Population Ecology

Biology 1-2

Population Ecology

Population ecology studies changes in population size and the factors control their size over time. Population-a group of individuals of the same

species in a defined area.

Population Growth

The size of a population is based on two sets of opposing factors. Growth factors-factors that cause a population to

grow. Lots of food or living space, good climate, little

competition or predation. Limiting factors-factors that cause a population to

shrink. Little food or living space, poor climate, lots of

competition/predation, disease.

Exponential Growth

If given unlimited space and resources, a population can grow exponentially. No environment can

support exponential growth forever.

Resources are limited.

Carrying Capacity

Growth and limiting factors work against each other to create an upper limit to a population. Carrying capacity-maximum number of

individuals an area can support indefinitely.

Carrying Capacity cont’d

Growth factors cause the population to increase. Limiting factors slow the

growth rate. At the carrying capacity,

the growth rate is zero.

Life Histories

The life history of an organism is all the events from birth to death. Includes: When it reproduces. How often it reproduces. Number of offspring. Amount of care.

Life Histories cont’d

Organisms can be put into two groups, based on their life histories. r-selected species K-selected species

r-Selected Species

r-selected species use most of their energy for their offspring. Produce lots of offspring. Provide little or no care for the young. Tend to be smaller and shorter lived organisms. Have low survival rates.

If they make it past infancy they live to an old age. Allows them to succeed in unstable environments.

r-Selected Species cont’d

r-selected populations reproduce rapidly and easily overshoot the carrying capacity. They grow rapidly and use up resources. Limiting factors increase and their numbers drop

off. Too many predators, not enough food.

When the population is low enough they recover. Less predation, more food.

Swing back and forth around the carrying capacity.

K-Selected Species

K-selected species are organisms that put their energy into raising their young. Have fewer offspring. Provide lots of care for the young. Higher infant survival rates. Tend to be larger and longer lived.

K-Selected Species cont’d

K-selected populations grow much more slowly. Level off as they near the carrying capacity. Reproduce so slowly they cannot handle change

very well. Work to ensure the survival of their young.