Populations in Ecology

Lesson # 27

ECOLOGY

It is the study of the interaction that living things have with each other and with their environment

Importance of Ecology

It provides the information base that society can use to make decisions about the environment

E C O L O G Y

All the members of a single species that live together in a specific geographic region.

The population of all species living in a single region.

It is the community plus all the non-living elements that interact with it (rainfall, chemicals nutrients, soil).

1- Population

2- Community

3- Ecosystem

4- The BiosphereIt is the interactive collections of all the Earth’s ecosystems.

For Ecology, life is organized into:

Arithmetic growth

4,000

13,000

25,000

7,000

16,00019,000

22,000

10,000

1,000

13 197 251 4 10 16 22

Populations: Size and Dynamics

Water flea Daphnia

Exponential growth32,000

64,000

128,000

16,0008,000

13 197 251 4 10 16 22

256,000

Populations growth exponentially because each living thing is capable of playing part in giving rise to more units.

Logistic growth: Population starts growing exponentially, but eventually the rate of growth slows and finally ceases altogether, stabilizing at a certain level (K).

Environmental Resistance

Charles Darwin: “There is not exception to the rule that every organic being naturally increase at so high a rate, that, if not destroyed, the Earth would soon be covered by the progeny of a single pair”.

Factors that limit population growth

2- Food supply

3- Living space

4- Diseases

5- Predators

6- Wastes produced by the organisms

1- Water supply

Environmental Resistance

All the forces of the environment that act to limit population growth.

Carrying capacity (K)

Environmental Resistance

It is the maximum population density of a given species that a defined geographical area can sustain over time.

When species stabilize their rate of growth to a certain level they are known as “equilibrium species”

The growth of the population of equilibrium

species is limited by carrying capacity (K)

In contrast to equilibrium species, other species like houseflies tends to fluctuate greatly in reactions to variations in its environment

Favorable weatherAbundant food supply

Fly population increases enormously

Change in temperatureFood is gone

Fly population decreases enormously

When population size tends to fluctuate greatly in reactions to variations in its environment they are

known as “opportunistic species”

The population sizes of these species tend to be only limited by their reproductive rate ( r ).r-selected species: Species whose population sizes tend to be limited by reproductive rate.

Limited by carrying capacity (K) Limited by reproductive rate ( r )Density dependent Density independentRelatively stable Relatively unstable

POPULATION SIZE

ORGANISMS

Larger, long-lived Smaller, short-livedProduce fewer offspring Produce many offspringProvide greater care for offspring Provide no care for offspring