Population Ecology

Why Study Populations?

A population is a group of organisms of the same species that live in a given area.

Populations are the smallest unit that can exhibit evolution.

Populations are the foundations of the earth’s ecosystems.

Population Growth

The environment has a direct impact on how populations grow and develop.

Population growth can be measured in one of two ways. Exponential growth and Logistic growth.

Exponential Growth

Represents the ideal conditions available for an organisms growth.

Rapid increase in the population.

The larger the population gets the faster it grows.

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Number of Generations

Logistic Growth

A type of population growth that deals with environmental factors limiting it development.

Contains 5 stages. Initial Growth Exponential Growth Slow Growth Slower Growth Steady State

Factors that Control Population Growth

Density Dependent FactorsDensity Independent Factors

Density- Dependent Factors

When factors that control population size have more of an effect on larger populations than smaller ones.

Examples: competition, predation, parasitism, and crowding.

Competition

When populations are crowded they compete for the necessities of life.

Competition between members of similar but different species fuels evolutionary change.

Example: Two different species of herbivores (cows and kangaroos) competing for the same stand of plants.

Predation

Almost every species serves as a food supply for other species.

Predators kill and eat organisms, while the prey are eaten.

Prey and predators evolved together over a long period of time.

This type of relationship keeps an ecosystem in balance.

Prey Predator Model

Prey Predator Relationship

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Rabbits Foxes

Parasitism

Parasites live off their host.They work better in crowded conditions.Few parasites kill their host.

Crowding and Stress

Most animals need a certain amount of space to function properly.

Organisms will fight each other for space if they are over crowded.

Stress causes changes in the normal hormonal balances in organisms.

Large amounts of adrenaline given off during stress may cause more fighting and less breeding, lowering of the immune system, altered female behavior.

Density- Independent Factors

These factors are not related to population size.

Most of them are natural occurrences.Forest fires, hurricanes, volcanic

eruptions, cold or hot weather, and drought.

Symbiosis

Relationships between organisms.Commensalisms: One organism is

benefited and the other is not harmed.Mutualism: Both organisms benefit from

the relationship.Parasitism: One benefits and the other is

harmed.