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Transcript of Population Dynamics
How Populations Grow
Human Population Growth
Organisms enter a population in 2 ways:
Organisms leave a population in 2 ways:
Model 1: Exponential Growth
Model 2: Logistic Growth
The growth of a population continues indefinitely.
Assumes no resource limitation.
Can be described by:
change in number of individuals (
change in time (
: the "
per capita rate of increase
r = population growth under ideal conditions
As long as (r) is a positive value, a population will continue to increase at an exponential rate.
Higher (r) values will lead to faster rates of increase.
if (r) is 0, the population will not increase or decrease.
if (r) is negative, the population will decrease.
The growth of a population decreases as the population approaches the "
) of the environment.
Models resource limitations.
The effect of (K) on (r) becomes greater as (N) approaches (K)
How are real populations structured?
How do real populations grow?
How does evolution effect life history traits?
How does the environment affect population growth?
Measuring Population Size
It can be difficult to estimate population size accurately.
Capture and mark members of the population.
Recapture members of the population.
Number of marked individuals Recaptured marked individuals
Total population size Total recaptured individuals
Individuals tend to be distributed in three major patterns:
Demographics: The study of a population's vital statistics and how they change over time.
Demographic Data can be arranged in tables (e.g.
), or graphs (e.g.
Three major types of survivorship curves in real populations:
Typically occurs in small populations, well below the carrying capcity of the environment.
Much more common. Typically populations oscillate around the carrying capacity.
Life History Traits
Any trait that affects an organism's life table.
Costs and benefits of all adaptations.
: Produce a lot of offspring, once
: Produce a few offspring, repeatedly
Number of babies varies inversely with amount of parental care
Selection for traits that maximize reproductive success at low-population densities
Selection for traits that maximize reproductive success at high population densities
The effect of population density on population growth
Density Dependent Population Regulation
The underlying root of all
Historical Human Growth Rate
The human population has been in a period of accelerated exponential growth since the industrial revolution...
...that growth rate is slowing
The decrease in growth rate is not uniform across the globe.
As countries industrialize, various changes in demographics occur (the "
A comparison of the exponential and logistic growth models
N = ~1,100
The Agave Plant: Semelparous
Elephants (and all mammals): Iteroparous
Data showing parental survivorship as a function of brood size in kestrels
Human Population Growth
The global carrying capacity for humans is unknown
Human Population Distribution
Human Fertility Rate
7 - 8 Children
6 - 7 Children
5 - 6 Children
4 - 5 Children
3 - 4 Children
2 - 3 Children
1 - 2 Children
0 - 1 Children