Population Dynamics: How Populations Change

Biotic Potential and Environmental Resistance Biotic potential – maximum reproductive rate of a population under ideal conditions –Assumes all young live long enough to reproduce –Populations must have all the resources they need to survive –Factors influencing biotic potential include, but are not limited to, the age at which an individual is able to reproduce and the number of young born at any one time

Examples of biotic potential –If a pair of houseflies produce one generation every two weeks, they could have 391,000,000 descendents at the end of one year. –Some bacteria reproduce about every 20 minutes. At this rate, 72 generations could be produced in 24 hours. The number of individuals produced would be enough to cover the entire surface of the earth to a depth of over 20 centimeters!

Biotic Potential and Environmental Resistance Environmental resistance – name given to a collection of factors that reduce the growth rate of a population –The advantage of a high biotic potential, such as the housefly, is to counteract the effects of environmental resistance.

Density Dependent Factors Definition: Factors that influence a population differently if the population is crowded than if it is not crowded. –A disease spreads more rapidly through a crowded population that through a sparse one. –A loss of a food source affects a crowded population severely since there is less food to go around..

Density Independent Factors Definition: Factors that influence all populations regardless of their density. –Forest fires –Drought –Lack of sunshine

Carrying Capacity Definition: The number of individuals a population in a particular are can support in terms of space, food, and shelter. –Interactions between biotic potential (max. reprod. rate) and environmental resistance (reduces growth rate) tend to hold most populations at a fairly stable level that matches the carrying capacity of the area. –How do humans affect the carrying capacity of an area? Remove habitats for housing Destroy the food in an area Change the flow of water in an area