Community Ecology Flashcards
(206 cards)
1
Q
Ecological community
A
1) The small fraction of this enormous global collection of species that can be found at any particular place
Morin p. 3
2
Q
Community ecology
A
1) The study of patterns and processes involving at least two species at a particular location
2) Can include predator-prey interactions and competition, things that are typically considered as part of population ecology
Morin p. 5
3
Q
Population ecology
A
Focuses on patterns and processes involving single-species groups of individuals
Morin p. 5
4
Q
Guild
A
Collection of species that use similar resources in similar ways Morin p. 6
5
Q
Taxocene
A
Set of taxonomically related species within a community (e.g. birds, lizards, fish)
Morin p. 6
6
Q
Functional group
A
A collection of species that are all engaged in some similar ecological process (often defined in arbitrary ways), e.g. primary producers
Morin p. 6
7
Q
Trophic levels
A
Provides a way to recognize subsets of species within communities that acquire energy in similar ways (e.g. primary producers, herbivores, primary carnivores)
Morin p. 6
8
Q
Food chains and food webs
A
Describe patterns of material and energy flow in communities, usually by diagramming the feeding links between consumer and the species that they consume
Morin p. 6
9
Q
Ecosystems
A
Consist of one or more communities, together with abiotic surroundings
Morin p. 7
10
Q
Ecosystem engineers
A
Species that physically alter the environment through their presence or behavior (e.g. beavers)
Morin p. 7
11
Q
Four ways to delineate communities
A
1) Physically, by discrete habitat boundaries
2) Taxonomically, by the identity of a dominant indicator species
3) Interactively, by the existence of strong interactions among species
4) Statistically, by patterns of association among species
Morin p. 7
12
Q
Physically-defined communities
A
Include assemblages of species found in a particular place or habitat (e.g. lakes, ponds, rotting fruits, whale falls OR forests into savannas into grasslands)
Morin p. 7
13
Q
Biomes
A
1) Basic categories of communities that differ in their physical environments and in the life styles of their dominant organisms
2) 36 biomes
3) Global distribution of biomes is heavily influenced by precipitation and temperature
(Whittaker 1975)
Morin p. 7,9
14
Q
Taxonomically-defined communities
A
Usually recognized by the presence of one or more conspicuous species that either dominate the community through sheer biomass, or otherwise contribute importantly to the physical attributes of the community (e.g. Redwood forests, beech-maple forests)
Morin p. 9
15
Q
Statistically-defined communities
A
1) Consists of sets of species whose abundances are significantly correlated, positively or negatively, over space or time.
2) Species composition then has a geometrical interpretation as a directional vector, or arrow
Morin p. 9
16
Q
Environmental gradient and abundance
A
ENTER FIG 1.3
17
Q
Graphical representation of statistically-defined community
A
ENTER FIG 1.4
18
Q
Interactively-defined community
A
Subsets of species in a particular place or habitat whose interactions significantly influence their abundances. Only some, and perhaps none, of the species in a physically defined community may constitute an interactively defined community.
E.g. Hairston (1981) used this approach to point out that only a small subset of the species of salamanders found in the mountains of North Carolina could be shown to interact and affect each other’s abundance.
Morin p. 14
19
Q
Species richness
A
Total number of species present Ssub-t, May 1975
Synonymous with our most basic notions of biodiversity.
Morin p. 14
20
Q
How to know if estimate of species richness is accurate?
A
1) Plot the cumulative number of species found against the amount of sampling effort. Beyond a certain amount of effort the species versus effort curve should reach an asymptote.
2) This asymptote provides a reasonable estimate of the number of species present.
3) Comparisons among communities that have been sampled with different amounts of effort can be made by using rarefaction curves
Morin p. 15
21
Q
Shannon Index of Diversity
A
S= total number of species present
psubi = fraction of individuals in the sample that belong to species i
H prime = sum of all species (-psubi*ln(psubi))
Accounts for both number of species and distribution of species
Morin p. 15
22
Q
Species evenness
A
J=Hprime/Hmax, or shannon diversity index over value of shannon diversity that would be obtained with an equal distribution
Morin p. 15
23
Q
Simpson index of dominance or concentration
A
1) Expressed as the reciprocal of Simpson’s index, lambda
2) lambda = sum of all species (psubi^2) where psubi is the fraction of individuals in the sample that belong to species i
3) This is effectively the probability that any two individuals drawn at random from a sample will belong to the same species
4) So a high lambda (high probability of re-sampling the same individual) means a low Simpson index (1/lambda) means low diversity.
Morin p. 16
24
Q
Alpha diversity
A
Local diversity within a single type of habitat (Whittaker 1975)
Morin p. 16
25
Beta diversity
Within a large geographic region, the turnover or change in species composition among different habitats (contributes to additional diversity)
Morin p. 16
26
Gamma diversity
Gamma diversity is related to alpha and beta diversity in that it equals the average alpha diversity among habitats plus the beta diversity within the region
Dsubg=avg(Dsuba) + Dsubb
Useful in determining if local diversity is determined largely by regional diversity or by local processes
Morin p. 16
27
Importance value of a species
1) Usually a measure of the fraction of total number of individuals or biomass in the sample accounted for each species plotted against the importance rank
2) Three common types are the broken-stick distribution, geometric series, and lognormal distribution
ENTER FIG 1.6
Morin p. 17
28
Predation and energy flow
(-/+), drives processes of energy and material flow up through food webs
Morin p. 19
29
Competition
(-/-) mutually negative
| Morin p. 19
30
Amensalism
(0/-), one sided competitive interaction, where one species has a negative effect on another but the other has no detectable influence on the first
E.g. shading out one plant by another or allelopathy (inhibiting growth of one plant from the secretions of another)
Morin p. 19
31
Mutualism
(+/+), mutually positive interaction between a pair of species, where each has a positive effect on the other
E.g. oxpecker and zebra (food and pest control)
Morin p. 19
32
Commensalism
(0/+), one-sided mutualistic interaction, where one species has a positive effect on another species, but the second species has no net effect on the first
E.g. Remoras on sharks
Morin p. 19
33
Interspecific competition
(-/-), mutually negative interaction between two or more species within the same guild or trophic level. Can manifest in reduced abundance, decreased fitness, or a decrease in some fitness component such as body size, growth rate, fecundity, or survivorship.
Morin p. 24
34
How to study interspecific competition
Observational
1) Searching for negative correlations between the abundances of ecologically similar species
2) Using interspecific differences in morphology or resource use to infer possible competitive interactions (as evidence that species must differ by some fixed amount in order to avoid competitive exclusion)
Drawbacks: competition may not be the sole mechanism of these differences
Experimental
1) Manipulations of competitors in a lab or in a natural setting
Drawbacks: not always feasible or ethical, may not include other important ecosystem dynamics
Morin p. 25
35
Character displacement
Differences in morphology of ecologically similar species are greater in sympatry than in allopatry
Morin p. 25
36
Exploitation competition
Operates indirectly by the depletion of some shares resource (outdated term)
Morin p. 26
37
Interference competition
Involves direct interactions between species (outdated term)
| Morin p. 26
38
Scramble competition
Usually involves resource utilization (outdated term)
| Morin p. 26
39
Contest competition
Involves a behavioral interaction between species (outdated term)
Morin p. 26
40
Consumption (competition)
Happens when one species inhibits another by consuming a shared resource
E.g. competition between granivorous rodents and ants for seeds
Morin p. 26
41
Pre-emption (competition)
Occurs primarily between sessile organisms, Results when physical resource is occupied by one organism and made unavailable to others
E.g. rocky intertidal barnacles (settlement), encrusting bryozoans and corals.
Morin p. 26
42
Overgrowth (competition)
Does not require direct contact, only requires that growth of one species is inhibited by the growth of another
E.g. trees overshading one another and excluding shade intolerant species, encrusting bryozoans and corals.
Morin p. 26
43
Chemical interactions (allelopathy) (competition)
Chemical warfare between competitors
E.g. allelopathy in plants where one plant releases growth-inhibiting toxin that influences a nearby plant
Morin p. 26
44
Territoriality (competition)
Aggressive behavioral exclusion of organisms from specific units of space that are defended as territories.
E.g. brightly colored coral reef fish
Morin p. 26
45
Encounter competition
Results when non-territorial encounters between foraging individuals result in negative effects on one of both of the interacting individuals
E.g. laboratory studies of parasitoids foraging for prey, when two parasitoids encounter each other they may interact in ways that cause them to stop foraging, or to leave for a site where there may be more prey
Morin p. 27
46
Asymmetric competition
Most competition is asymmetric, with one species exerting control over another. Extreme cases can turn into amensalisms.
Morin p. 27
47
Descriptive models of interspecific competition
Describe how the abundance of one species affects the abundance of another, without specifically including a particular competitive mechanism
E.g. logistic model (adapted as the Lotka Volterra model)
Morin p. 27, 29
48
Mechanistic models of interspecific competition
Explicitly include information about the mechanism responsible for the effects of one species on another
Morin p. 28
49
Local stability (models)
If the population changes slightly will it return to a certain local equilibrium value
Morin p. 28
50
Global stability (models)
A system will return to the equilibrium point from any initial population value
Morin p. 28
51
Zero growth isoclines (models)
Equations for two lines that yield zero population growth for each species
Morin p. 30
52
Four possible competitive situations in Lotka Volterra model
1) unstable equilibrium, where K2>K1/alpha12 and K1>K2/alpha21
2) competitive exclusion of species 1 by species 2, where K2>K1/alpha12 and K1K2/alpha21
4) stable equilibrium where both species coexist K2
53
Priority effect (models)
Where initial conditions determine the outcome of an interaction
Morin p. 32
54
Non-additivity (models)
The existence of higher order interactions, when the pairwise effects of multiple competitive interactions (>2 species) cannot be added as the effect of one species on another depends on the complexity of the system
Morin p. 32
55
Liebig's Law of the minimum
Where species require several resources to grow, growth rate will be determined by the resource in shortest supply
Morin p. 37
56
Neighboorhood models
How individual plants respond to variation in abundance of their immediate neighbors
Morin p. 40
57
Chaotic dynamics
When species abundance varies irregularly over time
| Morin p. 39
58
Niche
1) No two species will be found to occupy the same niche
2) Implies that a competitive relationship between the species is important in affecting the ways in which species make their livings
3) Fundamental niche = where the species can persist
4) Realized niche = potential impact of other species in limiting the range of conditions successfully exploited by a given species
Grinnell (1914)
Morin p. 46
59
Competitive exclusion principle
Complete competitors cannot coexist, Hardin (1960)
| Morin p. 46
60
Diffuse competition
No single species mat account for a large effect, but collectively, the impact of many species may be severe
Morin p. 47
61
Resource utilization niche
Focuses on consumable resources, or factors that serve as surrogates for those resources, such as different microhabitats
Morin p. 47
62
Niche complimentarity
Species that exhibit high overlap in habitat use, tend to have low overlap in food and vice versa
E.g. anolis lizards have a low overlap in structural habitat when there is a high overlap in prey size
Morin p. 49
63
Apparent competition
1) When the presence of multiple non-competing prey species elevates predator abundance above levels maintained by single prey species, which increases predation pressure on multiprey assemblages
2) E.g., Gastropods Tegula and Astraea do not compete with bivalves Chama and Mytilus, but their combined presence increases predator populations
3) E.g., Infestations of Pacific mites are more effectively controlled when Willamette mites are present as this increases predator abundance
Morin p. 51, 190-2
64
Replacement series model design
Used to show whether the per capita effects of interspecific competitors differ from those of intraspecific competitors, useful for frequecy-dependent competition
Morin p. 60
65
Example of interspecific competition in marine communities
1) Connell's experiments on Chthamalus and Balanus
2) Chthamalus absence from Balanus zone coaused by competitive exclusion
Morin p. 63
66
Example of interspecific competition in marine plants
1) Dayton's experiment on alga
2) The dominant alga in the lower intertidal zone had both negative competitive effects and positive effects on other alga species
3) The dominant alga would "shade out" other species and created favorable understory conditions for other species
Morin p. 65
67
Example of interspecific competition in terrestrial communities
1) Hairston's experiments on terrestrial salamanders
2) Found results similar to Connell's barnacle experiment with salamander and elevation
Morin p. 65
68
Asymmetric competition and predicting competitive ability
1) Competitive interactions are often strongly asymmetric
2) Asymmetry possibly due to differences in characteristic sizes of competitors, with larger predators having larger per capita impacts than smaller ones, OR differences in activity levels, which are probably correlated with rates of foraging and resource depletion
Morin p. 81
69
Overlap and interspecific competition
1) Hairston believed that high overlap yields weak competition and vice versa
Morin p. 65
70
Interphyletic competition
Competition amongst animals in different phyla, e.g. granivorous rodents and ants exploit seeds
Morin p. 83
71
Non-additive competition
1) In simple systems, aggregating the competitive effects of pairwise interactions between species is sufficient (additive interactions)
2) In more complex systems, per capita effects of interspecific competitors depend on the identity and density of other species in the system (non-additive or higher order interactions)
Morin p. 83
72
Predation in marine communities
1a) Paine and Pisaster
1b) Pisaster enhanced the number of species that managed to coexist in a limited area because they precent competitive exclusion
1c) Pisaster is a keystone species
2a) Lubchenco and Littorina
2b) Density of Littorina influenced the algae community
2c) For a predator to enhance the prey diversity, it must feed preferentially on the competitively dominant prey species
Morin p. 93-4
73
Predation in terrestrial communities
1) Tansley and Adamson's grazing rabbits
2) Ungrazed plots showed successional changes
3) Herbaceous species naturally present in the grassland were maintained by rabbit grazing, and would be competitively excluded in the absence of grazing
Morin p. 97
74
Intraguild predation example
1) Lizards eat some spiders, but also compete with spiders for insects
2) When lizards are absent, there are a high number of insects, and plants develop insect defenses
2) When lizard are present there are fewer insects and plants do not develop defenses
Morin p. 101
75
Janzen-Connell hypothesis
1) Pathogens typically live close to plants
2) Seeds that disperse farther from the established parent will have a higher probability of survival because they will not be exposed to pathogens
Morin p. 103
76
Size-efficiency hypothesis
1) Brooks and Dodson and Hrbacek
2) Larger zooplankton are more efficient competitors
3) Small zooplankton cannot coexist with competitively superior large plankton
4) Planktivorous fish selectively consume larger zooplankton, releasing small zooplankton
5) Suggests that predators alter the size-structure and species composition of zooplankton assemblages
Morin p. 107
77
Can predators have negative effects on species richness?
1) Yes, for example pitcher plant mosquito larvae
2) Larvae consume protists, but protists do not have many competitors, so there was no release of other prey species when mosquitos were removed
Morin p. 107
78
Inducible defenses
1) Defenses only produced in response to predator cues
2) Daphnia produce spines when predators are present
3) Due to phenotypic plasticity
Morin p. 110
79
Constitutive defenses
1) If the risk of predation is high and constant, prey produce permanent defenses
Morin p. 110
80
Errington's hypothesis
1) Predators often have little actual impact on total prey abundance because they are consuming prey that could not secure safe territories or refuges from predators
2) Assumes that prey populations are ultimately regulated by competition among prey for predator-free sites
Morin p. 111
81
HSS hypothesis
1) Herbivores are surrounded by a surplus of food, so herbivores are not limited by competition
2) Detractors: chemical defenses of plants, plant specialists
3) Objection to detractors: at least one species will be able to eat another species of toxic plant
Morin p. 111-2
82
Fretwell's extension of HSS
1) In even numbered food chains, herbivores are limited by competition
2) In odd numbered food chains, herbivores are limited by predation
Morin p. 113
83
Menge-Sutherland hypothesis
1) Within a community, competition plays an increasingly important role in guild organization (community structure)
2) Between communities, predation plays an increasingly important role in community organization
Morin p. 115
84
Connell's hypothesis of physical stress
1) The effects of predators on community structure were to some extent determined by the rigors of the physical environment, with predation being less important in physically harsh environments, e.g. rocky intertidal
Morin p. 116
85
Trade-off between competition and predation
1) Competitively superior animals likely have a trade-off with predation
2) Characteristics that make a species competitively superior may decrease fitness via predation, e.g. large size makes you more conspicuous
3) The more energy put into competitive defenses detracts from energy allocated to prey defenses
4) Competitive ability increases with rate of resource acquisition and resistance to predation decreases with increasing rate of resource acquisition
Morin p. 116-8
86
Neutral stability
1) Used to describe dynamics of the Lotka-Volterra predator/prey model
2) Consequence of the peculiar lack of density-dependence in this model
3) Means that oscillations continue ad infinitum
4) Including density-dependence shifts behavior from neutral stability to local stability about an equilibrium point (damped oscillations)
Morin p. 122-3
87
Leslie-Gower predator-prey model
1) Incorporates density dependence in both the prey and predator populations
2) Yields local stability
Morin p. 126
88
Holling-Tanner predator-prey model
1) Incorporates a maximum attack rate to predator prey models
2) Yields either a stable equilibrium or stable limit cycle depending upon initial conditions
Morin p. 125
89
What effect does time lag have on predator prey models?
Lags destabilize the system
| Morin p. 127
90
Predation with multiple prey
Predation can lead to stable coexistence of prey where predator attacks two prey similarly, or where the competitively superior prey is consumed at a higher rate
Morin p. 129
91
Eltonian Pyramid
1) Small organisms at the base of the food chain are more numerous than their larger predators
2) It is thermodynamically impossible to have an inverted pyramid of productivity since the rate of energy accumulation at upper trophic levels cannot exceed that in lower levels
Morin p. 139
92
Ecological efficiency
1) Measure fo the fraction of energy entering one trophic level that is passed on to the next higher trophic level
Morin p. 139
93
Source food webs
Describe the feeding relations among species that arise from a single food source
Morin p. 140
94
Sink food webs
Describe the feeding relations that lead to sets of species consumed by a single top predator, e.g. Pisaster sink webs
Morin p. 140
95
Community webs
Describe the entire relations in a particular community, although this ideal goal is almost never realized in practice
Morin p. 140
96
Trophic position
Consists of basal species, intermediate species, and top predators
Morin p. 140
97
Food web links
1) can be directed and undirected
2) directed links represent the net effect of one species on another, demonstrate who eats whom
3) undirected links represent that there is some form of relationship or interaction between species
Morin p. 141
98
Connectance (food webs)
Describes how many possible links in a food web are present (how many individuals are capable of interacting), richness of species interactions
Morin p. 142
99
Linkage density (food webs)
The average number of feeding links per species (is a function of connectance)
Morin p. 142
100
Compartmentation (food webs)
The extend to which a food web contains isolated subwebs that are richly connected within subwebs but which have few connections between subwebs
Morin p. 142
101
Same chain omnivory
Occurs when a species in a food chain feeds on trophic levels in addition to the one immediately below its own trophic level
Morin p. 142
102
Different chain omnivory
Occurs when a species feeds at different levels in multiple food chains
Morin p. 142
103
Life-history omnivory
Occurs when different life-history stages or size classes of an organism feed on two different trophic levels, e.g. herbivorous larvae of frogs transform into insectivorous adult frogs
Morin p. 142
104
Cycles and loops (food webs)
Occur if species have reciprocal feeding relations
105
Rigid circuit (food webs)
Overlapping of predators based on the prey species they exploit
Morin p. 142
106
Intervality (food webs)
Demonstrates the series of overlap between predators, indicates the number of dimensions necessary to determine the niche of a predator (how many trophic dimensions characterize a niche)
Morin p. 143
107
Food web patterns
1) 4:3 ratio of predator to prey (prey as determined by trophospecies)
2) Food webs are typically interval in nature --> cascade model can produce interval webs
3) Three-species loops are infrequent
4) Linkage density is constant across collections of food webs and connectance should decline hyperbolically with increasing species richness
5) Average proportions of links between basal, intermediate, and top species seems relatively constant
6) Food chains are relatively short
7) Omnivory is infrequent
8) Connectance varies between webs in constant and variable environments (increased variability yields decreased connectance)
9) Webs are not strongly compartmented (high interconnectedness
10) Food chains in 3 versus 2 dimensions are longer
Morin p. 143-7
108
How does food web return time influence equilibrium?
1) Long return times (common in longer chains) mean that the system will take longer to return to a stable equilibrium following perturbation
2) If perturbations are long or frequent, systems with long return times might be more prone to extinction
Morin p. 149
109
What is the effect of omnivory on stability?
1) Omnivory decreases stability
2) Omnivory should, however, decrease return times, increasing stability in this sense
Morin p. 150-1
110
Effects of species richness, connectance, and interaction strength on food web stability
1) As any of these factors increase, stability decreases
2) If you increase richness, this decreases connectance and the strength of interactions between individuals?
3) Increased connectance strengthens the interactions which destabilizes the food web
4) Increased interaction strength destabilizes the food web because species are more reliant on one specific prey type (more specialization)
Morin p. 151
111
How does complexity influence food web stability?
Increased complexity increases stability as long as interactions are weak as this yields more generalists and species are less reliant on one specific prey source
Morin p. 152
112
How does productivity influence food web dynamics?
1) Decreasing productivity decreases the number of coexisting species
2) Three level food chains containing a top predator only persisted at high levels of productivity
Morin p. 155-6
113
How does food chain length influence food web dynamics?
Increasing length decreases stability
| Morin p. 157
114
Paradox of enrichment
Dynamics become less stable as systems become more productive and prey become more abundant (more likely to crash because prey will quickly deplete resources)
Morin p. 158
115
Kinds of mutualisms
1) Energetic (trophic in nature)
2) Nutritional (transfer of nutrients)
3) Protective (active or passive defense)
4) Transport (movement of gametes or propagules)
Morin p. 166
116
Obligate mutualisms
1) Neither member of a mutualism can survive without the other
2) E.g., Yucca does not self-pollinate and relies on pollination by Tegeticula moths
3) E.g., Dodos processed seeds of Calvaria plants, which have declined since the extinction of the dodo
Morin p. 167, 171-2
117
Facultative mutualisms
1) Associations are not essential but lead to positive effects on fitness
2) E.g., associational defenses that occur from multiple species forming a large group (better predator defense and foraging information centers)
Morin p. 167, 179
118
Direct mutualisms
One or both species experience a direct benefit, e.g. flowering plants and pollinators
Morin p. 167
119
Indirect mutualisms
1) Positive effects between two species that are transmitted through at least one and sometimes more intermediate species
2) E.g. presence of larval salamanders (which consume large zooplankton) reduce competition for small zooplankton, which allows larval midges (feed on small zooplankton) to increase in abundance
Morin p. 167, 194
120
How does mutualism influence stability
Mutualisms tend to enhance the stability and persistence of highly more elaborate four-species web
121
Predator escape hypothesis
1) Janzen-Connel Hypothesis
2) Better to disperse away from parent plant to avoid pathogens and other "predators" that may inhibit settlement and growth
Morin p. 172
122
Non-equilibrium colonization hypothesis
1) Not all settlement sites are created equal and it is beneficial for seeds to be spread far to ensure some seeds settle in a good environment
Morin p. 172
123
Directed dispersal hypothesis
1) There is an ideal habitat for seeds to be dispersed to to succeed
2) E.g., Mymecochory (production of lipid rich structures in seeds) attracts ants, ants harvest the seed and transport them to the ant nest which minimizes exposure of seeds to predators
3) Obligate mutualism
Morin p. 173-4
124
Plant-defender interactions
1) Ants defend Acacia from predators as they feed on fatty Beltian bodies
2) Also benefits wrens as ants drive nest predators away
3) Obligate mutualism
Morin p. 174
125
Examples of energetic and nutritional mutualisms
1) Ruminants have gut symbionts that digest cellulose and, in return, provide the animal with vitamins and amino acids
2) Mycorrhizal fungi serve as nutrient pumps, facilitating uptake of nitrogen and phosphorous by plants and, in return, receive carbohydrates produced by the plant during photosynthesis
3) Fungal gardening by Littorerea littorina which damage spartina which allows fungus to grow
Morin p. 175-6, 178
126
How does physical stress influence interactions and mutualisms between species?
1) Bertness and Callaway (1994)
2) Increased physical stress increases mutualistic interaction (as highly stress tolerant species can establish and then modify the environment for other species to enter), termed neighborhood habitat amelioration
Morin p. 181-2
127
Indirect effects
1) The influence of one species (the donor) on another (the receiver) travels through a second species, the transmitter
2) Most often results in changes to steady state abundance
Morin p. 187
128
Interaction chain indirect effect
1) When a species indirectly affects others as a consequence of changes in the abundance of an intermediate transmitter species
Morin p. 188
129
Interaction modification indirect effect
1) When a donor species changes the per capita effect of the transmitter on the receiver, without changing the abundance of the transmitter
2) E.g., behavioral changes, changes in per capita effect on species (such as competition coefficients or attack rates)
Morin p. 188
130
Types of indirect effects
1) Apparent competition
2) Indirect mutualism
3) Indirect commensalism
4) Trophic cascades
5) Bottom up indirect effects
Morin Ch. 8
131
Indirect commensalism
1) One species has an indirect positive effect on another species and they receive no benefit or cost
2) Asymmetric competition among resources should yield indirect commensalism
3) E.g., A chiton, Katharina, consumes larger competitively dominant algae, which positively effects limpets which graze on small diatoms that are competitively excluded by dominant algae
Morin p. 195
132
How does feeding specialization effect indirect effects
1) If consumers are generalists, they will compete
2) If they are specialists there should be positive indirect effects
Morin p. 195
133
Bottom-up indirect effects
1) When a low level trophic species influences the abundance of high level species
2) E.g., Wooton and Power, increases in light created increases in algal abundance and increases in carnivore abundance, while herbivore abundance remained unchanged
Morin p. 199
134
Trophic Cascade
E.g. Paine's pisaster experiment
E.g. Mary Power's largemouth bass, minnows, and algae
Morin p. 196
135
Why does herbivore abundance remain the same in bottom-up indirect effects?
1) Because as trophic level 1 increases, so does trophic level 2 (herbivores), which eventually increases consumer/predator abundance, exerting more top-down control on level 2 (limited to odd-numbered food chains)
Morin p. 201
136
How does heterogeneity influence bottom-up effects?
1) Increased heterogeneity among species responses to other species in differing trophic levels increases competition, which breaks down indirect effects and cascades
Morin p. 201
137
Non-additive interactions/Higher-order interactions
1) Additional species to a system influence how focal species interact
2) E.g., the presence of dragonfly larvae changes the behavior of small tadpoles, tadpoles eat less, thereby influencing their growth and survival
Morin p. 203-4
138
Press experiment
1) Density of a species is permanently changed
2) Yields direct and indirect responses
3) Difficult to interpret because of point 2
Morin p. 206
139
Pulse experiment
1) System is allowed to bounce back
2) Yields only direct responses
3) Easier to interpret results
4) Assumes the system has a stable equilibrium it will return to
Morin p. 206
140
How does species richness impact indirect effects
Increased species richness increases the number of indirect effects (Menge 1995)
Morin p. 210
141
How do species connections influence indirect effects?
1) Where species are linked by rigid rods (tight connections among species), a force applied to any one species will be transmitted to many others and yield indirect effects
2) When species are linked by loose connections, a force applied to one species may leave most others unaffected
Morin p. 212
142
Phenology
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Seasonal patterns (abundance or diversity)
Morin p. 217
```
143
Causes of phenological variation
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Broadly:
1) Adaptive responses to interactions with other species
2) Physiological contraints or stochastic events
Specifically:
1) Temporal resource partitioning
2) Tracking of seasonal resources
3) Predator avoidance
4) Facilitation
5) Physiological constraints
6) Chance
Morin p. 219-222
```
144
Temporal resource partitioning (phenology)
1) Species manage to coexist by using the same limiting resources at different times of year
2) Likely when resource levels rapidly recover from utilization, otherwise, first species to deplete the resource would exclude second species
3) E.g., temporally segregated plant species compete less strongly than plants that are actively growing at the same time of year
Morin p. 219
145
Tracking of seasonal resources (phenology)
1) Different species require different resources which vary in abundance over time
2) E.g., oligolectic bees depend on only one or a very few species of plants for the pollen and nectar used to rear their offspring. Flight seasons of the bees coincide with the flowering seasons of the particular plants that they rely on (flights differ in phenology)
Morin p. 220-1
146
Predator avoidance (phenology)
1) Predators and other natural enemies can vary in abundance over time and affect the seasonal abundance of prey
2) E.g., Newts, anurans, and tadpoles. Communities with predators (newts) for a short duration were more similar than communities with predators for a long duration, community composition depended on how long predators and prey interacted within developing communities.
Morin p. 223
147
Physiological constraints (phenology)
1) Phenological patterns are driven by interactions between physiological constraints and seasonal variation in the physical environment
2) E.g., seasonal variation in temperature, photoperiod, or precipitation
3) May be historical artifacts of evolution and may not reflect optimal adaptations to a particular habitat
4) E.g., Breeding phenology of frogs at temporary ponds, a few species can breed in late winter or early spring at nearly freezing temps, while others breed progressively later in the year as temperatures increase.
Morin p. 223
148
Facilitation (phenology)
1) A species that is already present in a community will facilitate the establishment of a new arrival
2) However, we now know that most species that arrive early in community development simply hinder rather than hasten the establishment of others
Morin p. 222-3
149
Priority effects in phenological variation
1) When a species that is already present in a community either inhibits or facilitates other species that arrive in the community at some later time
2) Slight differences in the timing of seed germination are often sufficient to dramatically alter the yield of two competing species
3) E.g., Early dragonfly breeders are larger than late breeders and early breeders suppress abundance of late breeders (based on natural and experimental manipulations), Benke 1978
4) Priority effects typically happen in the absence of predation
5) Priority affects do not need to be tightly linked to seasonal phenological differences among species to affect community structure
Morin p. 224-6
150
Assembly rules
1) Exist if certain sets of species that could be drawn at random from a local species pool fail to coexist at some local level
2) Any influence of early colonists on later ones suggests that community assembly depends on the identity and sequence of arrival of species as communities develop
3) Example derived from theory: Species will successfully invade if R* (resource limitation threshold) is lower than that of a species already in the community, otherwise it will fail to invade because there is not enough of the limiting resource to support its population growth
4) Example derived from theory: The species with the highest P* (Predator density that can be supported by each prey species) dominates in less-enriched habitats , while the species with the lowest R* dominates in more enriched habitats. I.e. the species where one individual supports more predators dominates less-enriched habitats (What?! check this).
Morin p. 229-30
151
Assembly sequences involving specialist consumers
1) Assembly sequence, and not productivity, should determine community composition in systems dominated by specialized predators.
2) E.g. in a system with two prey N1 and N2 (where N1 can survive on less resources) and specialist predators P1 and P2, community invasion sequence would be N1, P1, N2, P2. The mechanism involves a tradeoff between competitive ability with and without predators
Morin p. 230
152
Assembly rules using guild
1) Each guild begins with one species before any guild contains two species, etc.
Morin p. 230-1
153
Assembly rules using food-web dynamics
1) Where multiple alternate permanent sets of species exist, no alternate permanent set will be a subset of any other permanent set
Morin p. 232
154
Catalytic species
Species that cause community changes but do not, themselves, persist
Morin p. 233
155
Humpty Dumpty community states
1) Sets of persisting species which cannot be recreated simply by adding those species at the same time to an empty community
Morin p. 233
156
Community closure
1) When some species losses are irreversible
2) Usually involves a cascade of subsequent extinctions
Morin p. 233
157
Incidence functions
1) Describe the probability that a particular species will occur in a particular community, given some attribute of that community
2) E.g., Jared Diamond created incidence functions for bird species on Bismarck Archipelago and found that the predictive attribute of the community is bird species richness
Morin p. 233
158
"Checkerboard" pattern of species abundance
1) Squares on a checkerboard == habitat patches, or discrete communities
2) Each square is either red or black corresponding to the presence of one or the other species (but never both) of two ecologically similar species
3) I.e., geographic separation of similar species
Morin p. 234
159
Habitat selection as cost/benefit analysis
Habitat selection will depend on the benefits of foraging in a particular place discounted by the risk of mortality in that location
Morin p. 238
160
Evidence for habitat selection
1) Observation that some mobile organisms are found in certain habitats and not others is evidence of this
2) Associations between sets of species and particular attributes of habitat (e.g. variation in foliage height that provide different opportunities fr foraging, nesting, and predator avoidance)
3) E.g., MacArthur found strong relationship between bird species diversity and foliage height diversity
Morin p. 239
161
Drivers of habitat selection
1) Prey availability (Anthopleura anemones occur selectibely in dense patches of the mollusk Mytilus, which are important prey of larger adult Anthopleura)
2) Competitor avoidance (settling inverts discriminate among substrates based on the density of potential competitors that they encounter, e.g. avoidance of the tunicate Botryllus)
3) Predator avoidance (Small, young, aquatic bugs of Notonecta avoid the center of pools where large, cannibalistic adults reside)
*Habitat selection is often a mixture of these factors (E.g., bluegill sunfish don't utilize the most profitable prey patches until they're older and larger to avoid predation)
Morin p. 241-2
162
Graphical theory of habitat selection
1) Animals aim to minimize size-specific mu/g ratio (ratio of mortality to growth)
2) If there is no mortality, individuals should seek to maximize growth and there will be one habitat for all size classes
3) If there is mortality, then there will be habitat switching to minimize mortality but increase growth
Morin p. 249
163
Metapopulations
Collections of populations that are linked by infrequent migration between the spatially subdivided habitats that they occupy
Morin p. 252
164
Interspecific interactions in patchy, subdivided habitats
1) Patchy, subdivided habitat promotes coexistence of competitors
2) Promotes the persistence of predatory-prey interactions that prove to be unstable in undivided habitats
Morin p. 253
165
Competition in spatially complex habitats
1) Promotes the coexistence of competitors in patchy habitats (if strong competitors clump together, this opens up other patches for weaker competitors)
2) Simple subdivision of the environment without intraspecific aggregation is not effective in promoting coexistence
3) Aggregation effects (positive benefit of clumping) requires that patches with dense clumps of one species should not also contain dense clumps of other species
4) Intransitive networks (rock, papers, scissors in interspecific competition) arise when species compete via different mechanisms
Morin p. 253-5
166
Predator-prey interactions in spatially complex habitats
1) Spatial refuges can give prey respite
2) E.g. Huffaker (1958) Showed that subdivided habitats can promote the persistence of predators and prey. In this system, an herbivorous mite fed on oranges, a predatory mite fed on the herbivorous mite and would make the population of the herbivorous mite crash if there was no spatial refuge
3) Huffaker's experiment is similar to Gause's observation that the predator Didinium readily overexploited its prey Paramecium, which led to rapid extinction of either Didinium or both species
4) Spatial heterogeneity yields cyclical patterns in predator-prey dynamics
Morin p. 255-8
167
Habitat fragmentation and dispersal corridors
1) Dispersal corridors affect the properties of metacommunities
2) E.g., Species of microarthropods that persisted in fragments were less abundant than those that persisted in unfragmented patches
Morin p. 266-7
168
Recruitment-limited interactions
1) "Supply-side" Ecology
2) Unusually high settlement would create intense competition among abundant settlers in sites from which predators were removed and could exaggerate the role of predators in thinning settlers and reducing competition for space
3) Highlights the importance of spatial variability in recruitment rates in determining community patterns
Morin p. 269
169
Island Biogeography
1) Fragmented habitat
2) Various patterns emerge:
a) Species-area relationship
b) Equilibrium theory of island biogeography
Morin p. 271-3
170
Species-area relations
1) Number of species found in a particular area increases with the size of an area
2) Found by plotting the log of species richness against log of area
Morin p. 271-2
171
Equilibrium island biogeography
1) May provide an explanation for the species-area relation
2) Assumes that the number of species on an island is a consequence of the dynamic equilibrium that results from the interplay between rates of colonization and extinction
3) Species present == intersection of rate of immigration and rate of species extinction
4) Extinction is more rapid on small islands and immigration is more rapid to near islands
Morin p. 272-3
172
Macroecology
1) Ecological patterns that occur at the largest spatial scales
Morin p. 279
173
Neutral explanations for macroecology
1) Use a set of probabilistic rules to assemble communities from a regional pool of ecologically similar species?
Morin p. 280
174
Equilibrium communities
1) Stable == relatively constant species composition
2) Assumes that community composition represents the stable outcome of interspecific interactions
3) Assumes that community will return to an equilibrium after perturbations
Morin p. 283-4
175
Non-equilibrium communities
1) Fluctuating species composition and extensive variation in population dynamics
2) Prevent an equilibrium from being reached
3) Prevent exclusions of species that might result as a consequence of equilibrium
4) Account for maintenance of diversity within communities y focusing on how disturbances or other processes prevent the exclusion of species that would otherwise occur if communities ever attained an equilibrium
Morin p. 283-4
176
Extinctions
1) Occur when chaotically fluctuating populations move too close to an alternate equilibrium point, which corresponds to the loss of one or more species from the system
Morin p. 289
177
Alternate Stable States
1) AKA bistability
2) Lewontin 1962
3) A community has multiple stable states, not just one
4) Explains differences in composition of communities in otherwise comparable environments
5) E.g. Sutherland's tiles submerged in water, many different compositions arose potentially representing alternate stable states
Morin p. 290
178
Example of long-term stable community
1) Odonate communities in lakes
2) zooplankton abundance in central Pacific Ocean
3) Composition of vegetation in managed grasslands in England
Morin p. 292
179
Equilibrium explanations for diversity
```
Broadly
1) Assume that coexisting species occur in stable equilibrium configurations and emphasize special circumstances that enhance the number of species that can stably coexist
2) Operate by preventing any species from obtaining a competitive monopoly
Specifically
1) Niche diversification
2) Intransitive competitive networks
3) Compensatory mortality
Morin p. 292-3
```
180
Niche diversification (equilibrium explanations for diversity)
1) AKA resource specialization
2) Allows more species to coexist along a particular resource spectrum
3) Packs more but narrower niches into a given range of resources
Morin p. 293
181
Intransitive competitive networks (equilibrium explanations for diversity)
1) Rock, paper, scissors of competition
2) Protects against competitive dominance/competitive monopoly
3) Explains high diversity of microbes that appear to coexist in soils
Morin p. 293-4
182
Compensatory mortality (equilibrium explanations for diversity)
1) When a competitively dominant species suffers disproportionately more mortality than competitively inferior species
2) E.g., enhancement of prey diversity by Pisaster in rocky intertidal systems
3) E.g., Grazing littorina on tide pool algae
Morin p. 294
183
Non-equilibrium explanations for diversity
1) All environments are gradually changing (paradox of the plankton)
2) The storage effect
3) Lottery models
4) Predator-mediated coexistence
5) Intermediate disturbance hypothesis
Morin p. 294-6
184
Paradox of the plankton
1) Paradox: lakes support large number of algal species that all compete for the same resources (CO2, nitrogen, phosphorous, sulfur, etc.), so there is no niche diversification
2) The impact of gradually changing physical conditions within lakes on competition among algae might provide a resolution of the paradox, as no algal species is allowed the time to become competitively superior
3) When the time for competitive dominance (tc) is less than the time required for environment to change so that outcome of competition will be reversed (te), competitive exclusion occurs rapidly
4) When tc = te, no competitive equilibrium is reached
5) When tc > te competitive exclusion is possible (long-lived organisms integrate over short-term environmental fluctuations)
Morin p. 294-5
185
Storage effect
1) Dormant stages or long-lived adults essentially "store" the benefits of good conditions in a variable environment
2) For this to enhance diversity, the environment must vary in a way that each species encounters favorable and unfavorable conditions and conditions favorable for one species must be unfavorable to others
Morin p. 295
186
Lottery models
1) Assumes that openings in habitat are filled at random by recruits from a large pool of potential colonists
2) Species should have low adult mortality, high fecundity, and environmentally dependent recruitment rates so that they can persist until opportunities for recruitment occur
Morin p. 296
187
Non-equilibrium predator-mediated coexistence
1) Caswell's model of "hide and seek" between predator and prey (i.e. prey can escape predation in patchy environment)
2) Increases in the number of cells, dispersal ability of predator, dispersal ability of competitively inferior prey, or time required for competitive exclusion, prolong the existence of multi-species environments
3) Failure to coexist defines the non-equilibrium nature of the model and the mechanisms producing diversity?
Morin p. 261-3, 296
188
Intermediate disturbance hypothesis
1) Frequency and intensity of abiotic disturbance affects patterns of diversity
2) Weak or infrequent disturbance are not sufficient to alter the progress of competitive exclusion and diversity declines
3) Intense of frequent disturbances disrupt the community too much and species are actively excluded, leading to reduced diversity through the loss of species that are particularly sensitive to disturbance
Morin p. 296
189
Community stability and complexity
1) MacArthur and Elton suggested several reasons why more complex communities are more stable than simple ones
2) If top predators feed on multiple prey species (rather than one) there are alternate food sources available if one prey species suffers a crash, ignores whether entire system of populations is more or less likely to be stable as complexity of feeding links increases (May argued that increased food web complexity should decrease stability)
3) Elton argues that two-species interactions (predator prey and competition) oscillate, therefore low diversity yields instability
Morin p. 299
190
Example of relationship between diversity and stability
Hairston
1) Hairston manipulated each trophic level in a three system food web of bacteria, bacterivorous protists and their predators
2) Found inconsistent support for positive effects of diversity on stability
3) Top trophic level failed to act as keystone predator
Lawler
1) Extinctions became more frequent as diversity increased
May
1) Increases in species richness, connectance, or the average strength of interspecific interactions will tend to decrease the stability of an entire system
Morin p. 300
191
Hypotheses for latitudinal gradients in species diversity
1) The tropics support more species because they are more productive, but coral reed communities are relatively unproductive
2) The ages of tropical and temperate habitats increase opportunities for speciation, but paleoecology shows that temperate, polar, and tropical regions have all existed for long periods of time
3) Latitudinal differences in ecological interactions, e.g. a greater intensity of predation in tropical systems might lead to more instances where prey species are able to coexist
4) Disturbance, draws on intermediate disturbance hypothesis, not enough evidence, tropical storms are frequent, however, fire is more common in temperate regions
5) Spatial heterogeneity
Morin p. 301-8
192
Relationship between biodiversity and ecosystem function
1) Sampling/selection effect
2) Complementarity
3) The portfolio effect/insurance hypothesis
Morin p. 308
193
Sampling effect
1) As the number of species in a community increases, it is increasingly likely that the community will contain a species that performs the relevant aspect of ecosystem functioning particularly well
Morin p. 308
194
Complementarity
1) The possibility that different species may use different resources in different ways, and that because of this complementarity a mixture of species may be able to extract more resource from a given environment than any single species
Morin p. 309
195
Portfolio effect/insurance hypothesis
1) Diversity may buffer fluctuations in ecosystem functioning over time in temporally fluctuating environments
2) E.g., Plant biomass in grassland assemblages decreased less in plots with many species
Morin p. 309
196
Succession
1) The process of temporal change in community composition
2) Alternately viewed as a directional process that maximizes various ecosystem processes, or as the simple outcome of various interspecific interactions, which only coincidentally cause changes in ecosystem properties
Morin p. 319
197
Secondary succession
Succession on sites with established vegetation
| Morin p. 320
198
Primary succession
Succession on sterile inorganic substrate
| Morin p. 320
199
Autogenic succession
Driven by processes operating within a particular location
| Morin p. 320
200
Allogenic succession
Driven by factors outside a particular site
| Morin p. 320
201
Seasonal succession
Regular phenology of abundance or activity that occurs without the permanent loss or addition of species from the community
Morin p. 320
202
Cyclic succession
Occurs in special circumstances where a small number of species tends to replace each other over time
Morin p. 321
203
Chronoseries (space for time substitution)
Used to infer successional patterns
| Morin p. 321
204
Initial floristic composition hypothesis
1) Succession at a site is determined largely by the species composition of plant propagules already present when the site is disturbed
2) Only applies to secondary succession
Morin p. 323
205
Resource ratio model of succession
1) Resource supply rates change in some orderly fashion during succession, as a result of consumption, biogeochemical processes, or disturbance
2) Competition for these resources is what drives the replacement process in communities
3) Random or positively correlated changes in two resource supply rates should not produce the orderly changes in species composition that are usually associated with succession (because does not allow for competition or competitive dominance)
4) Negative correlations among resource supply rates over succession will produce trajectories that cut across regions corresponding to dominance or coexistence by multiple species
5) Experimental manipulations of nutrient additions on plant species composition found that nitrogen addition showed that plant biomass increased as light declined, supporting a negative correlation between supply rates of these two resources
Morin p. 330
206
Markov model of species transitions
Morin p. 325
