Lecture 13: Suggested exam questions

From Ricklef's reading (ch 10):

Question 1: Why are some species dispersion patterns clumped, while others are evenly spaced? What are some ecological factors that contribute to these different dispersion patterns?

The dispersion depends on how individuals react to interacting closely with other individuals. Spaced distributions result from competitive interactions between individual (i.e. certain plants competing for water and nutrients in soil, or for light), while clumped dispersions result from tendency for closeness (i.e. social tendencies to form groups, to cluster around resources, or to stay close to parents)

Question 2: What is meant by ideal free distribution? Give three reasons why ideal free distribution is not typically achieved in real-life populations.

Ideal free distribution is achieved when different patches, regardless of quality, have the same value for fitness for individuals.

Question 3: What are the three types of models to describe the spatial structure of populations? Describe how the three types build on each other from the more basic one to the most complex/detailed.

Metapopulation models: describe sets of subpopulations occupying particular habitat patches between which individuals may move.

Source-sink models: builds on the metapopulation model by adding data on quality of habitat, and successful reproduction in high-quality habitats from source populations, to migrations to rescue less successful sink populations in lesser-quality habitats.

Landscape model: builds on the prior models by adding the impacts of habitats on the quality of other nearby habitats and vice versa.

From lecture:

Question 4: Describe the Leslie Matrix and how it is used to understand population dynamics.

A Leslie Matrix models the growth and changes that occur in a population of organisms over a period of time. The model breaks the population down to different age/stage classes, and includes rates of growth and survival (to the next stage class), mortality, and fecundity for each stage class, based on life-history data for the particular species being modeled. The model suggests a steady-state, or stable, age-structure and growth rate. Regardless of the initial population size, N0, or age distribution, the population tends asymptotically to this age-structure and growth rate. It also returns to this state following perturbation. The matrix can be used to understand the effects that different demographic elements have on the population being modeled. It can also be used to derive stable age structure in order to manage populations (in the context of natural resource management— i.e., "How many and at what age should we shoot the bunnies?")

Question 5: What is meant by stable age distribution in a population? What conditions are necessary for it to occur? How can you observe that it has occurred?

A stable age distribution in a population refers to a constant proportion of organisms in each age or stage class, as modeled in a Leslie Matrix. The lambda value does not need to be 1 (the population can still be growing), but the survival and fecundity terms must be constant to achieve this stable age distribution.

Question 6: What is the difference between deterministic extinction and stochastic extinction? Under what criteria will (or could) each of these occur?

Deterministic extinction mainly depends on demographic factors, which directly result in extinction as lambda<1. Stochastic extinction is impacted by stochastic factors, which may not directly bring the population down to the last, but can still cause the extinction even when lambda is equal to or greater than 1, such as when a population is beset by multiple threats.

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