Extinction Risk
What is inbreeding depression, and how is it related to conservation?
Inbreeding depression is the reduced fitness/survival of a population due to breeding with close relatives. It is usually most relevant in small populations (like those of endangered spp) where many of the individuals are related, and increases the likelihood of offspring being homozygous for/expressing deleterious alleles.
In describing a species niche, how many axes are typically used?
MANY – not necessarily limited to what we can plot (2 or 3 axes). Hutchinson described a species niche as being n-dimensional.
What do the alpha and beta variables in Lotka-Volterra equations represent? What does it mean when these variables are greater than 1?
Alpha and beta are examples of competition coefficients, which measure how strong competitive interactions are. If the competition coefficient is greater than 1, interspecific competition is stronger than intraspecific competition.
What is the difference between primary and secondary succession?
Primary occurs in habitats where life previously did not occur, occurring over long timescales. Secondary usually follows a disturbance, on a shorter timescale, when communities recolonize disturbed habitat.
If a predator and prey population are undergoing neutrally stable oscillations, how do small versus large perturbations from equilibrium affect population dynamics?
Small perturbations from equilibrium dampen amplitude of population sizes, whereas large ones increase amplitude. Sometimes this leads to perturbations being too large and crashing one population, which could lead to the crash of the other.
Describe Allee effects, and when do we usually observe them?
Inverse density dependence; population per capita growth rate decreases with population size; usually seen in small pop sizes
Do population growth rates tend to change across space? Why or why not?
Yes – the conditions a population experiences in a particular location situates it in different parts of it’s fundamental niche, which affect overall growth and performance.
What did Joe Connell’s 1961 experiment demonstrate in the rocky intertidal?
Evidence for competitive exclusion, and niche limitation based on competitive dynamics. After removing lower elevation barnacle species, the higher elevation barnacle species spread to lower elevations previously occupied, indicating its niche was being limited by competitive interactions between the two species.
What is a stable state distribution in the context of ecological succession? At the Indiana Dunes, where would we find this state, if at all?
The equilibrial frequencies of each ecological state in a given community. Usually called the ‘climax community’. We would likely find this at the southern-most end of the Indiana Dunes, which remain less disturbed than other parts of the park.
Describe two examples of indirect effects in food webs, and describe where they would appear in the following hypothetical food web:
Apparent competition: when populations exhibit dynamics that look competitive, but are really the result of having the same predator. Here, that would look like Plant 1, 3, and 4 having ‘competitive’ dynamics that are really driven by herbivore 1.
Interaction modification: when the behavior of one species affects the interaction between two other species. For example, the presence of the insectivore will alter herbivore 1’s behavior such that it hides when the insectivore is around. This will reduce overall feeding time and thus the strength of the interactions with potential food plants (especially if they’re in open areas where insectivores are more likely to see them, etc).
Describe how the species-area relationship (S = cAz) and metapopulation persistence (Px = 1 - (pe)x) change with respect to habitat loss.
A declines => S declines; x declines => Px declines
What types of experiments can we do to test for local adaptation? Explain how it would be done.
Common garden experiments – an example is the plant transplant experiment that isolated clones of the same species found in nature at different elevations, grew them at each elevation, and tracked growth for each plant. This showed whether the populations from a given location grew best at their native elevation, or if populations grown in their native elevation outgrew those from other elevations.
What do we add to the logistic growth model to yield the Lotka-Volterra competition model? Do both incorporate density dependence?
We add in the competition coefficients alpha and beta, reflecting the impact of Spp1 on Spp2 and Spp2 and Spp1, as another factor that is modulating rN. Both include density dependence, reflected in both as N/K.
Hypothetically, what degree of disturbance is optimal for maximizing species diversity in a given community? Why?
Intermediate amounts of disturbance are best. Low disturbance favors strong competitors, since succession has theoretically had the longest time to happen, and this means these strong competitors will outcompete other species. High disturbance favors only strongest colonizers, not allowing for weaker ones; resets occur so frequently that community membership cannot be built up.
Are Lotka-Volterra models of competition or predator-prey dynamics more likely to be stable? Why?
LV predator-prey are more likely stable; unlike competition models, which have one equilibrial point, the range of mathematical space in which equilibrium can occur (in the style of neutral oscillations) is much greater.
What is the difference between demographic stochasticity and environmental stochasticity?
DS: Changes in demographic outcomes that are not caused by vital rates (deterministic).
ES: Environmental fluctuations can alter (depress) vital rates of population, either due to stochastic or deterministic variation
Name three reasons why species ranges don’t continue expanding forever (especially since we know local adaptation at range edges is possible).
Gene flow from populations at the center to edge of the range occurs, making it more difficult for edge populations to continue accumulating advantageous/adaptive genotypes/phenotypes
Edge populations tend to have reduced genetic variation, which makes it harder to adapt
Tradeoffs often occur between phenotypes that are good for adaptation and phenotypes that are good for maintaining population viability
What do zero net growth isoclines (ZNGIs) represent? How do we find the function describing their behavior?
ZNGIs show us the possible values N1 and N2 can take where net growth (dN/dt) of the population is zero. By setting Lotka-Volterra differential equations to 0 and simplifying, we get the functions describing their behavior (linear): N(hat)1 = K1 - alpha*N2, N(hat)2 = K2 - beta*N1
When predicting (projecting) the future of succession in a given community, what information is stored in the matrix, and what information is stored in the vector? (remember: s(t+1) = As(t))
The matrix holds information about probabilities of transitioning between ecological states, which can be species composition, functional groups, habitat types, etc. The vector holds the measured values of the frequency of each of these ecological states.
The Lotka-Volterra models of competition and predator-prey interactions have similar structure but different formulations. Writing out the differential equations for LV predator-prey models on the board, describe what aspects are different from the competition model.
(see slides for equations!)
In competition models, both species suffer (-,-), and are based on logistic models of population growth (saturating based on carrying capacity K). In predator prey models, only one species suffers (-,+), and are based on exponential models of population growth. In this case, initial conditions drive the oscillations that can become equilibrial (stable), whereas competition models typically have one fixed equilibrium point (stable coexistence) or cases of competitive exclusion.
Describe the process through which we do population viability analyses (PVA), and some examples of the output variables we can expect to calculate.
Stochastic projections: we take matrices of population vital rates at snapshots in time, randomly assign them to future years we’re interested in learning about, and map their trajectories. From these projections, we can learn about the distributions of possible future population sizes, probabilities of extinction, or predicted time to extinction
How do we test whether a species is limited by dispersal or niche breadth?
A species limited by dispersal will be viable outside of its native range; a species limited by niche breadth will not be. By conducting beyond-range transplant experiments, we can test how viable transplanted populations are to areas outside of the range. We can also measure the vital rates of different populations ranging from the center towards the edges of the species range, and after stochastic projections, estimate lambda and compare them.
What are the four possible outcomes of two species competitive dynamics? Please draw the graph indicating the isoclines for Spp1 and Spp2 at a stable equilibrium (include axis labels!)
(See pic in slides!)
Notice: ‘winning’ situations have ZNGIs with no crossing and winning species on top. Equilibrial outcomes are either stable or unstable, with unstable dynamics having carrying capacities higher on each species’ respective axis
Describe the three models of ecological succession.
Facilitation: The presence of first-arriving species encourages colonization from later-arriving species, usually by ameliorating environmental stress/building habitat
Inhibition: First-arriving species prohibit future competitors from colonizing, usually from dominating and monopolizing resources
Tolerance: Regardless of arrival time, species ‘tolerate’ each other and are indifferent to the environment
Draw the phase diagram for Lotka-Volterra predator-prey dynamics, labelling two different cases of stable equilibria.
(see slides for graph!)
One would be point at the middle where numbers of each stay the same, and others would exhibit stable oscillations.