in a community is essentially impossible, especially if small or unknown species…are considered.
•In practice, however, this is an extremely difficult thing to do, partly because of taxonomic problems and also because of…sampling problems. That is, how do you know for sure when you have found all of the species in the community?

57

Provide three ways in which subsets of species be defined.

•Taxonomic affinity (e.g. all bird species in a community)
•Guild ‒ group of species that use the same resources
•Functional group ‒ species that function in similar ways

58

What are some of the problems of characterizing communities in terms of food webs?

•food webs tell little about the strength of interactions or their importance in the community
•Some species span two trophic levels, and some change feeding status as they mature
•Some species are omnivores, feeding on more than one…trophic level
•Idealized food webs often do not include important elements such as symbionts and detritivores
•All organisms that die without being consumed become organic matter (detritus) and can be consumed by detritivores (mostly fungi and bacteria) through a process known as…decomposition.
•Food webs do not include nontrophic (horizontal interactions) such as competition)!

59

What are interaction webs and how do they describe both trophic (vertical) and non-trophic (horizontal) interactions in a community more accurately?

•Interaction webs more accurately describe both trophic (vertical) and non-trophic (horizontal) interactions
•Food webs do not include nontrophic (horizontal interactions) such as competition)!

60

What does species evenness measure?

•species richness tells us nothing about the relative abundance of individuals among the species that make up the community
•Measures of evenness provide this information, with the maximum possible evenness occurring when each species….is equally represented.

61

Under what conditions is species evenness maximized?

•Such measures increase as the numbers of individuals in the total population are more evenly distributed…among the species.

62

What are species diversity indices?

•Measures of species diversity (called diversity indices) have been devised that take into account both species richness and evenness

63

What kinds of communities have the greatest species diversity indices?

•Such measures increase as the numbers of individuals in the total population are more evenly distributed…among the species.
•Intuitively a community dominated by one or two species is less diverse than a community with the same numbers of species, each of which is well represented

64

How is biodiversity different from species diversity?

•Species diversity (and biodiversity) are often used more broadly to mean the number of species in a community
•Biodiversity describes diversity at multiple spatial scales, from genes to species to communities
•Implicit is the inter-connectedness of all the components!

65

What are rank abundances curves and what can they tell you?

•Rank abundance curves plot the proportional abundance of each species (pi) relative to the…others in rank order.
•Relative abundances can suggest what species interactions might be occurring.
•In one community, a dominant species might have a strong negative effect on other rare species

66

What are species accumulation curves and what do they tell you?

•Species accumulation curves plot richness as a function of total number of…individuals counted.
•These curves can help determine when most or all of the species in a community have been observed

67

What are some examples of direct interactions?

•Direct interactions are those that occur between two species (e.g. competition, predation, etc.)

68

How do indirect interactions different from direct interactions?

•Direct interactions are those that occur between two species (e.g. competition, predation, etc.)
•With indirect interactions, the relationship between two species is mediated by a….third (or more) species.
•Indirect effects are often discovered by accident when species are experimentally removed to study the strength of direct interactions.

69

What are trophic cascades?

•Trophic cascades occur when predators in a food web suppress the abundance or alter the behavior of their prey, thereby releasing the next lower trophic level from predation (or herbivory if the intermediatetrophic level is a herbivore).
•A carnivore eats an herbivore (a direct negative effect on the herbivore)
•The decrease in herbivore abundance has a positive effect on a primary producer
•In kelp forests, sea otters feed on sea urchins, which feed on the kelp
•Thus, sea otters have a positive indirect effect on…kelp.
•Kelp, in turn, can positively affect abundance of other seaweeds, which serve as habitat and food for marine invertebrates and fishes.

70

How do sea otters have a positive effect indirect on kelp forests?

•In kelp forests, sea otters feed on sea urchins, which feed on the kelp
•Thus, sea otters have a positive indirect effect on…kelp.

71

What are some of the benefits of kelp forests to other organisms in the sea?

•Kelp, in turn, can positively affect abundance of other seaweeds, which serve as habitat and food for marine invertebrates and fishes.

72

What is trophic facilitation?


•Trophic facilitation involves a condition in which a consumer is indirectly facilitated by a positive interaction between its prey and another species

73

Give some examples of trophic facilitations in nature.

•scavenging is a widespread behavior and an important process influencing food webs and…ecological communities.
•Large carnivores facilitate the movement of energy across trophic levels through the scavenging and decomposition of their killed prey
• Carrion is an essential but temporal resource for countless species ranging from microbes to…vertebrates.
•Interactions between salt marsh plants that affect aphid abundance

74

In what types of environments are trophic facilitations more likely to occur?

•trophic facilitation is more likely to occur in physically stressful environments than in favorable environments, where competition may be the most important interaction among species

75

What service does the rush Juncus provide for marsh elders (Iva)?

•Juncus and a Iva (a genus of wind-pollinated plants in the daisy family known generally as marsh elders) have a commensalistic relationship
•Juncus shades the soil surface, decreasing evaporation and salt buildup
•Juncus also has a type of tissue that allows oxygen…roots
•Some oxygen moves into the soil where other plants can use it

76

What effect does Juncus growth have on aphid growth in salt marshes?

•Experimental removal of Juncus decreased the growth rate of Iva, but removing Iva had no effect on Juncus!
•But population growth rates of aphids on marsh elders were significantly higher when Juncus was present
•So, Juncus has both positive and negative effects on the marsh elder (it improves soil conditions, but also facilitates the aphids)
•But since marsh elders cannot survive indefinitely without Juncus, the positive effects outweigh the negative effects of the…increased aphids.

77

How do competitive networks differ from linear hierarchical systems?

•In a competitive network, as opposed to a linear hierarchical system, no one species dominates the interaction, allowing for…coexistence.
•Competitive networks consist of interactions among multiple species in which every species has a negative effect on every other species

78

What does interaction strength refer to?

•Interaction strength refers to the magnitude of the effect of one species on the abundance of another species

79

How is interactions strength measured?

•It is measured by removing one species (the interactor species) from the community and observing the effect on the other species (the target species)

80

Give an example of how interaction strengths may depend on environmental factors.

•Menge et al. (1996) measured interaction strength of sea star (Pisaster) predation on mussels (Mytilus) in wave-exposed versus wave-protected areas
•Interaction strength was greater in protected areas
•Pisaster was a less efficient predator when exposed to…crashing waves.

81

What are ecosystem engineers?

•Many foundation species are ecosystem engineers, that is, they create, modify, or maintain physical habitat for themselves and other species

82

Give some examples of ecosystem engineers.

•Corals build coral reefs that many other species use
•Kelp forests (formed by brown algae) provide shelter and suitable habitat for numerous other organisms in…marine ecosystems.

83

What is a dominant species?

•The dominant species in a community is the species that is present in the greatest numbers, in other words, the species with the largest…population in the community.

84

What are keystone species?

•A keystone species is a species that has a disproportionately large effect on its environment relative to…its abundance.
•Such species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and numbers of various other species in the community
•Keystone species usually influence community structure indirectly, via trophic means, as in the case of sea otters and kelp forests

85

Give an example of a keystone species that is also an ecosystem engineer.

•Beavers ‒ a few individuals can have a large impact by building dams. Dams can transform a swiftly flowing stream into a marsh with…wetland plants.
•At the landscape level, beavers can create a mosaic of wetlands within a larger forest community, which increases regional biodiversity

86

What is meant by “redundant species”?

•having the same function as other species within a larger…functional group.

87

What is meant by some species interactions being context-dependent?

•changeable under different environmental conditions

88

What are some of the effects of increasing water temperatures on corals in the Indian Ocean?

•coral bleaching (loss of symbiotic algae)
•If the algae do not return, the corals die, creating conditions for species replacement
•Rising sea level can decrease light for corals and their symbionts, leading to replacement by…low-light tolerant species.

89

What effect does increased ocean acidification have on coral exoskeletons?

•Increasing ocean acidification can dissolve the skeletons of corals

90

In what ways might biotic agents of change lead to changes in community structure over time?

•Biotic interactions can result in replacement of one species with another
•Diseases can initiate community change by causing death or slow growth of a species
•Ecosystem engineers or keystone species can influence community change

91

Explain the concept of a closed community.

•kind of superorganism whose species were tightly bound together
•Thus viewed, the community would be seen as a discontinuous assemblage of species with…sharp boundaries.

92

Explain the concept of an open, or individualistic view of community organization.

•Seeing the relationship of coexisting species as simply the results of similarities in their requirements and tolerances and partly the result of chance
•In this view, community boundaries would be continuous (not sharp)

93

Under what conditions are the discontinuities between communities fairly well defined?

•usually they are found where there are sharp physical boundaries such as the aquatic-terrestrial transition
•Or where there are very different soil types

94

How did Charles Elton view the process of succession?

•Elton believed that organisms and the environment interact to…shape succession.
•Elton emphasized that the only way to predict the trajectory of succession was to understand the biological and environmental context in which it occurred!
•Elton also recognized the contribution of animals to succession.
•He showed how animals, by eating, dispersing, trampling, and destroying vegetation could greatly influence the sequence and…timing of succession.

95

Describe the process of degradative succession and give an example of such a successional pattern.

•occurs over a relatively short time scale when a packet of dead material is exploited by decomposers and detritivores
•Ultimately, degradative succession ends when the resource is…completely used up

96

Describe the process of allogenic succession and give an example of such a successional pattern.

•involves the serial replacements of species that occur as a result of changing geophysical and chemical forces, that is, they are driven by external forces
•For example, the conversion of salt marshes…into woodlands.

97

Distinguish between primary and secondary autogenic succession and give examples of each type.

•Primary production: The establishment and development of plant communities in newly formed habitats previously without plants is called primary succession
-Examples: the primary succession that occurs on exposed till left by glaciers in southeast Alaska, Mosses and shallow-rooted herbaceous species are the first colonizers. These are replaced by several kinds of willows, which are replaced by alders that come in and produce thickets with a scattering of cottonwood. The alders are invaded by Sitka spruce, forming a dense mixed forest which continues to develop as western and mountain hemlock become established.
•Secondary succession: The return of an area to its natural vegetation following a major disturbance is called secondary succession.
-Examples: plowed fields in the eastern United States were abandoned by farmers moving west after the frontier was opened up in the 19th century that it has been called…old field succession. The pattern of succession starts with annual weeds that are replaced by herbaceous perennials, which are then replaced by shrubs and then by light-loving successional trees. And finally, by shade-tolerant species.

98

What are the most common “pioneer organisms” in the process of primary succession and what is their role in this process?

•Lichens are often the pioneer organisms of primary succession on bare rock, beginning the chemical breakdown necessary for the formation of soil.

99

What is hydrarch succession?

•Hydrarch succession occurs in aquatic habitats as lakes fill in with organic matter
•The typical sequence of events is from pond to marsh or swamp, followed by the conversion of moist forest to…dry upland forest.

100

What is the facilitation model of successional dynamics?

•In this model (inspired by the closed community model), species replacement is facilitated by previous stages that make modifications in the abiotic environment
•Eventually, the final invaders modify the habitat in a way that prevents the establishment of any further colonizers (i.e. a climax community)

101

What is the tolerance model of successional dynamics?

•This model also assumes earliest species modify the environment, but in neutral ways that neither benefit nor inhibit later species
•The sequences of succession are thus entirely dependent on life-history characteristics such as the specific amount of energy a species allocates to growth

102

State the inhibition model of successional dynamics

•This model assumes early species modify conditions in negative ways that hinder later successional species
•In this model, species replacement is inhibited by the residents until they are damaged or killed
•The only possibility for new growth/colonization in this successional sequence arises when a disturbance leads to dominating species being destroyed, damaged or...removed.

103

How does the replacement of species occur in the inhibition model of successional dynamics?

•In this model, species replacement is inhibited by the residents until they are damaged or killed
•The only possibility for new growth/colonization in this successional sequence arises when a disturbance leads to dominating species being destroyed, damaged or...removed.

104

How did Sousa (1979) test the inhibition model of successional dynamics?

•Sousa (1979) studied algae growing on boulders in the intertidal zone of the California coast
•Bare substrates are colonized rapidly by a pioneer green algae.
•The tougher, long-lived red algal species cannot colonize the area until the green algae are killed by wave action or selective grazing by a crab species that feeds only on the green algae

105

Explain Tilman’s resource-ration hypothesis of successional dynamics.

•Places strong emphasis on the role of changing competitive abilities of plant species as conditions slowly…change with time.
•He argues that species dominance at any point in a terrestrial succession is strongly influenced by the relative availability of two resources - a limiting soil nutrient (often nitrogen) and light
•Early in succession, the habitat experienced by seedlings has low nutrient levels but high light availability
•As the result of litter input and the activities of decomposer organisms, nutrient availability…increases with time.
•Total plant biomass also increases with time, which means that less light reaches the soil surface
• Thus, pioneer species are those that tolerate low nutrient levels but need high light levels, such as shorter shrubs
• Later species need more nutrients but can tolerate shade…such as taller trees.
•Tilman accepts that many other factors may also influence the course of succession, including differences in colonizing ability growth rates and response to grazing

106

Why is the concept of scale important to ecological investigations?

•Thus, the exact nature of a community is determined by the dynamic processes of deaths, replacements and micro-successions that a broad view might…conceal.
•And the characteristics of a community emerge from the interaction of a hierarchy of processes acting over different scales of time and space
•Thus, ecological studies of communities must look at regional and historical processes as well as local, contemporary ones!

107

Define standing crop and how it is measured?

•Standing Crop consists of the bodies of living organisms within a given area, which consists of a certain amount of biomass

108

Define biomass and how it is measured.

•actual mass of organisms per unit area, which is usually expressed in units of energy, such as joules/m2 or dry organic matter, such as tons/hectare

109

Define gross primary productivity and how it is measured.

• total fixation of energy by photosynthesis, a portion of which is lost as…respiratory heat (R)

110

Define net primary productivity and how it is measured.

•Net primary productivity (NPP), which is the difference between GPP and R
-actual rate of production of new biomass that is available for consumption by heterotrophic organisms, that is, bacteria, fungi and animals

111

Define secondary productivity and how it is measured.

•rate of biomass produced by such…heterotrophs

112

What are some of the most productive ecosystems on Earth?

•swamps, marshes and estuaries
• algal beds, coral reefs and cultivated fields

113

What are some of the least productive ecosystems on Earth?

deserts, open oceans

114

Compare the productivity to biomass (P:B) ratios for forests, other terrestrial ecosystems and aquatic ecosystems.

•Forests: very low (0.042)
•Grasslands and shrublands: intermediate (0.29)
•Aquatic: high (17.0)

115

Why do P:B ratios decrease during succession?

•Early pioneers are rapidly growing herbaceous species with relatively little support tissue and later…woody vegetation.

116

What role do sunlight, water and temperature play in determining the primary productivity in a community?

•Sunlight may be limiting even under the brightest conditions, for many leaves of a plant may actually be in relative shade. Furthermore, much of this solar radiation is unavailable for use by plants
•Water is often limiting, since large quantities of water may be lost by evapotranspiration because the stomates must remain open for much of the time for CO2 to be taken in
•Temperature can influence productivity in a complex fashion. Increasing temperature leads to higher rates of net photosynthesis but only up to the point at which loss by an exponentially increasing respiration rate is greater. Water loss also increases with temperature.

117

What is potential evapotranspiration and how is it important in predicting patterns of primary productivity?

•Potential evapotranspiration refers the theoretical maximum rate at which water might evaporate into the atmosphere under the prevailing conditions.
•Potential evapotranspiration minus precipitation provides a crude index of the availability of water for growing vegetation
•On a global scale, such an index clearly identifies water deficit as a major factor in…low productivity.

118

Give two factors that determine how much light is intercepted by a forest canopy.

•Because of an incomplete canopy, much of incident radiation lands on the ground instead of on the leaves
•This could be because of seasonality in leaf production and shedding or because of defoliation by grazing animals, pests and diseases.

119

Distinguish between autochthonous and allochthonous material and the importance of each for still and running waters.

•Autochthonous: In aquatic communities organic matter (and fixed energy) generated within the community. Most of this input is through photosynthesis by large plants and attached algae in shallow waters and by microscopic plankton in the open water.
•Allochthonous: energetic resources may come into aquatic communities as dead organic material (detritus) that has been produced outside it! Material arrives in rivers or is blown in by wind.
•For example, a stream running through a wooded watershed derives almost all of its energy input from litter shed by the surrounding vegetation since shading from trees prevents any significant growth of photosynthetically…active organisms.
•Allochthonous inputs can be very important in stream ecosystems. For Example: Bear Brook in New Hampshire receives 99.8% of its energy as allochthonous inputs! In nearby Mirror Lake, autochthonous energy accounts for almost 80% of the energy budget!

120

How does the river continuum concept relate to the importance of autochthonous and allochthonous energy inputs from the headwaters toward the lower reaches of a river.

•The river continuum concept states that the importance of autochthonous energy inputs increases from the headwaters toward the lower reaches of a river
•Water velocity decreases and nutrient concentrations increase as you go downstream
•Whereas, in a large lake (or the ocean) the organic inputs may be due almost entirely to photosynthesis by…phytoplankton

121

What are the sources of nutrient inputs into lakes and marine ecosystems?

•Lakes receive nutrients by the weathering of rocks and soils of their basins, in rainfall and as the result of human activity, such as fertilizers and…sewage input.
•In oceans, nutrient inputs may come from estuaries in continental shelf regions or from upwellings of nutrient-rich waters from the bottom where nutrients accumulate by sedimentation

122

Define euphotic zone

•depth within which net photosynthesis is positive

123

Define compensation point

•the depth at which gross primary productivity is just balanced by…respiration.

124

Define Secchi depth

• One way to measure the clarity of the water is to lower a black and white disk on a calibrated line and note the exact depth at which it disappears

125

What key factor influences the depth of the euphotic zone in aquatic ecosystems?

• clarity of the water and anything that reduces visibility reduces primary productivity

126

Compare and contrast a food chain with a food web.

•Food chain: energy is through a linear series of energy exchanges at different…trophic levels.
•Food web: diets that include more than one type of food, more complex.

127

Explain the difference between top-down and bottom-up control of ecosystem energetics.

•Top-down control refers to situations in which the structure (i.e. abundance, number of species, productivity, etc.) of the lower trophic levels depends on the effect of consumers (predators) from higher trophic levels
•Bottom-up control refers to ecosystems in which the nutrient supply, productivity and type of primary producers (plants and phytoplankton) control the structure of the ecosystem. That is, control of community structure depends on factors such as nutrient concentration and prey availability that influence a trophic level…from below. In other words, populations at this trophic level are controlled primarily by competition not predation!

128

Give an example of an ecosystem thought to be controlled by top-down mechanisms.

•occurs in marine ecosystems dominated by kelp forests, which are comprised of several species of large…sea weeds
•In such ecosystems, sea otters are the most important predators because they prey on sea urchins, which in turn eat the kelp
•When the sea otters are removed, the sea urchin populations grow and overgraze the kelp forest, which eventually leads to sea urchin barrens!
•In other words, such ecosystems are not controlled by producers (the productivity of the kelp) but rather by a…top predator.

129

Give an example of an ecosystem thought to be controlled by bottom-up mechanisms.

•An example of bottom-up control would be how plankton populations are controlled by the availability of nutrients
• Plankton populations tend to be higher and more complex in areas where ocean upwelling brings nutrients to the…surface

130

Under what conditions do trophic cascades occur?

•Trophic cascades occur when predators in a food web suppress the abundance of their prey, thereby releasing the next lower trophic level from predation or herbivory if the intermediate trophic level is an herbivore

131

Why are trophic cascades thought to be more common in aquatic ecosystems than terrestrial ones?

•Trophic cascades are thought to be more common in aquatic ecosystems than terrestrial ones, since terrestrial ecosystems may have more…complex food webs.

132

Give a couple of examples aquatic trophic cascades.

•For example, if the abundance of large fish-eating fish is increased in a lake, the abundance the smaller fish prey that feed on zooplankton may also decrease, which may allow the zooplankton population to increase, leading to a decrease in…phytoplankton biomass.
•In the Eel River, in Northern California, fish (steelhead and roach) consume fish larvae and predatory insects. These smaller predators prey on midge larvae, which feed on algae. Removal of the larger fish increases the abundance of…algae.
•In Pacific kelp forests, sea otters feed on sea urchins. In areas where sea otters have been hunted to extinction, sea urchins increase in abundance and kelp populations…are reduced.

133

What happened when brown trout were introduced to New Zealand in the 1860s?

•Brown trout reduced total invertebrate density more than the galaxias did.
•Algal abundance also increased more with brown trout present.
•Thus, in this trophic cascade: brown trout had a greater effect on primary production than native fish did!

134

Describe the trophic cascade that may have been caused by the reintroduction of gray wolves (Canis lupus) into Yellowstone National Park in 1995 and 1996.

•Since then a three-tiered trophic cascade has been reestablished involving wolves, elk (Cervus elaphus) and woody browse species such as aspen (Populus tremuloides), cottonwoods (Populus spp.) and willows (Salix spp.).
•Mechanisms likely include wolf predation on elk, which reduces their numbers and the threat of predation.
•Which, in turn, alters elk behavior and feeding habits, resulting in these plant species being released from intensive…browsing pressure.

135

What are riparian communities, and how might they have been affected by the reintroduction of the wolves in Yellowstone National Park?

•Those that border rivers and streams
•wolf predation on elk, reduce their numbers and the threat of predation. Which, in turn, alters elk behavior and feeding habits, resulting in these plant species being released from intensive…browsing pressure

136

According to Hairston, Smith and Slobodkin (1960), what limits carnivores, herbivores and plants?

•Carnivores severely exploit their resources and are limited by competition with each other
•Since herbivores are being regulated by carnivores, they do not compete strongly and have little impact on the…vegetation.
•The relatively little exploited plant populations are therefore limited by strong competition for resources such as light, water and nutrients

137

How does the HSS hypothesis explain “why the world is green”?

•The relatively little exploited plant populations are therefore limited by strong competition for resources such as light, water and nutrients

138

Provide some examples of habitats that may not “be green” and give the reasons for these exceptions.

•steppe and tundra habitats whose greenness is maintained for only a few weeks
•habitats where there is a severe shortage of forage during the unfavorable season, when herbivores may have a heavy impact on…available territory

139

Give three other criticisms of the HSS hypothesis.

•(1) Plants possess numerous defenses against herbivory, and these defenses also contribute to reducing the impact of herbivores on plant populations
•(2) Herbivore populations may be limited by factors other than food or predation, such as nesting sites or…complex food webs
•(3) For trophic cascades to be ubiquitous, communities must generally act as food chains, with discrete trophic levels

140

Distinguish between primary producers, primary consumers and secondary consumers.

•Primary producers: first trophic level, autotrophs, form the base of all food chains and food webs, generates most of the dead organic matter in an ecosystem (plants, algae, cyanobacteria)
•Primary consumers: second trophic level, herbivores, cannot manufacture their own food and must derive their energy by consuming producers directly (grasshoppers, ground squirrels, caterpillar, rabbits, prairie dogs, bison, deer)
•Secondary consumers: primary carnivores, heterotrophs can obtain their energy indirectly by eating herbivores and other organisms that feed on producers (scorpion, birds, detrivores, bobcats, mountain lions, wolves, hawks, owls)

141

Give three reasons for the existence of ecological pyramids and two important consequences of such ecological pyramids.

•Existence: the loss of energy that occurs at each trophic level results in ecological pyramids.
o1. much of what is produced dies without being grazed.
o2. not all of the biomass ingested is assimilated
o3. The second law of thermodynamics dictates that some energy will inevitably be lost during energy transfer.
•Consequences:
o1. There is a limit to how many higher trophic levels can be supported by the size of the producer base.
o2.Biomagnification – the concentration of persistent toxins in the bodies of organisms occupying higher trophic levels.

142

What is meant by the description of food webs as “static descriptions of energy flow and trophic interactions”?

•As more organisms are added to a food web, complexity increases to reflect the complexity of real ecosystems.
•feeding relationships can span multiple trophic levels (omnivory) and may even include cannibalism!

143

In what ways may food webs be more dynamic?

•Some organisms change feeding patterns over their lifetime.
•Some animals, such as migratory birds, are components of multiple food webs.
•Most food webs do not include other types of interactions, such as pollination.
•The role of microorganisms is often ignored, despite their processing of a substantial amount of the…energy

144

What do interaction strengths in food webs measure?

•Interaction strength is a measure of the effect of one species on the population size of another species.

145

Why did Paine (1966) call the sea star Pisaster a keystone species?

•Paine called Pisaster a keystone species (predator), having a greater influence than its abundance or biomass would predict!

146

How might a keystone species lead to greater species diversity in a community?

keystone species may be critical for protecting the many other species that…depend on it.

147

The potential for indirect effects to offset or reinforce the direct effect of a predator should be greatest when the direct effect is weak. How was this idea tested by Berlow (1999) using predatory whelks, mussels, and acorn barnacles?

•Whelks have a direct negative effect on mussels by eating them.
•Barnacles facilitate mussels by providing crevices for mussel larvae to settle in.
•But when barnacle density is high, they do not attach well and are easily knocked off the rocks, along with the…mussel larvae.
•When barnacles are at low densities, whelk predation on barnacles has a negative indirect effect on mussels by removing the mussel substrate.
• But when barnacles are at high densities, thinning by whelks has a positive indirect effect on mussels by providing them with a more stable…settlement substrate.

148

What are the factors that allow naturally complex food webs to be stable?

•How an ecosystem responds to species loss or gain is strongly related to the stability of food webs
•weak interactions can stabilize trophic interactions.
•some natural food webs may have a particular organization that allows increased species diversity to have a…stabilizing effect.
•the buffering influence of weak interactions and behavioral or evolutionary changes in prey choice can help reduce population fluctuations associated with complex food webs
•The identity of species in the web is also important! For example, some species (like keystone species) exert a disproportionally greater influence on stability, while others are more likely to extinct!

149

What is the relationship between plant production and more diverse communities?

•Plant production is often higher in more diverse communities, and more diverse plant communities are better able to recover from…disturbances.

150

Give an example of a study where the community of all herbivores showed greater stability with increasing plant diversity.

•In general, arthropod communities were more stable in plots with higher plant diversity

151

What is the “The Portfolio Effect’” and how do causes natural systems to be more stable when they are more diverse?

•The portfolio effect is a phrase that ecologists use to describe why it is that more diverse systems seem to be more stable
•And so one thing that happens (because nature always has good and bad years for different species) is that if you have many species growing together and you average their responses, the average of that more diverse portfolio in nature is more stable.

152

What are compensatory interactions and how do causes natural systems to be more stable when they are diverse.

•When one species’ abundance declines, another species is freed from competition with that species, and the population size of that species can increase

153

Give some examples of some organisms do not conveniently fit into trophic levels.

•Omnivores feed at multiple trophic levels.
•Example: Coyotes are opportunistic feeders, consuming vegetation, mice, other carnivores and even old leather boots!

154

In terrestrial ecosystems, only a small portion of the biomass is actually consumed; what happens to the rest of it?

•most of the energy flow passes through as…detritus

155

What is meant by trophic efficiency?

•Trophic efficiency refers to the way in which energy is passed around the levels of a food web.

156

Give three reasons why is so much energy, biomass, or number of individuals lost in going from one trophic level to the next?

(1) Much of what is produced dies without being grazed, supporting a decomposer community of bacteria, fungi and…detrivores
(2) Not all of the biomass ingested is assimilated, and some of it is lost in feces, which also becomes available to decomposers
(3) The Second Law of Thermodynamics dictates that some energy will inevitably be lost during…all energy transfers

157

What are transfer efficiencies?

•The proportion of primary productivity flowing along each of the possible energy pathways depends on the way energy is used and passed on from one trophic level to the next!

158

What is meant by consumption efficiency and why are they typically low for most communities?

•Consumption efficiency refers to the percentage of total productivity available at one trophic level that is actually consumed
•These values are typically low, partly because much of what is out there is not good to eat, as well as the fact that herbivore densities are…low in many habitats

159

Are consumption efficiencies higher in aquatic ecosystems than in terrestrial ecosystems? Higher for carnivores than herbivores?

•Consumption efficiency is higher in aquatic ecosystems than in terrestrial ecosystems.
•Consumption efficiencies also tend to be higher for carnivores than for herbivores.

160

What is meant by assimilation efficiency?

•the percentage of food taken in the guts of consumers that is actually assimilated across the gut wall The remainder is lost as feces, which become available to decomposers

161

How does food quality affect assimilation efficiencies?

•Assimilation efficiency is determined by food quality and the physiology of the consumer!
•Food quality of plants and detritus is low because of complex compounds such as cellulose, lignins and humic acids, which are not easily digested and low concentrations of nutrients such as nitrogen and phosphorus
•Animals have carbon-to-nutrient ratios similar to the animals consuming them

162

How do some herbivores have higher assimilation efficiencies than expected when so much of their diet includes cellulose?

•Ruminants (cattle, deer, camels) have a modified foregut with bacteria and protists that break down cellulose.

163

What is meant by production efficiencies?

•Production efficiency refers to the percentage of assimilated energy that is incorporated into…new biomass
•The remainder is lost to the community as respiratory heat
•Production efficiency is strongly related to the thermal physiology and…size of the consumer.

164

Why are production efficiencies so low for endotherms?

•Endotherms allocate more energy to heat production and have less for growth and reproduction than ectotherms

165

How does body size affect production efficiencies in endotherms? Why?

•Body size affects heat loss in endotherms.
•As body size increases, the surface area-to-volume ratio…decreases

166

How might the number of trophic levels change in a community?

•The number of trophic levels may change due to addition or loss of a top predator or a predator in the middle of the food chain.
•Or, an omnivore may change…food preference.

167

What kind of factors may control the number of trophic levels in a community?

•Amount of energy entering via primary production: More production should allow more trophic level. This appears to be important in…resource-poor ecosystems.
•Nutritional content of autotrophs, detritus and prey and the efficiency of energy transfers: Herbivores on land consume a much lower proportion of autotroph biomass than herbivores in most aquatic ecosystems.

168

What kind of evidence suggests that herbivore production is limited by the amount of food available?

•There is a positive relationship between net primary production and amount of biomass consumed by herbivores

169

Provide three reasons why terrestrial herbivores don’t consume more of the available biomass?

(1) Herbivores are constrained by predators and never reach…carrying capacity.
(2) Autotrophs have defenses against herbivory, such as secondary compounds, spines, etc.
(3) Phytoplankton are more nutritious for herbivores than terrestrial plants.

170

How might the frequency of disturbance affect the number of trophic levels in a community?

•Higher trophic levels depend on lower levels and take time to re-establish after disturbance.
•If disturbance is too frequent, higher levels may never…become established.

171

How might ecosystem size affect the species diversity of a community?

•Larger ecosystems support larger populations, have more habitat heterogeneity, and have higher species diversity.

172

Cite a study that demonstrated that larger sized ecosystems have higher species diversity.

•A study of 36 islands in the Bahamas found that island size was correlated with number of trophic levels (Takimoto et al. 2008).
•Disturbance frequency did not impact trophic levels, but the top predator species…changed

173

What are “ecological pyramids” and what causes them?

•The loss of energy (about 90%) that occurs at each trophic level usually results in what Elton (1927) called ecological pyramids
•That is, pyramids of numbers, biomass or productivity!

174

What is biomagnification and why does it occur?

•Ecological pyramids also result in a problem called biomagnification, the concentration of persistent toxins (i.e. ones that are not broken down or metabolized) in the bodies of organisms occupying…higher trophic levels.

175

Give an example of the effects of biomagnification.

•On herring gulls: Shells too thin to incubate (crack)
•On humans: DDT in some mother’s milk is found in levels higher than that allowed by EPA for cow’s milk!

176

What is bioaccumulation and how does it differ from biomagnification?

•Relates to the concentration of toxins in the bodies of living organisms within a trophic level
•Bioaccumulation refers to the increase in concentration of a substance in certain tissues of organisms' bodies due to absorption from food and the environment over time
•Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the…substance is lost.
•Difference: bioaccumulation is when the one species absorbs a toxin over time. Biomagnification is when a species consumers other species with toxins giving them the toxins.

177

Give an example of bioaccumulation and its effects on humans.

•Fish and shellfish concentrate mercury in their bodies, often in the form of methyl mercury, a highly toxic organic compound of mercury
•The presence of methyl mercury in fish and shell fish can be a particularly serious health issue for women who are or may become pregnant, nursing mothers and…young children

178

Who was Rachel Carson and what was the title of the book she wrote?

•The dangers of bioaccumulation and biomagnification of DDT and other persistent toxins were publicized by Rachel Carson in Silent Spring (1962).
•She described the devastating effects of pesticides, especially DDT, on nontarget bird and…mammals species.

179

How did this book contribute to the conservation movement and eventual ban on DDT in the United States?

•Rachel Carson’s careful documentation and ability to communicate with the public led to increased scrutiny of chemical pesticides and eventually a ban on manufacture and use of DDT in the United States!
• And her book Silent Spring has to be considered one of the most important books on biological conservation, ushering in an “Era of Doubt” about the…use of pesticides.

180

What is the intermediate disturbance hypothesis?

•Connell (1978) proposed that communities which experience intermediate levels of disturbance will maintain the highest species diversity!
•At higher levels of disturbance, gaps will not progress beyond the pioneer stage and overall species diversity will be…lower.
•While at too low a frequency, competitive exclusion will reduce overall diversity!

181

How did Sousa (1979) test this hypothesis?

•Sousa worked with boulders of differing size classes (small, medium, large) which because of their size were overturned (disturbed) with high, intermediate and low frequency respectively
• Consistent with the Connell's hypothesis, boulders of intermediate size, and therefore disturbance maintained the highest level of community…species diversity.

182

How might the intensity of predation affect species diversity ion a community?

•Too little predation may allow dominant species to competitively exclude weaker species from the community
•And too much predation may drive the preferred prey…toward extinction.

183

Explain Huston’s Dynamic Equilibrium Model and how it differs from Connell’s (1978) Intermediate Disturbance Hypothesis.

•Huston (1979) added competitive displacement to the intermediate disturbance model
•According to this model, the best competitor uses the limiting resources, reducing the weaker competitor’s population growth to the point of extinction, which is just another way of saying…competitive exclusion.
•Huston’s dynamic equilibrium model combines disturbance frequency and rate of competitive displacement to determine species diversity

184

According to Huston’s dynamic equilibrium model under what conditions will maximum species diversity in a community be achieved?

•It predicts maximum species diversity will occur when disturbance level and rate of competitive displacement are equal and are at…intermediate levels.

185

Why do Menge and Sutherland (1987) argue that predation should NOT be considered the same as disturbance?

•Menge and Sutherland (1987) argue that because predation is a biological interaction, it should be considered separately!

186

What do Menge and Sutherland (1987) propose is the role of stress in ordering natural communities?

•They argued for a central role of environmental…stress

187

What does Menge and Sutherland's model predict is the relationship between predation and stress?

•With complexity inversely related to environmental stress
•Their model predicts that predation is most important when environmental stress is low
•As stress increases, importance of predation decreases and competition increases in importance
•At high stress levels, neither is important!

188

How do Menge and Sutherland (1987) incorporate recruitment into their model and how do they view the relationship between competition and recruitment

•If recruitment is low, competition might not be important because resources would not be limiting
•As recruitment increases, competition becomes…more important.

189

How might disturbance theory be integrated with ecological management policies?

-As we have seen, disruptions that prevent species assemblages from reaching any highly ordered state are common
• In fact, most communities probably exist at some level of non-equilibrium, held in that state by…environmental disturbances.
•Armed with this knowledge, ecologists can use non-equilibrium theory to suggest ways in which communities might be manipulated to desired ends
•Such as for conservation, agriculture, forestry and wildlife management
• Most importantly, we now recognize that in order to preserve biodiversity natural disturbances should…not be prevented.

190

What are Lottery & Neutral Models and how do they relate to community structure?

•The above models assume an underlying competitive hierarchy
•Lottery models and neutral models emphasize the role of chance in maintaining community species diversity
•In lottery models, all species have equal chances of obtaining resources that were made available by disturbances, and this allows coexistence

191

Under what conditions do lottery and neutral models most likely explain community structure?

•The lottery model may be most relevant in very diverse communities where many species overlap in their resource requirements
•Its relevance decreases in communities in which species have large differences in interaction strength!

192

How does “membership” in a community depend on the regional species pool and dispersal?

•The regional species pool provides an upper limit on the number and types of species that can be present in a community.

193

How does “membership” in a community depend on abiotic conditions?

•A species may be able to get to a community but be unable to tolerate the…abiotic conditions
•Climate change may facilitate invasive species that would not have survived colder temperatures.

194

How does “membership” in a community depend on species interactions?

•Coexistence with other species is also required for community membership
• Other species may be required for growth, reproduction, or survival
•Species may be excluded by competition, predation, parasitism or…disease.

195

What factors may account for differences in patterns of productivity of terrestrial organisms over the Earth?

•For example, in general, productivity decreases from the tropics to the poles and with…increasing altitude.
•These decreases must (in part) reflect decreases in solar radiation, mean temperatures and length of the growing season

196

What is the relationship between productivity and depth in aquatic environments and why?

•In aquatic environments, productivity declines with depth as temperature and light levels fall

197

Do patterns of productivity in animal communities track those plant communities?

•In general, the productivity of animal communities follows the same trends

198

Under what conditions might an increase in productivity lead to an increase in species richness?

•Increased productivity might lead to increased species richness if it leads to an increased range of…avaible resources.

199

What relationship did Pianka (1967) find between lizard diversity in the deserts of the southwest and length of growing season?

•Pianka (1967) found a positive relationship between species richness of lizard communities in the deserts of the southwest and length of the growing season

200

What relationship did Brown and Gibson (1983) find between the diversity of cladoceran zooplankton and total productivity in eleven unpolluted lakes in Indiana?

•Brown & Gibson (1983) demonstrated that the diversity of cladoceran zooplankton in 11 unpolluted Indiana lakes was positively correlated with total productivity of those lakes
•But it may not! - Increased productivity could instead lead to more individuals per species rather than…more species.

201

What did the same authors observe in the three polluted lakes they studied?

•Brown & Gibson (1983) noted a low species diversity of zoo plankton in three polluted Indiana lakes!
•And there are a number of studies that suggest the greatest species diversity occurs at intermediate levels of…productivity

202

What is the “Paradox of Enrichment” and how might you account for it?

•the increase in productivity typically seen in the cultural eutrophication of aquatic systems usually leads to lower…species diversity.

203

What did relationship did Abramsky and Roseznweig (1983) observe between species diversity of desert rodents in Israel and precipitation?

•Abramsky and Roseznweig (1983) found highest species diversity of desert rodents in Israel at intermediate levels of precipitation, an…index of productivity.
• Thus, it seems that when increased productivity is accompanied by an increased range of resources, an increase in species richness should follow

204

How might precipitation serve as an index of productivity?

•it seems that when increased productivity is accompanied by an increased range of resources, an increase in species richness should follow
•intermediate levels of precipitation result in high species diversity therefore high productivity.

205

How might environmental disturbances lead to an increase in species richness?

•When disturbances open up gaps, and the community is dominance controlled such that strong competitors replace…weaker ones
•Thus, in such cases, it may be the frequency of the disturbances that determines community…species richness.

206

Why might there be an initial increase in species richness when disturbances open up gaps?

•There may be an initial increase in species richness as a result of colonization of the newly-created gaps

207

Why might there be a later decline in species richness in such habitats that experience disturbances

•decline in richness due to competitive exclusion

208

How might the frequency and intensity of disturbances affect the species richness of a community?

•Thus, in such cases, it may be the frequency of the disturbances that determines community…species richness.
•Intermediate levels of disturbance maintain community richness.

209

What is does the “Intermediate Disturbance Hypothesis” predict?

•the highest levels of community richness will be maintained at intermediate levels of disturbance

210

How might a predator increase community species richness?

•predator-mediated coexistence may lead to an increase in species richness

211

How might intense predation lead to a reduction in species richness of a community?

•Intense predation pressure may reduce richness by driving prey species (whether or not they are strong competitors) to…extinction.

212

How might intermediate levels of predation promote the greatest species richness?

•For example, in a study of the effects of cows and oxen on a grassland community in Ethiopia
• The researchers (Mwendera et al. 1997) found that the greatest number of plant species was maintained at intermediate levels of…grazing
•At ungrazed plots, several highly competitive plant species accounted for 75-90 percent of the ground cover
•At intermediate levels of grazing, the cattle kept the aggressive, competitively dominant grasses in check, thus allowing the greatest number of plant…species to persist.
•But a very high levels of grazing, plant species richness declined as the cattle were forced to turn from heavily grazed preferred plant species to less preferred species, driving some to extinction
•Where grazing pressure was particularly intense, only a few grazing-tolerant species were…able to persist.

213

Why might structurally more complex environments accommodate extra species?

•Environments that are more structurally complex might support more species because they provide a greater variety of microhabitats and microclimates
• And perhaps more types of places (refuges) to…hide from predators.

214

How might predictable, seasonally changing environments support higher species diversities?

-In a predictable, seasonally changing environment, different species may be suited to the conditions at different…times of the year.
- Thus, seasonal environments may provide more opportunities for temporal niche differentiation, which can ultimately lead to higher species diversity
.

215

How might a stable environment support more species? How might it not support more species?

•Stable environments might be expected to support more species because there may be more opportunities for…specialization
•Such environments might be able to support specialized species that would not persist where conditions or resources fluctuate dramatically!
•On the other hand, one could argue that populations in stable environments are more likely to reach their carrying capacities and experience greater competition, leading to…competitive exclusion

216

How might you characterize an environmentally harsh habitat?

•Although harshness may not be easy to define, it does appear that environments requiring energetically costly morphological or biochemical adaptations that are not found in related species support fewer species than more benign ones

217

What are some of the problems associated with attributing low species diversity of some habitats with environmental harshness?

•The problem with many examples, however, is that many of the so called harsh environments are characterized by other features associated with low species richness
• For example, many are unproductive, perhaps as a consequence of the harshness
• And most have low spatial heterogeneity
•Furthermore, many occupy small areas such as caves, hot springs and mountain tops and thus may be seen as small…isolated islands.

218

What is the “evolutionary time” hypothesis for explaining differences in patterns of species diversity?

•Evolution takes time, and some communities may show low species richness because of insufficient time for re-colonization or for subsequent evolution after a major…disturbance.

219

How might the evolutionary time hypothesis be used to explain the difference in temperate tree species diversity between Europe and North America?

•The same argument can be applied to many areas of the Earth, particularly temperate regions that have been subjected to recent glacial activity
•Which may not yet have reached their potential equilibrium…species richness.
•For example, the low species richness of temperate forest trees in Europe compared to North America has been attributed to the fact that the major mountain ranges in Europe run east to west, whereas in North America they run north to south!
•When the glaciers advanced south, the trees in Europe were trapped against the mountains becoming extinct, whereas in North America, they simply…retreated southward.
•Thus, there may not have been sufficient evolutionary time for the European trees to recover to their equilibrium richness
•In fact, even in North America is it likely that equilibrium has not been regained because of the slow rate of post-glacial spread of displaced species.

220

What is the general pattern for latitudinal species gradients?

•The most widely recognized pattern in species diversity is the decrease in diversity that occurs from the tropics to the poles (as well as that

221

What is the general pattern for altitudinal species gradients?

•high altitude communities usually occupy smaller, more isolated areas than lowlands at equivalent latitudes
•And thus, they represent islands with the expected decrease in species richness that accompanies such habitats

222

What is biogeography?

•the study of distribution of living organisms and the reasons for those distributions

223

Who is the “father of biogeography”?

• Alfred Russel Wallace

224

Who is the co-author of the theory of evolution by natural selection?

• Alfred Russel Wallace and Darwin

225

Wallace’s Line pass passes through two islands in what country?

• Bali and Lombok in Indonesia.

226

What are Wallace’s six biogeographic regions (realms) and where are they located

(1) Nearctic (North America & Greenland)
(2) Neo-Tropical (South America)
(3) Ethiopian (Africa)
(4) Palearctic (Most of Northern Asia)
(5) Oriental (Most of Southern Asia)
(6) Australasian (Australia & New Zealand)

227

Describe the process of seafloor spreading.

•At mid-ocean ridges, molten rock flows from the seams between plates and cools, creating new crust and forcing the plates to move apart

228

What are some of the results of subduction zones of the continental plates?

•one plate is forced downward under another plate, resulting in earthquakes, volcanic activity and the formation of…mountains.
•In other places, the plates slide sideways past each other, forming a fault.

229

About 250 million years ago all the land masses on the Earth were joined in a “supercontinent” named _________.

• Pangaea

230

After that, the “supercontinent” split into what two land masses?

• Pangaea split into Laurasia to the north and Gondwana to the south.

231

After that Gondwana split into what present-day regions of the Earth?

• Gondwana separated into present-day South America, Africa, India, Antarctica and… Australia.

232

Laurasia then split into what regions of the Earth?

• Laurasia split up into North America, Europe and…Asia

233

North America was originally part of ______________, while South America was part of _______________.

• Laurasia, Gondwana

234

The Nearctic and Palearctic were both part of ancient________________.

• Laurasia

235

What is vicariance and what causes it?

• Vicariance refers to the evolutionary separation of species by barriers such as those formed by continental drift (i.e. long-term processes).

236

How can the legacy of continental drift can explain the distribution of extant and fossil ratites?

• The legacy of continental drift can be found in the fossil record and in existing taxonomic groups such as the large flightless birds (ratites) had a common ancestor from…Gondwana.

237

Provide another well documented example of vicariance involving the formation of the Isthmus of Panama.

•Another well-documented example of vicariance in the marine realm was the formation of the Isthmus of Panama about 3 million years ago, which resulted in the evolution of related species pairs on the…Atlantic and Pacific sides

238

From an ecological perspective, what is an island?

•An island can be any kind of isolated area surrounded by…unsuitable habitat.
•As such, lakes are islands surrounded by land, southwestern mountain tops are islands surrounded by a sea of desert and fallen fruits, trees and dung heaps are all islands!
•Habitat fragments, such as in the Amazon forest, can be considered as islands.
•All display the same basic pattern: large islands contain more species than small islands!

239

What is the species-area curve, and what does it describe?

•The relationship between habitat area and species richness is called the species-area curve
•In general, larger areas contain more species than smaller ones of...similar habitat.

240

What does a comparison of species-area curve for islands and comparable pieces of mainland reveal about species richness and the slope of a curve relating number of species to area? Why?

•(1) Islands usually contain fewer species. That is, they have a lower value for the intercept on the S-axis of the species-area graph. This is especially true for species occupying higher… trophic levels
•(2) The species-area relationships for islands are on average steeper than those for mainland areas, that is, the slope of the line relating number of species to area is…steeper.

241

Describe the habitat diversity theory for explaining patterns of island biogeography and some of the factors it fails to consider.

•Probably the most obvious reason larger islands contain more species is that they typically have more diverse habitat types
•While this may be true to some extent, it cannot account for all aspects of island patterns
•For example, it fails to consider the dispersal capabilities of the organisms themselves
•It also fails to consider changes that take place within island biotas over…evolutionary time

242

The following questions relate to the Equilibrium Theory of island biogeography: What factors determine the number of species found on an island?

•the number of species on an island will be determined by a dynamic balance between immigration and…extinction.

243

The following questions relate to the Equilibrium Theory of island biogeography: At what point does the colonization curve fall to zero?

•the rate of immigration of new species to an island should decrease as the number of species increases
•Since eventually all species from the “species pool” (potential colonizers from source areas surrounding the island) will reach the island and the immigration rate will…drop to zero.

244

The following questions relate to the Equilibrium Theory of island biogeography: Why should rates of extinction on islands increase as species richness increases?

•Because of competitive exclusion!
• And because smaller populations may be more vulnerable to…chance extinctions.

245

The following questions relate to the Equilibrium Theory of island biogeography: Why does the theory predict a dynamic equilibrium and what does this mean?

•when the rate of immigration equals the rate of extinction, a dynamic equilibrium of species richness is reached
•Although species richness stays constant, the continual turnover of species means that the actual species composition of the island can be and that the equilibrium will be a dynamic one!

246

The following questions relate to the Equilibrium Theory of island biogeography: What factors determine the shape of the immigration and extinction curves?

•The shape of the immigration and extinction curves determines the actual equilibrium point
•Because dispersal falls off more or less exponentially with distance, rates of immigration should decrease with increasing distance from…source areas.
•Also (to some extent) with decreasing island size since smaller islands present smaller “targets” for colonizers
•Although extinction rates should be unaffected by distance from the source areas, they should be higher for smaller islands because of increased competitive exclusion and smaller…population sizes.

247

The following questions relate to the Equilibrium Theory of island biogeography: What types of islands does the model predict will have the greatest number of species?

•the largest number of species should be found on large islands that are close to the…mainland supply areas.

248

The following questions relate to the Equilibrium Theory of island biogeography: What types of islands does the model predict will have the fewest number of species?

•Species number should decline with increasing remoteness of an island

249

The following questions relate to the Equilibrium Theory of island biogeography: Give two reasons why smaller islands are likely to have fewer species than larger ones.

•island is a true isolate, whereas a similar sized patch of mainland habitat is…only a sample.
•Species that exist on an island must find all of conditions necessary to support them
•Rare species can occur in the mainland sample both due to migration from other areas
•The species-area relationships for islands are on average steeper than those for mainland areas
•This difference arises again because islands represent true isolates
•If they are small, then they may be harder to get to, that is, they present smaller “targets” for…colonization.
•more likely to have higher extinction rates due to competitive exclusion and a lower availability of resources and habitats

250

The following questions relate to the Equilibrium Theory of island biogeography: What aspect of the equilibrium theory is unique?

•The prediction of an equilibrium number of species as a result of species turnover, is truly unique to the MacArthur Wilson theory of island biogeography!
• dynamic

251

What is meant by the indeterminacy of island communities?

•there is a significant degree of chance regarding exactly which species are present in the community

252

Why do island communities often show patterns of disharmony in their species assemblages and what are the effects of such disharmony?

•This disharmony occurs partially because of differences in powers of dispersal
•Species may also differ in their susceptibility to extinction (low density species like predators)
•Species dependence on the prior arrival of some other species (parasites, predators)

253

According evolutionary theory, how might rates of speciation on remote islands compare with rates of colonization?

•On oceanic (remote) islands, rates of speciation may be comparable with or even faster than rates of…colonization.

254

Why do islands often show high degrees of species endemism?

•high degree of endemism (the occurrence of species found nowhere else) on islands reflects the influence of evolution in these isolated communities
•Recall that the first step in geographic speciation is always…physical isolation.

255

According to evolutionary theory, why might some remote island communities not be “saturated”?

•some island communities may not be “saturated” simply because there has been insufficient time for the evolution of all of the potential species!

256

Describe the SLOSS (single large or several large) debate and how might be important to the design of wildlife refuges.

•The important question is, if a given amount of habitat is to be set aside for a wildlife reserve, should it be a single large reserve or several small ones?
•Diamond (1973) argued that one large park was better than several smaller ones because extinction rates go up as park size goes down
•But Simberloff and Abele (1976) argued from the species area curve that several smaller reserves might contain more species than one large one
•If each of the small reserves supported the same species, then it would be preferable to construct the larger reserve and thus, conserve more species
•But Dobson and May (1986) point out that many scattered reserves would be less susceptible to the ravages of an epidemic disease than a single larger one
• Moreover, if the region as a whole is heterogeneous, then each of the small reserves may support a different group of species, and the total number conserved might exceed that of a…single large reserve.
•A number of studies suggest that many small islands may support more species than a comparable area of one or a few large islands
•Often, however, conservation efforts are directed at low density species that can only be supported by large areas
• In such cases, a single large area may be the only way to accomplish this goal!
•Since some extinctions in island reserves are inevitable, it is important to insure that immigration is possible
•This can be done by careful arrangement of scattered reserves or by providing corridors or stepping-stones of natural habitat…between them.

257

What are riparian corridors and what is their importance to wildlife conservation?

•land that borders rivers and streams
•provide such immigration routes for some species
•they are also some of the most biologically diverse…terrestrial habitats.
•As such, sound riparian management can help to ameliorate (lessen) the impact of many ecological problems related to land use and environmental quality

258

What is approximate concentration of carbon dioxide in the Earth’s atmosphere today?

• 400 ppm

259

What are two problems with clearing tropical forests by burning with respect to atmospheric carbon dioxide levels?

• Which not only increases the load of CO2 but also reduces the uptake of CO2 …by plants

260

What is the greatest contributor of carbon dioxide to atmospheric carbon dioxide levels?

• And CO2 is exchanged with the atmosphere mostly by photosynthesis and respiration

261

Although about half of the anthropogenic CO2 is taken up by the oceans and terrestrial biota why will this proportion decrease over time?

• But this proportion will decrease because terrestrial and ocean uptake will not keep pace with the rate of…atmospheric increase

262

Although forests may be an important sink for anthropogenic CO2, why might they less capacity to do this in the future?

• Older forests, or ones with less nutrients and water, may not have as great a capacity for CO2 uptake

263

What effect does the absorption of increased atmospheric CO2 have on the ocean?

•Atmospheric CO2 also affects ocean pH by diffusing in and forming…carbonic acid.
•Ocean acidity has increased 30% over the last century

264

How will ocean acidification affect many marine organisms that produce calcium carbonate shells?

•Many marine organisms form shells of calcium carbonate
•Increasing acidity will dissolve existing shells, and lower calcium carbonate concentrations will decrease the ability to synthesize…new shells.

265

How might this acidification affect the formation of coral reefs?

•On Australia’s Great Barrier Reef, calcium carbonate formation declined by 14% from 1990 to 2009
• Anthropogenic CO2 emissions therefore have potential to tremendously alter the diversity and function of… marine ecosystems.

266

Provide four sources of increased atmospheric methane levels:

(1) Burning fossil fuels
(2) Agricultural development (primarily rice grown in flooded fields)
(3) Burning of forests and crops
(4) Livestock production

267

Describe the process of nitrogen fixation.

•Fixation converts gaseous nitrogen (N2) to ammonia and nitrates

268

What are the two main sources of fixed nitrogen?

•Ammonia produced by biological fixation contributes about 90% of the fixed nitrogen contributed to the Earth each year. (organisms like bacteria)
•While the remainder comes from nitrates produced by…lightning.

269

What organisms are responsible for nitrogen fixation?

•mutualistic bacteria living in association with the…legumes.
•Well-known legumes include alfalfa, clover, peas, beans and peanuts!
•A large number of nonleguminous plants (many of them pioneering species that grow on sites where soil nitrogen is low) also have nitrogen fixing…root nodules.

270

What are the main nitrogen fixers in Asian rice paddies?

• Free-living soil bacteria and cyanobacteria (the main nitrogen fixers in Asian rice paddies) also contribute to pool of fixed nitrogen available to plants

271

Describe the process of mineralization (ammonification) of organic nitrogen.

•In this energy-yielding process, proteins and nucleic acids in dead plant and animal tissue are broken down by bacteria and fungi to…amino acids.
•The amino acids are then oxidized to carbon dioxide, water and ammonia
•Which is absorbed directly by plant roots and incorporated into organic molecules to be passed through the…food chain.

272

Describe the process of nitrification, indicating the organisms involved in this process.

•Nitrification is another energy-yielding process in which ammonia is oxidized to nitrite (NO2–) and finally to nitrates (NO3–1) by two groups of organisms
•Nitrosomonas bacteria use ammonia in the soil as their sole source of energy, oxidizing it first to nitrous acid and water and then to nitrite (NO2–)
•Energy left in the nitrite ion is then exploited by the Nitrobacter bacteria, which oxidize the nitrite ion to…nitrate.

273

Describe the process of denitrification and under what conditions it occurs.

•Denitrification occurs when some of these nitrates are reduced to gaseous nitrogen by certain fungi and bacteria to obtain oxygen!
•These organisms are facultative anerobes, preferring an oxygenated environment
•But if no oxygen is present, they can use nitrate instead as a hydrogen acceptor, with the release of nitrogen gas as a…by product.

274

What human activities contribute to nitrogen losses and gains?

•Losses in nitrogen occur through the conversion of forests and grasslands to…croplands.
•Loss: Mixing and breaking up the soil exposes more organic matter to rapid decomposition
•Loss: Removal of nitrogen through harvesting crops, grazing and timber harvesting cause additional losses
•Gain: Heavy applications of fertilizer disrupt natural balances between fixation and…denitrification
•Gain: Excessive amounts of nitrates from fertilizers, animal wastes in feedlots and human wastes may find their way into surface and ground water supplies, endangering the health of aquatic organisms as well as…humans

275

What are some of the problems associated with excessive amounts of nitrogen being added to ecosystems?

•Excessive amounts of nitrates from fertilizers, animal wastes in feedlots and human wastes may find their way into surface and ground water supplies, endangering the health of aquatic organisms as well as…humans

276

How can excessive amounts of nitrates from fertilizers, animal wastes in feedlots and human wastes endanger the health of aquatic organisms as well as humans?

•Nitrates may get into surface and ground water supplies.
•Excess nitrate and nitrite can cause methemoglobinemia, which decreases the ability of the blood to transport oxygen!” Hypoxia

277

How might increased levels of fixed nitrogen being introduced into aquatic ecosystems affect those ecosystems?

•Human waste (treated or otherwise) add even heavier nitrogen loads to rivers, lakes and estuaries, contributing to cultural eutrophication and oxygen depletion of these habitats!

278

What are ocean “dead zones” and what causes them?

•Anoxic conditions over large areas are called “dead zones”
•increased export of nitrogen to nearshore marine ecosystems contributes to eutrophication and oxygen depletion

279

Why might plants living in nutrient poor environments not respond to increased nitrogen levels?

•In nutrient-poor environments, many plants have adaptations that lower their nutrient requirements, which lowers their capacity to take up excess nitrogen

280

What might happen to such plants if their environment is enriched with fixed nitrogen?

•Faster-growing species may then outcompete them, resulting in loss of biodiversity and change in…community composition.

281

Of the 20 factors that Stevens et al. (2004) studied in a survey of grasslands in Great Britain, which factor explained the most variation? What was their conclusion about increased nitrogen deposition?

•Of 20 factors that may have influenced species richness, nitrogen deposition rate explained the most variation
•Higher nitrogen inputs were associated with lower…species richness.

282

What are the major sources of nitrogen oxides in the atmosphere?

•Automobiles and power plants are the major sources of nitrogenous pollutants in the atmosphere, particularly nitrogen oxides

283

What is the principal nitrogenous pollutant in the atmosphere and what are its effects on humans?

•However, the primary nitrogenous pollutant is nitrogen dioxide (NO2), a pungent gas that is the main component of… smog.
•In significant concentrations it is highly toxic, causing serious lung damage (especially in children) with a delayed effect.

284

What happens to nitrogen dioxide in the atmosphere when it is reduced by ultraviolet radiation?

• Becomes smog.`

285

What environmental problem does the addition of nitric oxide to the atmosphere cause?

• Some of these nitrogen oxides are quickly converted into nitric acid (HNO3), which falls as acid precipitation

286

What are two serious environmental problems caused by the release of nitrous oxide (N2O) into the Earth’s atmosphere?

•This gas is now the dominant ozone-depleting substance emitted by humans – and is likely to remain so throughout the century!
•nitrous oxide is biggest threat to the Earth's ozone layer and possibly the biggest contributor in the future to…Global warming.

287

What are chlorofluorocarbons (CFCs) and what threat do they pose to life on Earth?

•Human-produced chemicals called chloro-fluorocarbons
•they were eating a hole in the ozone layer above Earth’s polar regions

288

What is the Montreal Protocol and what was it designed to do?

An international treaty called the Montreal Protocol regulated production of CFCs and certain other ozone-depleting gases in 1987

289

What are some natural sources of nitrous oxide emissions?

•microorganisms such as bacteria and fungi in…soils and oceans.
•Soils under natural vegetation are an important source of nitrous oxide, accounting for 60% of all naturally produced emissions
•Other natural sources include the oceans (35%) and atmospheric chemical reactions (5%)

290

What are some anthropogenic sources of nitrous oxide emissions?

- Fertilized agricultural soils and livestock manure (42%)
- Runoff and leaching of fertilizers (25%)
- Biomass burning (10%)
- Fossil fuel combustion and industrial processes (10%)
- Biological degradation of other nitrogen-containing atmospheric emissions (9%)
- Human sewage (5%)

291

What is the effect of soil cultivation, the use of nitrogen fertilizers and animal waste handling on naturally occurring bacteria with respect to nitrous oxide production?

•These activities stimulate naturally occurring bacteria to…produce more nitrous oxide.

292

List three factors dictate how much a greenhouse gas contributes to global warming:

(1) Their ability to absorb heat (their Global Warming Potential)
(2) How long they stay in the atmosphere (also known as their "lifetime").
(3) Their concentration in the atmosphere

293

List five four important greenhouse gases found in the atmosphere.

• Carbon dioxide
• Methane
• Nitrous oxide
• Fluorinated gases

294

How is the Global Warming Potential (GWP) of greenhouse gases defined?

•Global Warming Potential (GWP) is a measure created by the EPA
•Specifically, it is a measure of how much energy the emissions of 1 ton of a gas will absorb over a given period of time, relative to the emissions of 1 ton of carbon dioxide (CO2)

295

What is the GWP of carbon dioxide?

•CO2, by definition, has a GWP of 1 regardless of the time period used, because it is the gas being used as the reference

296

List some of the major sources of atmospheric methane emissions.

• The major sources of atmospheric methane are ruminant animals and microbial decomposition in swamps, marshes and tundra and industrial gases

297

What is the troposphere?

• The troposphere is the lowest portion of Earth's atmosphere

298

Although the quantity of methane released into the atmosphere is very small in comparison to the amount of carbon dioxide, why is there so much concern about increased methane emissions?

•even though methane is the second most abundant greenhouse gas being emitted into the atmosphere, it is up to 80 times more effective at trapping long wave radiation than…carbon dioxide.
• The GWP methane (28–36 over 100 years) also takes into account some indirect effects, such as the fact that it is a precursor to ozone, which is also greenhouse gas in the…trophosphere.

299

What are to major problems caused by nitrous oxide emissions?

•leading cause of the destruction of the Earth’s ozone layer
•Nitrous Oxide (N2O) has a GWP 265–310 times higher than that of CO2 for a 100-year timescale!

300

Which greenhouse gas has the highest GWP?

• Nitrous oxide

301

Why is there concern over the release of fluorinated gases even though they constitute a small fraction of total greenhouse emissions?

•Many fluorinated gases have very high global warming potentials (GWPs) relative to other greenhouse gases, so small atmospheric concentrations can have large effects on global temperatures
•They can also have long atmospheric lifetimes, in some cases lasting thousands of years!
• And in general, fluorinated gases are the most potent and longest lasting type of greenhouse gases emitted by…human activities.

302

Provide two ways in which global warming causes rising sea levels.

• melting ice caps and the expansion of the warmer…sea waters.

303

What are some other possible consequences of global warming?

•problems for marine ecosystems we have seen the result from the warming of oceans
Increases in the ranges of disease carrying vectors that require warmer temperatures!
• Increased frequency and magnitude of hazardous weather (i.e. hurricanes, tornados, droughts, floods, heat waves, etc.)
• And increased desertification of once productive…croplands.

304

What might a 1.1° to 4.8°C change in temperature mean for alpine communities?

• The median value (2.9°C) would correspond to a 500 m shift in elevation
• In the Rocky Mountains, this would correspond to a shift from subalpine forest (spruce and fir) down to montane forest of Ponderosa pine
• result in an elevational shift in vegetation zones of 200 ‒ 860 m

305

What might such a change in temperature do to communities with respect to latitude?

• movement of communities 500 ‒ 1,000 km toward the poles

306

Are most plants and animals expected to be able to adapt to rapid climate changes? If not, why not?

• Because climate change will be rapid, most plants and animals will not be able to respond with…evolutionary change.

307

If plants cannot adapt to rapid changes in climate, what are their options for avoiding extinction?

• Dispersal may be the only way to avoid extinction, but dispersal barriers and habitat fragmentation will be important constraints.

308

What kind of barriers to dispersal can prevent migration of many kinds of organisms?

• Dams, habitat fragmentation

309

What kind of ecosystem processes might be affected by climate change?

• decomposition, nutrient cycling and…Net Primary Productivity.

310

How might migratory animals be affected by climate change?

• Fish and whales may have to make longer journeys to find prey
• Birds arrive earlier in spring, but plants and invertebrates they depend on for food may not be available at the…same time.

311

Which regions of the globe are experiencing greater warming?

• And some regions have seen greater warming, especially mid- to high latitudes in the…Northern Hemisphere.

312

What are some of the effects of global warming on precipitation and what areas have been affected the most?

• Precipitation in the high latitudes of the Northern Hemisphere has also increased, but the weather has been drier in the subtropics and…tropics.

313

Give three ways in which sulfur is released into the atmosphere naturally?

• formation of sea-spray aerosols
• volcanic eruptions
• activities of sulfate-reducing bacteria.

314

What human activity contributes about the same amount of sulphur into the atmosphere each year?

• burning of fossil fuels (coal and oil) releases about the same amount of sulphur into the atmosphere as sulfur dioxide (SO2)

315

What happens to sulphur dioxide released into the atmosphere by human activities and what environmental problems does it cause?

• The sulfur dioxide released is oxidized and converted to sulfuric acid in microscopic aerosol droplets, which fall in rain, snow or fog

316

What is acid precipitation and what causes it? How might the rapid spring melting of snowfall containing oxides of sulphur and nitrogen cause problems for aquatic ecosystems?

• the input of human caused sulphur dioxide and nitrogen oxides is responsible for an environmental problem called… acid precipitation.
• snowfall accumulates over the winter and melts quickly in the spring, discharging a huge pulse of acidic waters into rivers and lakes.

317

How does pH affect the concentration of aluminum ions in aquatic ecosystems and what might this do to aquatic organisms?

• lead to an increase in concentration of aluminum ions in the water, which may have a more toxic effect than the increased acidity itself!
• Such pulses of acid water may be particularly damaging to amphibians that breed in temporary pools and flooded sites, contributing to their widespread declines

318

How does a drop in pH in aquatic ecosystems affect the activities of bacterial decomposers in the sediments, and in turn, aquatic and terrestrial food chains?

• Acidification of lakes also reduces bacterial activity in sediments, inhibiting decomposition and…nutrient regeneration.
• Which can limit the production of phytoplankton and invertebrate populations upon which fish depend for food
•And such acid rain has been blamed on the extinction of fish population in thousands of lakes, particularly in northern Europe and eastern North America.
• The loss of fish can, in turn, lead to a reduction and survival among many fish eating birds such as…herons and loons.
• Substantial leaching of nutrients on acidic soils can reduce…nutrient availability.

319

What are some of the effects of acid precipitation on terrestrial ecosystems?

• Substantial leaching of nutrients on acidic soils can reduce…nutrient availability.
• Acid rainfall can inhibit the activity of fungi and bacteria in the soil, reducing humus production, mineralization and fixation of nutrients
• Vulnerability of organisms depends on the acid neutralizing capacity of their ecosystem.
• As H+ percolates through soil, it replaces Ca2+, Mg2+ and K+ at cation exchange sites on clay particles
• These cations then leach out of the root zone, and the soil becomes acidic
• This decreases nutrient supplies and increases in…toxic metals.
• Aluminum is toxic to plants, soil invertebrates and aquatic organisms

320

What are some of the effects of acid precipitation on needle-leafed conifers?

• Needle-leafed conifers are particularly effective at removing moisture from the air, which means that they also take in and concentrate whatever pollutants the moisture contains!
• Mortality
• Damaged leaves
• Limit nutrients available to them
• Poisoning

321

How can acid precipitation affect the cation exchange sites on clay particles?

• As H+ percolates through soil, it replaces Ca2+, Mg2+ and K+ at cation exchange sites on clay particles
• These cations then leach out of the root zone, and the soil becomes acidic

322

Why is the phosphorus cycle referred to as a sedimentary cycle?

• because of the general tendency for mineral phosphorus to be carried from the land to the oceans, where it will be eventually incorporated in the sediments

323

How is phosphorus released from the lithosphere?

• The phosphorus in aquatic systems is lost to the sediments, but is cycled again with tectonic uplift and…weathering of rocks.

324

What human activities contribute phosphorus to aquatic ecosystems?

• Phosphate applied as fertilizer
• Wastes from food-processing plants and feed lots.
• Sewage treatment plants.

325

Which of these activities makes the greatest contribution of phosphorus to aquatic ecosystems?

• Sewage treatment plants.
• This phosphorous comes from human waste as well as phosphate containing detergents.

326

What is meant by cultural eutrophication and what are its consequences for aquatic ecosystems?

• human-caused caused nutrient enrichment of aquatic ecosystems.
• Addition of phosphates and nitrates.
• Increased phosphorus and nitrogen cause blooms of phytoplankton and cyanobacteria, which in turn leads to increased turbidity and loss of large aquatic plants
• the decomposition of this increased biomass places a substantial biological oxygen demand on these ecosystems. Which results in waters with little aesthetic appeal as well as low oxygen concentrations that cause invertebrate and… fish kills.

327

Why is nitrogen often a limiting factor for plants even though it is the most abundant component of the Earth’s atmosphere?

it must be 1st chemically converted to a usable form, "fixed" N2 to ammonia and nitrates

328

What is the primary biological role of oxygen and why?

• Its primary biological role in such oxidation is that of an electron acceptor due to a high… electron activity.
• Oxygen is involved in the oxidation of carbohydrates, which releases stored energy, carbon dioxide and water

329

What are two sources of molecular oxygen in the atmosphere?

(1) One is the photodissociation of water vapor in which most of the hydrogen escapes into outer space
(2) The other is photosynthesis, in which the hydrogen is used to reduce carbon dioxide into…sugars.

330

What happens to molecular oxygen in the presence of high-energy ultraviolet radiation?

• In the presence of high energy ultraviolet radiation, most of this oxygen is converted into…ozone (O3)

331

List the compounds that contribute to the destruction of the Earth’s ozone layer.

• Chlorofluorocarbons
• methane (CH4) from both anthropogenic and natural sources
• nitrous oxide emitted during agricultural and industrial activities, as well as during combustion of fossil fuels and solid waste
• chlorine monoxide derived from CFCs in aerosol spray propellants

332

What is the role of chlorine monoxide in the destruction of the Earth’s ozone layer and where does it come from?

• derived from CFCs in aerosol spray propellants
• refrigerants, the making of plastic foams, solvents and other sources
• Because the chlorine is involved in the catalytic destruction of ozone, each chlorine molecule has the potential to destroy 100,000 molecules of ozone!

333

What is the Montreal Protocol and what was its goal?

• Montreal Protocol signed by more than 150 countries 1989 to eliminate CFC production by the year 2000, the amount of stratospheric chlorine monoxides will continue to increase

334

What are some potential problems associated with a thinning of the Earth’s ozone layer.

harmful ultra violet radiation, cancers suppress immune system, damages DNA,

335

Distinguish between bioaccumulation and biomagnification and how do these processes occur?

• biomagnification, that is, becoming more concentrated in the bodies of organisms occupying higher trophic levels!
o Get it through eating other organisms containing the toxic chemical.
• Bioaccumulation refers to the increase in concentration of a substance in certain tissues of the bodies of organisms due to absorption from food and the environment over long…periods of time.
• Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost

336

What are the sources of anthropogenic lead in the environment and what happens to such lead?

• The mining, smelting and refining of lead as well as the burning of coal, refuse, sewage sludge and lead-painted surfaces add additional quantities to the atmosphere
• Because lead is emitted into the air in very small particles (less than 0.5 μm in diameter), it gets distributed to all parts of the…earth.

337

What property of the lead entering the atmosphere ensures that it gets widely distributed?

• Because lead is emitted into the air in very small particles (less than 0.5 μm in diameter), it gets distributed to all parts of the…earth.

338

What happens to this atmospheric lead?

• Such lead particles settle on the surface of soil and on vegetation
• Forest canopies are particularly efficient at collecting lead from the atmosphere
• Once in the soil and on plants, lead enters the food chain and is taken up by herbivores that pass it to higher…trophic levels.

339

What effects does the intake of lead cause in humans?

• Intake of lead can cause partial paralysis, mental retardation, loss of hearing and even death!

340

What are the main sources of anthropogenic cadmium in the environment?

• Cadmium is widely used in many industrial processes including the manufacture of nickel-cadmium batteries
• It is also a contaminant of many phosphate fertilizers

341

How do people acquire cadmium and what are some of its effects on the human body?

• In higher doses, it causes excruciating pain in the joints and slowly weakens bones to the point that even coughing can…break bones.
• But the threat to most people is exposure to low levels of cadmium obtained from air, water and diet over long periods of time
• Eating drinking breathing.
• Smoking tobacco.
• The second most important source of cadmium is from leafy vegetables – contaminant of fertilizers.
• Over long-term exposure, cadmium gradually accumulates in the body (primarily in the liver and kidneys), contributing to high blood pressure and…vascular disease.

342

What are some of the uses of mercury in industry?

• It is used in dental fillings, floor waxes, furniture polishes, antibacterial agents, medicines, fungicides and silent switches

343

What are some of the anthropogenic sources of mercury in the environment?

• It also finds its way into the air from the burning of coal and into aquatic ecosystems by deliberate and accidental discharges

344

List two natural sources of mercury in the environment.

• Due to vaporization from the Earth's crust and from vast amounts naturally stored in bottom sediments in the…ocean.

345

What is the major environmental threat from mercury?

• The major threat from mercury is an extremely toxic organic form of mercury called… methyl mercury.

346

What are some of the effects of methyl mercury ingestion on humans?

• Methyl mercury (which stays in the body more than 10 times longer than metallic mercury) can attack the central nervous system, kidneys liver and brain tissue and can cause birth defects

347

How might a lowering of the pH of aquatic ecosystems increase the concentration of methyl mercury in such ecosystems?

• anerobic bacteria in lake sediments could convert relatively harmless elemental mercury and inorganic mercury salts into highly toxic methyl mercury
• These bacteria appear to require a lower pH than is present in most waters

348

What is Minamata disease and what causes it?

• Minimata disease is a neurological syndrome caused by severe…methyl mercury poisoning.
• Symptoms include numbness in the hands and feet, muscle weakness, and damage to hearing and speech

349

What are two chlorinated hydrocarbons that have caused serious environmental problems?

• DDT
• PCBs

350

What characteristics of chlorinated hydrocarbons enable them to enter global circulation?

• Because they are highly soluble in lipids but not in water, they tend to accumulate in the lipids of plants and animals
• They are persistent and stable with a half-life of approximately 20 years
• They are also easily vaporized and much of what gets applied by aerial spraying never reaches the…ground.

351

Why are chlorinated hydrocarbons good candidates for biomagnification?

• Because they are persistent compounds, they tend to become concentrated (biomagnified) in the tissues of animals occupying higher trophic levels

352

What effect to does the ingestion of chlorinated hydrocarbons have on birds?

• In birds, these compounds inhibit the enzyme necessary for the deposition of calcium carbonate in the eggshell, resulting in eggs so thin that they cannot… be incubated.

353

How do chlorinated hydrocarbons affect calcium metabolism and the enzyme ATPase?

• reduced transport of calcium ions across cell membranes

354

Why has the threat from chlorinated hydrocarbons remained in spite of bans on their use in the United States and Western Europe?

• This is because of their widespread use around the world, especially Central and South America and Asia
• Not only native fauna are affected but migratory birds from the Northern Hemisphere come into contact with these compounds on their wintering grounds
• And quantities of pesticides are sent back north to the US, Canada and Europe on fruits and vegetables grown for the…winter market.

355

What are some of the effects of ionizing radiation on humans?

• Such material can cause cancer, genetic defects as well as…kill outright

356

How do radioactive products get released into the atmosphere and what happens to such products?

Radioactive products get released into the atmosphere by nuclear testing
• And as wastes from nuclear reactors, hospitals and research laboratories
• Later they return to Earth along with rain, dust and other material as nuclear fallout
• Once the isotopes reach the Earth, they enter food chains and become concentrated in the bodies of…living organisms.

357

List two fusion products that readily enter grazing food chains.

• fusion products strontium-90 and cesium-137

358

What environmental disaster occurred in Chernobyl, Russia?

• Arctic lichens, which readily take up radioactive particles and gasses drifting onto them, absorbed these elements, passing them onto reindeer, making both meat and milk unsuitable for…human consumption.

359

What were the environmental effects of the Chernobyl disaster on Scandinavian reindeer populations and why?

• Arctic lichens, which readily take up radioactive particles and gasses drifting onto them, absorbed these elements, passing them onto reindeer, making both meat and milk unsuitable for…human consumption.

360

What environmental disaster occurred to the Fukushima Nuclear Power Plant in Japan and what caused it?

• The Fukushima Nuclear Power Plant in Japan experienced a similar nuclear disaster in 2011 that resulted in a meltdown of three of the plant's six nuclear reactors
• The failure occurred when the plant was hit by a tsunami that had been triggered by the magnitude 9.0 earthquake!