Population Ecology

I. Introduction; What are characteristics of a population?

A. Definition

-groups of individuals of a single species that occupy the same general area.

-use similar resources; influenced by similar environment; breed and interact

-characteristics of a population can change with time through natural selection (evolution)

B. Demography

1. Definition

2. What factors influence population size?

3. Life Table

example: ground squirrel

4. Survivorship Curve

Type I

Type III

Type II

II. Modeling Population Growth

1. The potential for population growth is very great

2. Ideal (Exponential) Population Growth

a. A Model for microorganisms in culture

N₀ = initial number of individuals

N = number of individuals after a given number of generations

So, after 1 generation (if populations doubles):

N = N₀ X 2

After two generations:

N = N₀ X 2 X 2

After "x" generations:

N = N₀2^x

The Exponential Curve

b. How do you calculate the rate of growth? (without calculus)

-Convert exponential growth equation to linear form:

Take natural log (ln) of both sides

ln N = ln N₀ + x ln2

x (number of generations) = t/g (t = time taken for x generations; g = time for one generation)

Substitute

ln N = ln N₀ + (t/g) ln2

ln N = ln N₀ + (ln2/g) t

ln2/g = growth rate = r (constant based on maximum growth rate of the population)

So,

ln N = ln N₀ + rt  (Growth Rate Equation for Exponential Growth)

3. Non-Ideal or Limiting (Logistic) Population Growth

a. What happens when resources become limiting?

carrying capacity (K)

b. What is the effect of K on a population growth curve?

-sigmoidal (J) curve (logistic model)

-examples of logistic growth in nature

Does logistic growth always apply?

4. Computer simulations of growth

Exponential growth

Logistic Growth

What is the impact of declining carrying capacity on the initial growth rate of a population showing logistic growth?

What effect will  higher birth rate have on the final population size?

III. Human Population Growth

1. Human population growth is exponential

2. Will the growth rate of the human population slow down or reach zero (ZPG)?

a. Demographic transition

births>deaths - population grows

-what is the demographic transition?

b. Age structure

-age structure pyramids allow a prediction of future population growth rate

Human population growth data: