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
•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
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
•(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
•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.