Population Dynamics Ecology Chapter 4.1

Principles of Population Growth A population is a group of organisms of the same species that live in a specific area. A population is a group of organisms of the same species that live in a specific area. Healthy populations will grow and die at a relatively steady rate unless resources run out or disease. Healthy populations will grow and die at a relatively steady rate unless resources run out or disease.

Population Growth Populations grow on a J-curve or exponential curve. Populations grow on a J-curve or exponential curve. Rates start slow and then rapidly increase. Rates start slow and then rapidly increase.

Limits on Growth Can populations grow forever? NO. Can populations grow forever? NO. Populations reach limiting factors like food, disease, predators, lack of space. Populations reach limiting factors like food, disease, predators, lack of space. This is depicted in a graph of population #’s as a S-curve. This is depicted in a graph of population #’s as a S-curve.

Carrying Capacity The number of organisms of one species that an environment can support indefinitely is its carrying capacity. The number of organisms of one species that an environment can support indefinitely is its carrying capacity. What is human’s carrying capacity? What is human’s carrying capacity?

Reproduction Patterns In nature, animals and plant populations change in size- even at different times of the year. In nature, animals and plant populations change in size- even at different times of the year. Reproductive patterns are known as life- history patterns. Reproductive patterns are known as life- history patterns. There are two patterns- slow (humans) and rapid (mosquitoes). There are two patterns- slow (humans) and rapid (mosquitoes).

Slow and Fast life-history Rapid- usually small organisms in unpredictable environments that rapidly mature and have a short life. Rapid- usually small organisms in unpredictable environments that rapidly mature and have a short life. Slow- live in stable environments and have a long life span and mature slowly. They usually live around the carrying capacity. Slow- live in stable environments and have a long life span and mature slowly. They usually live around the carrying capacity.

Density factors Density-dependent factors- factors that have an increasing effect on a large, growing population. Diseases, predators, food, parasites. Density-dependent factors- factors that have an increasing effect on a large, growing population. Diseases, predators, food, parasites. Density-independent factors- factors that affect populations regardless of size or density. Abiotic factors like fires, floods, drought… Density-independent factors- factors that affect populations regardless of size or density. Abiotic factors like fires, floods, drought… Populations are either randomly spread, clumped, or uniform. Populations are either randomly spread, clumped, or uniform.

Dependent or Independent?

Uniform/Random/Clumped

Predation and Population Size Populations of predators and their prey experience cycles or changes in their numbers over periods of time. Populations of predators and their prey experience cycles or changes in their numbers over periods of time.

Crowding and Stress When populations are crowded, organisms exhibit symptoms of stress. When populations are crowded, organisms exhibit symptoms of stress. Populations exhibit aggression, decrease in parental care and decreased resistance to disease. Populations exhibit aggression, decrease in parental care and decreased resistance to disease.