**Population Dynamics**

**How Populations Grow**

**Theory**

**Reality**

**Human Population Growth**

Organisms enter a population in 2 ways:

Birth

Immigration

Organisms leave a population in 2 ways:

Death

Emmigration

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 (

dN

)

change in time (

dt

)

r

: 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 "

carrying capacity

" (

K

) 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

Population Distribution

Population Demographics

It can be difficult to estimate population size accurately.

"

Mark-Recapture

"

Capture and mark members of the population.

Release them.

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:

Clumped

Uniform

Random

Demographics: The study of a population's vital statistics and how they change over time.

Demographic Data can be arranged in tables (e.g.

life tables

,

reproductive tables

), or graphs (e.g.

survivorship curves

).

Three major types of survivorship curves in real populations:

Exponential Growth

Typically occurs in small populations, well below the carrying capcity of the environment.

Logistic Growth

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.

Reproductive stategies

Parental Care

Semelparity

: Produce a lot of offspring, once

Iteroparity

: Produce a few offspring, repeatedly

Number of babies varies inversely with amount of parental care

r-Selected

vs.

K-Selected

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

Competition

Predation

Territoriality

Waste Accumulation

Intrinsic Factors

Disease

The underlying root of all

anthropogenic

ecological problems

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 "

demographic transition

")

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

"Age-Structure Pyramids"

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

max