Population Ecology

Chapter 4.1 Population Dynamics

Objectives

Describe characteristics of populations.

Understand the concepts of carrying capacity and limiting factors.

Describe the ways in which populations are distributed.

What are some observations you can make about populations of insects over the course of a year?

More mosquitoes and flies in the spring and summer.

More spiders in the fall.

Less visible insects in the winter. Does this mean all the insects die

over the winter? No, some just find places to live

and others migrate to warmer areas.

Characteristics used to classify all populations of organisms

All species occur in groups. We call these groups populations.

The characteristics used to classify all populations are: Population Density: Dispersion Populations Ranges

Population Density

What does the term “dense” mean?

Dense means how many things are in an area. The more thing the more dense the population is.

Low Density

High Density

Spatial Distribution

Spatial Distribution is how organisms are distributed. Where do they live.

How do we classify how organisms are distributed?

• Dispersion, or the pattern of spacing of a population within an area.

– Uniform dispersion: usually dispersed in a neat equal pattern.

– Clumped dispersion: dispersed where herds live in large packs or clumps in areas within the area they live.

– Random dispersion: where it is unpredictable where they live.

Population Ranges

Where organisms live

No organism, including humans, live in all habitats in the biosphere.

Some species can not adapt to the abiotic conditions of the area.

For example, an alligator would not live in the Great Lakes.

Can you guess what abiotic factor the alligator could not adapt to?

Population Limiting Factors

Limiting factors are things that keep a population from continuing to increase indefinitely.

Two categories of limiting factors: Density-independent factor Density-dependent factor

Density-independent factor

• Usually are abiotic (non-living) and include natural phenomena.

– The Tsunami in Japan is an example of a abiotic density-independent factor.

– The drought in Africa is another example.

• It also includes human modification to landscapes and areas.

– The destruction of the rain forest has limited and even wiped out organisms.

Density-dependent factor

Any factor in the environment that depends on the number of members in a population per unit area.

These are often biotic (living) factors.

Examples are predation, disease parasite, and competition.

Population growth rate

How fast a given population grows.

Emigration: number of individuals moving away from an area. Not just people.

Immigration: individuals moving into a population. Again, not just people.

What would happen if nothing restricted a population from growing?

Exponential growth model: Shows how a population would grow if there were no limits placed on it by the environment.

How do populations usually grow?

Logistic growth model: most populations experience times of growth and times on maintaining population. The logistic growth model demonstrates this type of growth.

Carrying capacity

• What is the largest number of organisms a population can support?

• Carrying capacity is the largest number of organisms a population can support.

• When resources are plentiful there are more births than deaths.

• When resources are limited there are more deaths than births. If this happens the population has exceeded its carrying capacity.

Reproductive Patterns

• Not all organisms reproduce at the same rate.

• Ever hear the term “reproduce like bunnies?”– Bunnies produce more offspring than some

species. – People reproduce at a rate slower than bunnies,

but faster than elephants.

• R-Strategies are organisms that reproduce at a faster rate. Their goal is to produce as many offspring as possible in a short time period in order to take advantage of some environmental factor.

• K-Strategies are organisms that reproduce fairly predictably. Elephants reproduce at a predictable rate. Their goal is to produce fewer offspring that will live to be at an age that can reproduce themselves.