ECOLOGY

Features that determine the future of a population:

• Population size- the # of individuals in a population

• Population density- the # of individuals in a given area

• Dispersion-the way individuals are arranged in space

A population refers to all the members of one species, in one place at one time.

How members of a population are arranged in a given space.

DISPERSION:

Patterns of dispersion Individuals in a population may be

distributed according to 3 basic patterns of dispersion– Random– Uniform (also known as Even)– Clumped

Random Dispersion

Scattered, not uniformWhy?

Environment is uniform Individuals are solitary

They live independently

Pine trees in a random distribution

Uniform Dispersion

About equal distance apart, forming a patternWhy?

Resource competition

Birds in an even distribution

Clumped Dispersion

Grouped in some places, absent in others irregular pattern

Why? Resources are patchy Search for food

Buffalo in a clumped distribution

Why do you think scientists study

population dispersion? How individuals are arranged within a population can affect...

Reproduction

Protection(from

predators)Hunting patterns

(if carnivorous)

Can you name the 3 patterns of dispersion?

Clumped

Uniform

Random

Scientists study the population density because it helps determine how the individuals of a population interact.

Reproduction

Protection

Eating patterns

Social hierarchies, if any

Which population of wildebeest has the greatest population

density?

An extremely dense population of wildebeest:

Modeling Population growth

Population success = reproduction of species

We can study how and why the number of individuals change over time

Populations grow when more individuals are born than die in a given period. A simple population model describes the growth rate as shown:

(r) = birthrate – death rate

A small # of the youngest-decrease

Middle age population is constant, secure, not changing

The older population decreases, faster

Describe what is happening to the population in this graph

AGE

# o

f In

div

idu

als

Exponential Growth

Exponential growth-the rate of population growth stays the same and the population size increases steadily.

This model displays a J-shaped curve which indicates a steady increase of population size.

What if the population size kept growing and growing and...

carrying capacity (K)- the population size that an environment can sustainWhat factors do you think contribute to an environment's carrying capacity???

Resources that are limited because the rate at which

they become depleted depends on the density of the

population that uses them.

Food WaterShelter

LOGISTIC GROWTH MODEL

Once again, exponential growth is a steady increase in the population size.

Now we must consider the carrying capacity (K) and density-dependent factors when modeling population growth.

logistic model- a population model in which exponential growth is limited by a density-dependent factor. This model considers carrying capacity.

LOGISTIC MODEL

Factors that do not depend on the size of the population, but can affect it nonetheless.

Weather

Climate

Remember...

(r)= rate of growth, birthrate – death rate

(K)= carrying capacity, the population size an environment can sustain

There are 2 types of populations, (r)-strategists and (K)-strategists

r-strategist: Species that grow exponentially when the environment allows for it. Results in temporarily large populations.

When the environmental conditions are no longer suitable for the species, the population size quickly decreases.

K- strategists- organisms that grow slowly. Population sizes are usually small and kept near the carrying capacity of their environment.

K-strategists are characterized by a long life span, a slow maturing process, and reproduction late in life.