Biology 301 Lecture Outline on Time Lags and Metapopulations

A. Time Lags

1. Populations often show overshoots of the carrying capacity or oscillations around K

2. The logistic equation will produce oscillations if time lags are introduced

3. Time lags are where the population growth rate is according to a population density prior to the current density of the population

4. The relative values of r and the time lag determine whether damped oscillations or stable oscillations are observed

5. Nicholson blowfly experiment is the classic example

a. Unlimited food for the adult population

b. Food limitation in the larval phase


B. Spatial Dynamics

1. Populations can be divided into discrete spatial units

2. Discreteness is a function of the migration term

3. Extinction is a function of population size

4. Populations divided into discrete spatial units may show very different temporal dynamics


C. Metapopulations

1. Almost all populations are fragmented to some degree and thus have patch structure

2. Most ecological processes are strongly affected by the degree to which populations are subdivided

3. Occupation of presumably habitable sites are affected by both ecological processes such as local mortality rate as well as the size of the site and its distance from other sites

4. Metapopulation is a population comprised of subpopulations which are sufficiently distinct that those subpopulations can go extinct when the other subpopulations do not; thus, the metapopulation persists as a balance between extinction and colonization of the subpopulation sites.

5. The overall population may be stable but the subpopulations are not.

6. Local populations that are part of a metapopulation are likely to be unstable in their dynamics

7. Maintenance of genetic diversity within a metapopulation depends on the interplay of patch size, colonization rates, and extinction rates. Those determine such components as effective population size, relative importance of genetic drift vs natural selection, all of which we will discuss next.