Ecology 2

Question 1

Five fundamental types of species interactions

Answer 1

1) Competition (-,-)
2) Predation (-,+)
3) Mutualism (+,+)
4) Commensalism (o,+)
5) Ammensalism (o,-)

Question 2

What is a niche?

Answer 2

1) Role organism plays in environment
2) Role can be determined by measuring all of an organism’s activities and requirements
(Hutchinson 1957)

Question 3

What are the two types of niches?

Answer 3

1) Fundamental: niche space is determined by environmental factors and resource requirements (absence of other organisms)
2) Realized: niche space determined by combined abiotic and biotic factors (presence of other organisms)

Question 4

What are the two types of competition?

Answer 4

1) Interference (direct competition, e.g., aggression, e.g., territoriality)
2) Exploitative (indirect competition, resource competition, e.g. sessile organisms)
3) Apparent competition (indirect competition, presence of two non-competing species increases the overall predation pressure experienced by both)

Question 5

Competitive Exclusion Principle

Answer 5

1) Species occupying the same niche outcompete each other

2) Leads to resource partitioning

Question 6

Examples of non-overlapping spatial or temporal distributions based on niche partitioning

Answer 6

1) barnacles and mussels are structured by tidal height

2) Black and yellow rockfish and gopher rockfish are structured by reef depth

Question 7

Competitive release

Answer 7

1) Difference in distribution when competing species are separate and together
2) E.g., In the absence of mussels, barnacles dominate and vice versa

Question 8

Individual responses to competition

Answer 8

1) Behavioral (feeding rates, foraging distribution, e.g. )
2) Physiological (growth rate, reproductive rate, e.g. cladoceran crustaceans grow at different rates when they are competiting)
3) Morphological (body size, biomass, e.g. increased petiole elongation due to increased competition intensity for lite in Trifoluim repens)

Question 9

Population responses to competition

Answer 9

1) Abundance (density)
2) Distribution (zonation)
3) Demographic rates (population growth)

Question 10

Character displacement

Answer 10

When differences among similar species whose distributions overlap geographically are accentuated in regions where the species co-occur, but are minimized or lost where the species’ distributions do not overlap (e.g., Darwin’s finches)

Question 11

Predation

Answer 11

Consumption of one organism (prey) by another (predator), which by definition, occurs between organisms on different trophic levels

Question 12

Predatory effects on prey

Answer 12

1) Direct effects (direct losses, death of individuals, mortality rate of population)
2) Indirect effects (behavioral, physiological, and morphological)

Question 13

Individual responses to predation

Answer 13

1) Behavioral (e.g. avoiding certain habitats until a given size is reached, frogs)
2) Physiological
3) Morphological (e.g., Daphnia produce armor in predator presence)
4) Mortality

Question 14

Population responses to predation

Answer 14

1) Abundance (density)
2) Distribution (zonation)
3) Demographic rates (population growth)
4) Dynamics and persistence

Question 15

Example of predator-mediated competition

Answer 15

In the absence of a predator, barnacles out-compete mussels and expands distribution down into the mid intertidal

Question 16

Complex dynamics resulting from predation

Answer 16

1) Apparent competition (gastropods and bivalves do not compete but increase predator abundance)
2) Trophic cascade

Question 17

Oksanen/Fretwell model

Answer 17

As productivity increases, food chain length also increases

Question 18

Structure of odd and even numbered food webs

Answer 18

1) Odd number of trophic levels should have high plant abundance because consumers (herbivores) are kept in check by predators
2) Odd number of trophic levels means that odd-numbered levels are controlled by competition and even-numbered levels are controlled by predation
3) Even number of trophic levels should have low plant abundance because plants are herbivore limited
4) Even number of trophic levels means that odd-numbered levels are controlled by predation and even-numbered levels are controlled by competition

Question 19

Mutualism/commensalism

Answer 19

1) Occur between or within trophic levels (but more often between)
2) Example of mutualisms: pollinators
a) can be obligate (pollinators)
b) can be facultative (cleaner fish and parasitized host)
3) Example of commensalisms: facilitation

Question 20

Community metrics of diversity

Answer 20

1) Species richness (# species in community)
2) Species composition (identity of species that constitute community)
3) Species diversity (species richness and relative abundance)
4) Species evenness (relative similarity of species abundance in a community)

Question 21

Spatial scales of species diversity

Answer 21

1) Alpha (within habitat)
2) Beta (between habitat)
3) Gamma (total diversity in a landscape)

Question 22

Mechanisms of diversity through community stability

Answer 22

1) Multiple weak interactors create greater community stability than few strong interactors (e.g. trophic cascade versus complex food web)
2) Complementarity refers to greater performance of species in mixture than performance alone (e.g. facilitation, differential resource use among multiple species)
3) Functional redundancy can contribute to community stability by compensating for relative vulnerability and loss of species
4) Identity effects, e.g. presence of a keystone predator

Question 23

Metacommunities

Answer 23

A set of interacting communities linked by the dispersal of multiple, potentially interacting species

Question 24

Maintenance of species diversity

Answer 24

1) Ecological succession
2) Predation
3) Disturbance

Question 25

Early successional species

Answer 25

1) r-selected
2) good at dispersing to and colonizing newly disturbed sites
3) grow rapidly
4) are out-competed

Question 26

Late successional species

Answer 26

1) K-selected
2) poor at dispersing to and colonizing newly disturbed sites
4) grow slowly
5) out-compete early species

Question 27

Models of succession

Answer 27

1) Facilitation: early species modify the environment and make it more suitable for later species, but modified environment is not good for early species and they become outcompeted
2) Inhibition: Early species inhibit later species from colonizing, and secondary colonizers only come as early species die and then outcompete primary species
3) Tolerance: No interactions, earlier species are quick to colonize and later species ‘tolerate’ earlier species and lower resource availability
(Connell and Slatyer 1977)

Question 28

Losses of diversity

Answer 28

1) Interspecific competition (e.g. competitive exclusion of chthamalus by balanus from mid-intertidal OR competitive exclusion of barnacles and algae by mussels in mid-intertidal of exposed sites)

Question 29

When can release from interspecific competition occur?

Answer 29

1) Resources are limited
2) Reduction in populations through other interactions (e.g. predation) to levels where resources are not limiting
3) Disturbance interrupts succession sequence

Question 30

Mechanisms that reduce populations, yielding release from interspecific competition

Answer 30

1) Intraspecific competition > interspecific competition (e.g. allelopaths that kill conspecifics)
2) Intransitive networks (e.g. Sinervo’s lizards)
3) Compensatory mortality (mortality is greater in competitive dominant because it is more abundant)
4) Gradual change (competitive rank varies with changing environmental conditions, e.g. Hutchinson’s paradox of the plankton)

Question 31

How does predation maintain species diversity?

Answer 31

1) Compensatory mortality: generalist predator eats prey as they are encountered (like a disturbance)
2) “Switching” predator: predator preference switches with relative abundance of prey species
3) Keystone predation: predator prefers competitive dominant species and is a specialist on competitive dominant

Question 32

Example of ‘switching’ predator

Answer 32

Barnacle and mussel coexist with presence of predatory snails, Morula prefers mussels, and Acanthina prefers barnacles, but both switch

Question 33

Example of keystone predation

Answer 33

1) Pisaster is a mussel specialist, and mussels can outcompete other intertidal species

Question 34

Intermediate disturbance hypothesis

Answer 34

1) Species diversity is greatest at intermediate levels of disturbance
2) Disturbance interrupts successional sequence by creating patches of different ages (different states of succession)
3) In the absence of disturbance, succession leads to climax community characterized by monospecific stand of competitive dominant (yields low diversity)
4) A intermediate levels of disturbance, there is a mix of patches with climax, early-fugitive, and middle succession
5) E.g. Sousa’s intertidal boulders, early had Ulva, middle had three species, late had one species
6) E.g., Boulders of different sizes roll at different frequencies, medium boulders had the highest species diversity

Question 35

Community stability and components of stability

Answer 35

A community which, when perturbed, returns to pre-perturbation state (with regard to relative abundance of species)

Components

1) Resistance: community or population persists, unaltered when exposed to a source of perturbation
2) Elasticity: how fast a population or community returns to equilibrium
3) Amplitude: magnitude of perturbation that a population or community can return from
4) Resilience: community or population returns to equilibrium following perturbation

Question 36

Deterministic models of stability

Answer 36

Have predictable consequences from a given set of ecological processes (e.g., predictable effects of predation (keystone), competition (climax), mutualisms)

Question 37

Stochastic models of stability

Answer 37

Have unpredictable consequences because of varying effects and occurrence of processes (e.g. larval supply and resource availability)

Question 38

How do post-settlement processes affect communities and populations

Answer 38

1) Community level (maintenance of diversity, patterns of stability)
2) Population level (vertical patterns of zonation and abundance, horizontal patterns of species abundance)

Question 39

What individual life history responses affect population and community level responses

Answer 39

1) Mortality
2) Growth
3) Fecundity
4) Morphology
5) Behavior

Question 40

Example of how environmental variation influences morphology

Answer 40

Shell aspect is lower with exposure to larger waves (limpets)

Question 41

Examples of allocation of resources in response to predators

Answer 41

1) If predation on smaller individuals occurs, individuals will shift energy to growth
2) If predation on larger individuals occurs, individuals will shift energy to reproduction at younger, smaller stages
E.g. Menidia reproduce younger and smaller in response to fishing

Question 42

Examples of behavioral responses to predators

Answer 42

Sea urchins change their foraging behavior in response to food availability

Question 43

Examples of morphological responses to predators

Answer 43

1) Chthamalus has more conic shape further from crevices (compared to bent shape close to crevice)
2) Also more Chthamalus further from crevice
3) Acanthina causes distribution because of limited foraging distribution from cracks and the differential vulnerability of bents and conics (conics more vulnerable to Acanthina)
4) Conics persist, however, because they are better competitors than bents

Question 44

What are characteristics of equilibrium hypotheses?

Answer 44

1) Involve settlement and post-settlement processes
2) Stress biotic interactions
3) Mostly competition based (e.g., competitive exclusion principle)
4) Community structure and dynamics are predictable
5) Because they involve deterministic biotic processes
6) Predictable return to pre-perturbation states

Question 45

List of equilibrium hypotheses

Answer 45

1) Niche diversification hypothesis
2) Compensatory mortality
3) Predation hypotheses

Question 46

Niche diversification hypothesis (as equilibrium model)

Answer 46

Assumptions:
1) Competition based
2) Resource partitioning
3) Assume perturbation does not alter resource availability
Prediction:
1) Total number of individuals and total number of species limited by resources
2) Relative abundance of species determined by relative niche availability
3) Predictable composition and relative abundance

Question 47

Compensatory mortality (as equilibrium model)

Answer 47

Assumptions
1) Competition based
2) Disturbance removes most abundant species
3) Assume perturbation does not alter resource availability
Prediction:
1) Inverse relationships in species abundances
2) Most abundant species at any time suffers disproportionate absolute mortality

Question 48

Predation hypotheses (as equilibrium model)

Answer 48

Includes:
1) Compensatory mortality
2) Predator switching
3) Keystone predation
4) Competition for refuge from predation
5) Density dependent effects of predators on prey species
Assumptions:
1) Predator causes disproportionately higher absolute mortality in most abundant prey species (competitive dominant species)
2) Induces competition or otherwise regulates prey populations
3) These allow persistence of rare species or inferior competitors
Predictions:
1) Inverse relationships of species abundance
2) Most abundant species at any time suffers disproportionate absolute mortality

Question 49

Predation hypothesis predictions for recruitment patterns

Answer 49

1) Compensatory mortality and switching predicts that differences in recruitment diminish over time as numbers converge
2) Induced competition for refuge predicts a pattern similar to niche diversification
3) Regulation of prey populations separately via density dependent predation leads to predictable relative abundance of adults

Question 50

What are characteristics of non-equilibrium hypotheses?

Answer 50

1) Various processes can be involved: competition, predation, disturbance, and recruitment limitation
2) Relative and total abundance fluctuates unpredictably
3) Species composition is unpredictable
4) Species composition and abundance does not return to pre-perturbation state

Question 51

Types of non-equilibrium hypotheses

Answer 51

1) Intermediate disturbance hypothesis
2) Recruitment limitation hypothesis
3) Lottery hypothesis
4) Lottery model/Storage effect
5) Gradual change hypothesis?
6) Pluralistic approach

Question 52

Recruitment limitation hypothesis

Answer 52

Assumptions:
1) High mortality of pelagic larvae limits number of recruits to benthic populations
2) Larval supply limits recruitment below that which is required to saturate resources
3) No competition, so mortality is density-independent
Predictions:
1) Total numbers and relative abundance fluctuates with variable larval supply

Question 53

Lottery hypothesis

Answer 53

Assumptions:
1) Competition based
2) Larval pool saturates resources (opposite of assumption for recruitment limitation hypothesis)
3) No resource partitioning
4) Random chance controls likelihood of acquiring resources
5) Likelihood of settlement is equal to relative abundance in larval pool
Predictions:
1) Unpredictable as to what species will recruit to any location at any time
2) Maximum total abundance across all species determines K
3) Relative abundance of species fluctuates unpredictably, including after perturbation

Question 54

Lottery model/Storage effect

Answer 54

Assumptions:
1) Competition based
2) Same assumptions as lottery hypothesis
3) Relative recruitment success of species changes through time
4) Variable success due to variation in larval production, planktonic conditions, and settlement conditions
5) Species persist through bad recruitment periods and “Store” recruitment events in extended lifetime
Predictions:
1) Same at lottery hypothesis

Question 55

Gradual change hypothesis

Answer 55

Competitive rank varies with changing environmental conditions, e.g. paradox of the plankton

Question 56

Pluralistic approach

Answer 56

Assumptions:
1) Probably a combination of several non-equilibrium hypotheses
2) Varies in importance over scales of space and time
3) Involves orthogonal manipulations of competition, predation an disturbance
Predictions:
1) Relative importance of any model is determined by whether recruitment is modified by post-recruitment processes

Question 57

Example of alternative stable states

Answer 57

1) With a shift from predator-dominated to prey-dominated community, atlantic cod can’t recover because of predation on their larvae, and competition with their larvae by their prey (sprat and herring)
2) Climate change facilitates invasion of sea urchin and transition from forest to barrens
3) Only large lobsters can control sea urchin invasion, but large lobsters removed by fisheries, so with presence of lobsters we get kelp forests but in absence of lobsters we get urchin barrens