BIOL 2010 Lecture Notes - Exponential Growth, Logistic Function, Polyploid
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Chapter 54 – Population Ecology
54.1 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
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
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.
54.2 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.
54.3 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
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.
An environment can support no more than a certain number of individuals of any particular
species per unit of area environmental carrying capacity, K. It is determined by the
availability of resources as well as by diseases, predators and sometimes social interactions.
Growth of a population typically slows down as its density approaches the environmental carry
capacity b/c resource limitations and the activities of predators and pathogens lower birth rates
and increase death rates logistic growth.
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