Population Ecology Questions:

1. Why are there many or few individuals in a population?

2. Why do the numbers of individuals in a population change (or not change) over time or space?

3. Why does a population contain many or few young (or small) individuals in relation to the number of older (or larger) individuals?

4. What is the effect of the proportion of young/small individuals on the rate of population growth or decline?

5. How does a population persist in spite of the fact that each individual will die relatively soon?

6. What is the probability that a population in a stochastic (i.e., random) environment avoids extinction between now and a specified future time?

7. How do human activities affect the probability of extinction of populations of other species, and how can that probability be reduced?

8. How do interactions with other species (competitors, predators, pathogens, mutualists) affect the dynamics of a focal population?

Newton’s First Law:

Every body remains in a state of repose or uniform, rectilinear movement unless other bodies act on it.

“The First Law of Population Dynamics”:

Every population remains at a constant PER-CAPITA rate of growth or decrease unless other forces act on it.

Some “other forces”:

1) Environmental stochasticity, or variability in the rate of population growth YEAR TO YEAR due to variability in precipitation, temperature, etc. (including “catastrophes” and “bonanzas”)

2) Demographic stochasticity, or variability in reproduction or survival among individuals IN THE SAME YEAR.

3) Density dependence, positive or negative, generated by interactions with conspecifics or individuals of other species

4) Variability in population structure (i.e., the distribution of individuals of different ages or sizes)

5) Movement or dispersal

6) Changing densities of interacting species

Brown (or “Grizzly”) BearUrsus arctos

Yellowstone National Park(Wyoming, Montana, Idaho)

Frequent human-bear contact in this isolated population

Before 1973, bears counted at trash dumps

After dumps closed, aerial census of females with new cubs

http://www.fws.gov/mountain-prairie/species/mammals/grizzly/workshop_summary_final08312005.pdf

1988 Yellowstone Fires

Did they affect the Grizzly Bear Population?