# BIOL 4503 Lecture Notes - Exponential Growth, Founder Effect, Introduced Species

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How Do Ecologists Study Populations?

•A population consists of the individuals of species within a given area.

•The members of a population are distributed over space, and they differ in

age and size.

•The age distribution of individuals are spread over the environment describe

its population structure.

•The number of individuals of a population per unit of area is its population

density.

•The structure of a population changes continually because demographic

events are common occurrences.

Population densities can be estimated from samples

•Estimating population densities is easiest for sedentary organisms.

•Counting mobile organisms is much more difficult because individuals move

into and out of census area. (write equation here).

Birth and death rates can be estimated from population density data

•(Write equation here).

•Individuals born at the same time cohort.

•The number of a population still alive at a given period of time in the future

survivorship.

How Do Ecological Conditions Affect Life Histories?

•An organism’s life history describes how it allocates its time and energy

among the various activities that occupy its life.

•Ecological interactions influence the evolution of life histories.

What factors Influence Population Densities?

All populations have the potential for exponential growth

•All populations have the potential for explosive growth. As the number of

individuals in a population increase, the number of new individuals added per

unit of time accelerates (even if the rate of increase is expressed on a per

individual basis remains constant).

•If birth and deaths occur continuously and at constant rates, a graph of the

population size over time forms a continuous upward curve exponential

growth.

•(Write equation here).

•The difference between the average per capita birth rate and the average per

capita death rate of a population produces the net productive rate of a

population.

•The highest possible value for the net productive rate is called rmax, or the

intrinsic rate of increase, expressed: (write equation here).

•For very short periods, some populations may grow at rates close to the

intrinsic rate of increase.

Population growth is limited by resources and biotic interactions

•No real population can maintain exponential growth for very long. As a

population increases in density, environmental limits cause birth rates to

drop and death rates to rise.