Exam 4 Flashcards
(160 cards)
1
Q
1/2 of species obtain energy from what?
A
consuming other organisms
2
Q
species that gain energy from consuming others is called what? what are the 6 different types?
A
heterotrophs
-detritivory
-herbivory
-predation
-parasitism
-parasitoids
-hyperparasitoids
3
Q
draw consumer-resource interaction square
A
x-axis: probability of death
y-axis: duration of association (intimacy)
top left = parasites and arthropod herbivores
bottom left = grazers and browsers
bottom right = predators and seed predators
top right = parasitoids
4
Q
species interactions may _______ over life _________
A
change
stages
example) initially saguaros benefit from the shade of palo verde (commensalism (+/0)). over time they eventually compete for nutrients and water (competition (-/-))
5
Q
what is predation?
A
predator consumes and kills prey, removes prey from the population entirely
(herbivores can be predators)
6
Q
provide an example of the effects of predation
A
on the Caribbean islands, researchers tested if lizard predation was the cause of low spider densities. they introduced 20 individuals of an orb-weaving spider onto five islands with lizards and 5 islands without lizards. over 5 years, the spider densities on the islands without lizards became 10x more abundant than on islands with lizards
7
Q
what is the difference between mesopredators and top predators?
A
mesopredators are lower class, medium sized predators (like hyenas and foxes)
top predators are the large, apex predators (like lions)
8
Q
herbivores can have __________ effects on the species they consume. provide an example
A
substantial
ex) Klamath weed, which is native to Europe and toxic to livestock, was introduced to California in the early 1900s. In the 1950s, biologists introduced a leaf-eating beetle that consumed the weed. Biologists estimate that the beetle has now eliminated 99% of the Klamath weed population in North America (rare-success story)
9
Q
herbivores can be ___________, meaning that they do not kill host directly, but __________ part of the prey (host). over time this increases hosts probability of death and decreases _________. (depends on the duration of association)
A
parasites
consumes
fitness
10
Q
what are parasitoids? ____% of described insect species are parasitoids.
A
unique predators that kill their host but only after the parasitoid’s full development. 10%
they consume the egg/larvae/pupae of other insects
11
Q
parasitoids can manipulate host ___________. what is an example of this?
A
behavior
Cordyceps (genus of fungi) manipulates insect (ants is an example) host behavior to increase their own reproductive fitness.
12
Q
_______ parasitism is actually parasitoid behavior. what is an example of this?
A
brood
cuckoos (and cowbirds) lay eggs in the nests of other bird species and the cuckoo chicks hatch first, then eject or eat the host birds’ eggs. cuckoo chicks mimic the host chicks’ call and are fed and raised by host adults
13
Q
the California ____ _______ insect is a worldwide pest in citrus orchards. a small ___________ ______ lays eggs inside the scale insects, which ultimately ____ them. a simulated outbreak of scale insects on certain trees increased _____________ _______ dramatically and the population of scale insects declined rapidly and remains low.
A
red scale
parasitoid wasp
kills
parasitoid wasp
14
Q
snowshoe hares and Canada lynx populations cycle ___-___ years with lynx cycles lagging about ___ years behind hare cycles (predator-prey cycles)
A
9-10 years
2 years
15
Q
what does top-down control (predation) mean?
A
the abundance of a population is limited by its predators. applies to predator-prey and herbivore-plant interactions.
16
Q
what does bottom-up control (competition) mean?
A
the abundance of a population is limited by nutrient supply or by the availability of food (consumer-resource interactions)
17
Q
what did Carl Huffaker do to experiment predator-prey cycles in lab?
A
(1958) He conducted experiments using western predatory mites as predators and six-spotted mites as prey to understand the conditions that cause predator and prey populations to fluctuate.
results: without predators, prey populations reached high numbers. with predators, predator populations consumed the prey and both populations went extinct. extinction of both populations took longer if oranges were separated far apart; it took longer for predators to find prey. he found that metapopulations and complex environments that allow prey to hide (predators cannot easily find prey) can create stable predator-prey cycles
18
Q
how do prey avoid population extinction?
A
-some prey must be able to disperse/escape/hide
-reproductive capacity of predators must lag prey
19
Q
how do predators avoid population extinction?
A
-disperse (lowers intraspecific competition)
-switch food sources when primary prey are not available
20
Q
what does the rate of change of a population equal?
Lotka-Volterra is a ____________-_______ model based on differential equations (calculates the rate of change in predator and prey populations as each is influenced by one another)
A
the rate of change of population = [population growth rate] - [population decline rate]
continuous-time model
21
Q
what does the rate of change of a prey population as a function of time equal?
A
dN/dt = rN - cNP
P = number of predators
c = probability of an encounter between a predator and prey leading to a prey’s capture
r = intrinsic population growth rate
N = number of prey
22
Q
what does the rate of change of a predator population as a function of time equal?
A
dN/dt = acNP - mP
a = the efficiency of a predator converting consumed prey into predator offspring
m = per capita mortality rate of predators
N = number of prey
P = number of predators
c = probability of an encounter between a predator and prey leading to a prey’s capture
23
Q
a prey population is stable when the rate of change is _____, which means that the addition of prey is balanced by the consumption of prey
A
zero (dN/dt = 0)
24
Q
if rN = cNP, then what does P equal?
A
P = r/c
25
when does prey population increase? when does prey population decrease?
increases when prey additions exceed the consumption of prey (Pr/c)
26
when is a predator population stable?
dP/dt = 0
27
when does predator population increase? when does predator population decrease?
increases when the addition of predators exceeds the mortality (N > m/ac)
decreases when the mortality of predators exceeds the addition of predators (N < m/ac)
28
what is equilibrium (zero growth) isocline?
the population size of one species that causes the population of another species to be stable. for prey, this occurs when P = r/c and for predators when N = m/ac.
29
as the number of predators or prey changes and moves away from the equilibrium isoclines, populations will ___________ __ __________
increases or decreases
30
what is joint population trajectory?
the simultaneous trajectory of predator and prey populations
31
what is joint equilibrium point?
the point at which the equilibrium isoclines for predator and prey populations cross. if either of the populations stray from the equilibrium point, they will oscillate around the point
32
why does an increase in the growth rate of prey (r) lead to an increase in predator population (P) but not they prey population (N)?
increasing the intrinsic growth rate of the prey from r to r' increases the equilibrium number of predators, but not prey
33
the Lotka-Volterra is a very simplistic model, what are 4 assumptions of this model?
-prey population find ample food sources at all times
-the food supply of the predator population depends entirely on the single prey population (not multiple food sources)
-the rate of change of population is proportional to its size
-during the process the environment does not change in favor of one species and genetic adaption is sufficiently slow (essentially no evolution)
34
what is a functional response?
the relationship between the density of prey and an individual predator's rate of food consumption
35
what are the 3 types of functional response curves?
type I: predator rate of prey consumption increases linearly with prey density until satiation
type II: predator rate of prey consumption begins to slow as prey density increases and then plateaus; predators spend more time handling more prey
type III: low predator rate of prey consumption at low prey density, and type II response at high density for three reasons: 1. prey can hide 2. poor search image 3. prey switching
36
what type of functional response curve is the most common and accurate?
Type III
37
what is a lab example of a type III functional response?
researchers manipulated the abundance of isopod and mayfly prey for backswimmer predators. when mayflies were rare, backswimmers consumed fewer mayflies than expected based on their proportion, which indicates prey switching. when mayflies were more common, backswimmers consumed more mayflies than expected, likely because the predators had practice consuming their prey.
38
what are the 4 different methods to avoid getting eaten?
-behavioral
-crypsis
-structural
-aposematism/chemical
39
what are different methods of behavioral defenses?
-alarm calling warns relatives that predators are approaching
-spatial avoidance occurs when a prey moves away from a predator
-some prey reduce activity to avoid being detected by a predator: risk sensitive foraging
40
what is crypsis?
camouflage that either allows an individual to match its environment or breaks up the outline of an individual to blend in better with their background
41
structural defenses reduce a predators' ability to ___________, __________, or __________ prey
capture, attack or handle prey
42
some prey has defenses that are _____________ __________; when the crucian carp detects a predatory fish, it grows muscle mass that allows it to swim faster
phenotypically plastic
43
what is an example of chemical defenses?
when agitated, the Bombadier beetle mixes two chemicals from separate glands to create a boiling hot liquid that is sprays to either kill or injure predators
44
chemical defenses are more effective at deterring predators if the prey can _________ the defense _________ an attack occurs
convey
before
45
what is Aposematism?
warming coloration: a strategy where distastefulness evolves in association with very conspicuous colors and patterns (Monarch butterflies, bright-colored toxic dart frogs)
46
what is mimicry?
when individuals make themselves appear to look poisonous even if they aren't
47
what are the two different types of mimicry?
1. Mullerian mimicry
2. Batesian mimicry
48
what is Mullerian mimicry?
several unpalatable species evolve a similar pattern of warning coloration; similarity in warning confers protection
49
what is Batesian mimicry?
when palatable species evolve warning coloration/patterns that resembles unpalatable species (hover flies and hornet clearwings resemble the common wasp)
50
Batesian mimicry works at a certain extent as long as the population densities of the _________ species are lower than that of the ________ species
mimic species
toxic species
51
defense costs can reduce ________, ___________ and ___________
growth, development, and reproduction
52
what is coevolution?
when two or more species affect each other's evolution; selection for prey defenses should favor the selection for counter-adaptation in predators: " an evolutionary arms race"
53
explain an example of coevolution in nature
the cane toad, which has skin toxins that causes their predators to become sick, or die, was introduced into Australia in 1935. Their predators (black snakes) had no experience with these toxins and many attempted to consume the toads and died. black snake populations evolved resistance to the toxins after getting sick and still surviving and snakes with longer exposure to toads have more resistance. (resistance in measured by reduction in snake swimming speed)
54
what are defenses against herbivory?
many plants produce chemicals at the cost of reduced fitness
55
what is an example of plant using defenses against herbivory
tobacco plants respond to herbivores by producing chemicals including nicotine. researchers compared two tobacco plants, one was the control, and the other was treated with a hormone that blocked nicotine production. the group without hormones produced more nicotine and fewer seeds versus the group with hormones produced less nicotine but more seeds. this shows us that there is a direct energetic cost of producing chemical defenses that takes away from energy spent towards reproduction
56
what tradeoff did Dr. Berenbaum discover?
less toxic plant chemicals are found more frequently versus highly toxic plant chemicals are found less frequently
57
herbivores can cause ___________ defenses in plants
induced (many plant stressors cause induced defenses)
58
provide an example of how herbivores can create induced plant defenses?
when a Brassica plant species is consumed by an herbivore, gene transcription occurs which causes the plant to produce volatile organic compounds (VOCs) which float around in the air and are detected and attracted by different parasitoids that come in and infect the herbivore that is eating the plant.
59
what is a parasite?
does not kill host directly, consumes part of the prey. Increases host probability of death, lowers fitness. Complex life cycles, generally involving 2 hosts. ex: bot fly obligate parasite of mammals.
60
what is an ectoparasite?
parasite that lives on the outside of an organism
61
what are advantages of being an ectoparasite?
-low exposure to host's immune system
-not very difficult to move to and from hosts (including parasite offspring)
62
what type of organisms are ectoparasites?
mostly arthropods (ticks, mites, lice, fleas)
63
what are types of ectoparasites?
-mostly arthropods (ticks, mites, fleas, lice)
-some leeches and lampreys
-nematodes
~4,000 plants (mistletoe)
64
what is an endoparasite?
parasite that lives on the inside of organisms
65
___________ means they live inside the cells of a host versus ___________ means they live between cells of a host
intracellular
intercellular
66
what are advantages of being an endoparasite?
-low exposure to natural enemies
-low exposure to external environment
-high ease of feeding on host
67
what are types of endoparasites?
viruses, helminths, prions, protozoans, bacteria, and fungi
68
what is an example of a prominent ectoparasite?
Chytridiomycosis (Bd): an aquatic fungus (ancient lineage) that lives in the outer layer of amphibian skin and causes ion imbalances. it has always been in ecosystems and rapidly spread through Central America and is now the suspected cause of dozens of amphibian extinctions. more than 1,300 species are susceptible (71 out of 113 Atelopus species extinct).
69
there is evidence for emergence as a novel pathogen (Chytridiomycosis) due to ________ and _____________ factors (low haplotype divergence across continents)
stress and climate
70
what general factors are driving amphibian losses?
-climate change
-contaminants
-disease
-competition
-collecting amphibians
-invasive species
-predation
-habitat destruction
-UV B radiation
71
what are scientists currently doing to combat chytridiomycosis?
operation "purple rain": spray amphibian individuals with a bacteria mixture that decreases parasitic infection spread
72
describe an example of a multi-trophic interactions
in Hawaii, malaria (vector = mosquitoes) is infecting bird populations (I'iwi is an example) and feral pigs that feed on native tree ferns create little divots in the trees that create small water puddles that allow mosquitos to breed easier. spread of malaria depends on several factors:
-warming temperatures expanding disease range
-feral pigs expanding disease range
-invasive bird competition
-malaria susceptibility
73
parasite and host dynamics are similar to predator-prey dynamics, but parasites often have a higher ____________ _____ than their hosts and do not often ______ their hosts
reproductive rate
kill
74
provide an example of parasite-host cycle that occurs over 2 years
year 1: female ticks lay eggs in the spring, tick eggs hatch into tick larvae, larval ticks attach to an infected rodent in the summer, feed on the rodent's blood, acquire the bacterial infection and then fall off. during years of plentiful acorns, rodent populations increase and provide more hosts for bacteria and hosts. infected larval ticks molt into tick nymphs which survive winter under leaves.
year 2: infected nymphs attach to various animals in the spring, feed on a host's blood and then fall off. tick nymphs molt into adult ticks which then attach to a dear in the fall, feed on its blood, mate with other ticks and then fall off.
75
_____________ ______________ is when a parasite is transmitted from a parent to its offspring
vertical transmission
76
_____________ ________________ is when a parasite moves between individuals other than parents and offspring (uses a vector like mosquitos)
horizontal transmission
77
what 4 factors influence the probability of infection?
-mode of entering the host: piercing tissue (leeches) or reliance on a vector (malaria)
-ability of parasite to jump between species: a lethal parasite that specializes on one host may face extinction; solution is to infect multiple species (blue flu, HIV)
-reservoir species: species that carry a parasite but do not succumb to disease. they can be a continuous source of parasites as other hosts become rare
-counterattacks to host's immune system: avoiding detection by incorporating into chromosomes (HIV). or form protective outer layer (schistosomes)
78
Lyme disease prevalence is much higher the year following ______ _______________
oak masting
79
red oaks ______ every 2-5 years. ______ populations fluctuate with masting events, and high acorn densities also attract __________ which are __________ to adult deer ticks. adult ticks drop and lay eggs in soil, which then the eggs hatch into larvae which attach to _________, which are the main __________ hosts to Lyme disease.
mast
mice
deer
hosts
mice
reservoir
80
____% more ticks become infected with Lyme disease during __________ years
40%
masting
81
_________ _________ outbreak occurs every 10 years. their larvae emerge with oak leaves and can __________ entire forests. _______ are important predators of ___________ _________ _________
Gypsum moths
defoliate
gypsum moth pupae
82
what is infection resistance?
ability of host to prevent infection from occurring (through immune response or behavior)
83
what is infection tolerance?
ability of host to minimize harm from infection
84
_______________ can control infection resistance and can influence tolerance
vaccinations
85
what is the susceptible-infected-resistance (SIR) model?
the simplest model of infectious disease transmission that incorporates immunity.
86
what variables do you need to know for the SIR model?
S = number of individuals susceptible to a pathogen
I = number of individuals that become infected
R = number of individuals that develop resistance
b = rate of transmission (via contact) between individuals
g = rate of recovery and development of immunity
87
what does the ratio of new infections to recoveries is the reproductive ratio (Ro)?
Ro = S x I x b / I x g (rate of infection / rate of recovery)
88
when will the infection spread?
Ro > 1
89
when will the infection fail to spread?
Ro < 1
90
how can people reduce Ro?
create vaccines that reduce susceptibility (rate of infection)
91
hosts develop a range of responses (___________) to combat parasites
defenses (ex: apes will eat specific plants if they feel sick)
92
____________ helps the immune system rapidly evolve
recombination: the reshuffling of genes that can occur as DNA is copied during meiosis and chromosomes exchange genetic material
93
how does genetic recombination relate to the red queen hypothesis?
genetic recombination (sexual reproduction) allows host to evolve at a rate that counters the rapid evolution of parasites. hosts and parasites are constantly engaged in an evolutionary arms race (evolving defenses (host) and overcoming defenses (parasites)) just to maintain fitness.
94
this evolutionary "arms race" results in a _________ __________ ________ where neither hosts nor parasites __________ gain the upper hand.
dynamic steady state
permanently
95
what is competition?
use or defense of a resource by one individual that reduces the availability to another individual of the same species (intraspecies) or other species (interspecific)
96
what is a resource?
any substance or factor that is consumed or used by an organism and that supports increased population growth as its availability increases
97
what is Liebig's law of the minimum?
a population increases until the supply of the most limiting resource prevents it from increasing further (not all resources limit consumer populations)
98
provide an example of Liebig's law of the minimum
silica is a limiting resource for diatoms, such as Asterionella formosa and Synedra ulna. the two species have different demands of this limiting resource. these two species have two different carrying capacities (1micromole versus 0.4 micromole) and the abundance of silica in the environment is not sufficient to support the population of Asterionella (which has a higher carrying capacity) but it can support Synedra because they can persist at lower silica concentrations than Asterionella. When grown together, Synedra persists and Asterionella declines to extinction.
99
what are complete competitors?
two species that cannot coexist indefinitely on the same resource because one species is often a better competitor and survives better when resources are scarce. (competitive exclusion principle)
100
how did Tansley first test the competition of plants (Galium)?
(1917) Tansley observed that closely related species grow in different habitats, and he predicted that 1. grown alone, each species will grow best in its native soil type. 2. when both species are grown together, the outcome of competition will depend on the soil type.
101
what did Darwin suggest experimenting on common garden competition?
Darwin suggested that competition is most intense between related species because they have similar traits and consume similar resources, therefore natural selection should favor differences in habitat use for related species that strongly compete
102
what was the common garden experiment?
scientists grew two similar species of plants, Heath bedstraw and White bedstraw, alone and then together in one area. the health bedstraw grows best in acidic soils versus the white bedstraw grows best in alkaline soils. so when they were planted together the white bedstraw outcompetes the health bedstraw in alkaline soils and the health bedstraw outcompetes the white bedstraw in acidic soils.
103
___________ experiments are one method to measure animal competition
exclosure
104
provide an example of an exclosure experiment
hypothesis: large granivore rodents are superior competitors and limit abundance of small rodents.
prediction: removing large granivores will result in population increase in small granivores
experiment: mesh enclosures prevent large granivores from entering plots, but small granivores are not excluded. compare this with control plots that allow all animals to enter
results: numbers of small granivore rodents increased on the removal plots relative to the control plots.
105
how do we include a second species to the logistic growth model?
add
1. the number of individuals of the second species (N1 or N2)
2. how much each individual of the second species affects the carrying capacity of the first species (competition coefficient)
106
what is the competition coefficient?
variables that convert between the number of individuals of one species and the number of individuals of another species
ex: the food needed to support 100 rabbits (species 1) would also support 200 squirrels (species 2)
107
what is the formula for logistic growth model including a second species?
dN1/dt = r1N1 (1 - [N1 + αN2] / K1)
dN2/dt = r2N2 (1 - [N2 + βN1] / K2)
α = competition coefficient for species 1 (converts individuals of species 2 into the equivalent number of species 2)
β = competition coefficient for species 2
108
two species may be able to coexist when each is better at persisting at low levels of ______________ _______________
different resources
109
provide an example of two species that can coexist using different resources
Cyclotella diatoms use silicon more efficiently than Astrionella diatoms, so they can persist at low levels of silicon. Astrionella use phosphorus more efficiently, so they can persist at low levels of phosphorus. When grown together at low (0.6) or high (455) ratios of Si/P, Cyclotella and Astrionella dominated, respectively. When grown together at an intermediate (38) ratio of Si/P, both species coexisted because each was limited by a different resource.
110
coexistence of two species is most likely when __________ ___________ competition is weaker than __________ ____________ competition
inter-specific
intra-specific
111
__________ barnacles live in the upper intertidal zone and are desiccation tolerant. ___________ barnacles live in the lower intertidal zone and are not desiccation tolerant. ___________ barnacles can grow quickly and pry off the ____________ from rocks (meaning they are better competitors)
stellate
rock
rock
stellates
112
stellates are excluded by ________ ___________, meaning that when rock barnacles are removed, stellates quickly move into their space.
rock barnacles are excluded by ________ ___________, meaning that when stellates are removed, rock barnacles cannot utilize the space.
biotic competition
abiotic competition
113
therefore, the stellate barnacles have a _________ ____________ niche because they can survive in both the upper and lower intertidal zones.
the rock barnacles have a _________ ____________ niche because they can only survive in the lower intertidal zone.
greater fundamental (all the abiotic conditions in which an organism can survive)
smaller fundamental
114
both rock and stellate barnacles have a relatively equal __________ ____________ because competition between the two restricts where they can each actually inhabit
realized niche (where an organism is actually found; restricted due to (biotic) species interactions
115
there are __________ between competitive ability and resistance to predators or herbivores; the ________ competitive organisms are often the most susceptible to predation or herbivory
tradeoffs
most
116
provide an example of how predators can reverse the outcome of competition
spadefoot and southern toads are more active and forage more than spring peepers. When placed in a pond without predatory newts, the spadefoot and southern toads outcompeted the peepers. When placed in a pond with newts, the high activity of the toads allowed the predators to more easily find them, allowing the less active peepers to dominate.
117
provide an example of how herbivores can alter the outcome of competition
in fallow fields of the northeastern US, goldenrod can grow more than a meter high and cast shade on shorter competitors. every 5-15 years, a species of beetle that specializes on goldenrod achieves very high densities. to determine the effect of this outbreak, researchers sprayed some fields with insecticide that killed the beetles and left other fields unsprayed. In sprayed plots, goldenrod continued to dominate; in unsprayed plots, competitors became much more abundant.
118
what is exploitative competition?
competition in which individuals consume and drive down the abundance of a resource to a point that other individuals cannot persist
119
exploitative competition is considered _________ competition because it occurs through a shared resource
indirect
120
what is interference competition?
when competitors do not immediately consume resources but defend them; considered direct competition
121
what is apparent competition?
when two species have a negative effect on each other through an enemy-including a predator, parasite, or herbivore.
122
what is an example of interference competition
top predator vs. mesopredators
mesopredators vs. scavengers
123
what is allelopathy?
a type of interference competition that occurs when organisms use chemicals (allelochemicals) to harm their competitors
124
allelopathy can be an effective strategy for __________ plants
invasive
125
provide an example of allelopathy
The common reed is found in wetlands throughout the world; in North America, some genetic strains are native, and others are invasive. Roots of the reed produce gallic acid, which is highly toxic to other plants. Chemicals produced by invasive strains were much more lethal than those produced by native strains, which allows the invasive strain to spread.
126
what is a mutualistic relationship?
a positive interaction between two species in which one species receives benefits that only the other species can provide. mutualisms are common and can affect populations, species, communities, and ecosystems
127
what are generalists?
a species that interacts with many other species
128
what are specialists?
a species that interacts with one other species or a few closely related species
129
what are obligate mutualists?
two species that provide fitness benefits to each other and require each other to persist
130
what are facultative mutualists?
two species that provide fitness benefits to each other, but the interaction is not critical to the persistence of either species
131
what is an example of obligate mutualism?
leaf cutter ants: food for ants, food and protection for fungi. each ant species (47 species) cultivates a different strain of fungus. they've been practicing fungiculture for 50 million years. a mature colony has 8 million individuals, and they harvest >17% of total leaf production in tropical rainforests
132
most of mutualistic relationships occur at the ___________ _________
microscopic level (bacteria, protists)
133
what are prokaryotes?
first organisms; single-celled bacteria and archaea without distinct organelles
134
what are eukaryotes?
organisms with distinct cell organelles that evolved from prokaryotes
135
what are major functional groups of bacteria/archaea?
1. chemoheterotrophs
2. photoautotrophs
3. chemoautotrophs
136
what are chemoheterotrophs?
-carbon and energy source are organic compounds. different types:
1. saprophyte: feed on dead plant or animal materials or humic substances
2. predator: feeds on living prey
3. symbiont: organic compounds from host, beneficial/ neutral
4. pathogen: organic compounds from host, detrimental
137
what are photoautotrophs?
-energy from light
-carbon source from CO2
138
what are chemoautotrophs?
energy from inorganic compounds
-carbon source: CO2
-ammonia oxidizing bacteria in soils
-iron oxidizing bacteria in lava beds
139
what are biocrusts?
assemblage of different microbes, bacteria, archaea that form a very thin layer at the very beginning of soil formation practices. they are very important in drylands and degraded environments
140
what factors affect biocrusts?
-local climates
-land-use history
-subsurface soil microbial community structure
141
what affects do biocrusts have on the soil?
-surface albedo
-soil hydrology
-soil stability
-nitrogen cycling
-carbon cycling
142
plant-fungal associations arose __________
more than 460 million years ago
143
mycorrhizae: myco: ________ and rrhizae: _______
fungus
root
144
what are the different types of mycorrhizae?
endomycorrhizal (AM): 100's of species (>90% land species)
ectomycorrhizal (ECM): 1000's of species, douglas-fir, mushrooms, puffballs, truffles (Ascomycota and Basidiomycota). (only a few plant species)
145
what're the benefits of mycorrhizae to plants?
-increase nutrient uptake by providing greater root surface area (P, N, Ca, K and amino acids)
-increase root longevity
-increase soil aggregate stability
-protection against pathogen infection and root predation
146
what're the benefits of mycorrhizae to fungi?
-photosynthate (sugars) from plants provides carbon to fungus
-plant roots minimize environmental fluctuations and stress -- gives some protection
147
not all ________ harm plants. provide an example of this
insects
ex: acadia (tree) provide domatia (home) and Beltian bodies, extrafloral nectaries (food) to ants. ants protect trees against herbivores and plant competitors. removing ants reduced acadia tree survival rate
148
plant ______________ are found inside plant leaves and have great functional diversity
mycobiomes
149
fungal pathogens cause >730,000 tons of ________ loss annually
cacao. fungal biocontrol: Trichoderma (limited success)
150
many plants rely on _________ to carry pollen between flowers. plants have evolved __________ ___________ to entice pollinators to visit their flowers.
animals
reward mechanisms
151
how does the common honeybee transfer pollen?
when the common honeybee consumes nectar and pollen from a flower, pollen becomes attached to its body and as it moves among flowers, it transfers pollen
152
how do flowers that're pollinated by hummingbirds look? what about bats?
flowers pollinated by hummingbirds have long, tubular flowers that are only accessible to hummingbirds which have long beaks. bat-pollinated flowers are large and often only open at night; they contain large amounts of pollen to attract the pollinators.
153
most pollinator, seed dispersers, and predators are an example of ____________ ____________
facultative mutualism
154
what is a specific example of obligate mutualism?
Yucca elata is pollinated only by Tegeticula yuccasella moth; moth only eats these seeds. Female deposits pollen directly on stigma. moth larvae grow in ovule and eat up to 30-40% of ovaries (developing seeds). Yucca aborts flower (killing all moth larvae) if moth lays too many eggs = selection pressure on moth to limit egg load.
155
__________ occurs when one species receives a benefit but does not provide one in return. natural selection should favor _________, but should also favor mechanisms that enable _________ against __________
cheating (x2)
defense against cheating
156
provide an example of how cheating can be avoided?
if mycorrhizae reduce the benefit they provide to the plant, the plant should respond by providing less benefit to the fungus.
Researchers planted onions in pots that divided roots among soil with mutualistic fungi and soil with non-mutualistic fungi. Plants were able to thwart cheating by sending more photosynthetic products to the
beneficial fungi.
157
mutualisms can have effects at the level of ____ _____________
an ecosystem
158
provide an example of how mutualism effects an ecosystem
Researchers investigated how a grassland ecosystem would respond to different numbers of mutualistic fungal species in the soil. Grassland communities with soils containing more fungal species took up a greater amount of phosphorus. More diverse fungal communities also led to greater root and shoot biomass in the ecosystem.
159
loss of dispersers can result in a reduction in __________ ____________
plant abundance
160
provide an example of how a loss of dispersal causes a reduction in plant abundance?
on Mauritius, several species of large dispersing organisms have gone extinct, such as the high-backed tortoise; tree species that require these animals to consume their seeds for dispersal have declined in abundance. researchers brought in non-native tortoises which have a similar capacity to consume seeds, and this activity of the turtles has increased the abundance of declining tree species
