Population Dynamics How Populations Change Biotic Potential and

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 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