Population Ecology

What is a population? All the members of a species living in the same place at the same time. Organisms usually breed with members of their own population.

How to describe populations Density: number of individuals per unit area, or volume. Ex. Number of deer/km 2. Dispersion: The distribution or arrangement of individuals in space. Dispersion may be clumped, even or random.

Growth Rate A change in the size of a population over a given period of time = growth rate. Growth rate = births – deaths Populations usually stay about the same size from year to year as factors kill many individuals before they can reproduce.

How fast can a population grow? Reproductive potential: The maximum number of offspring that each member of a population can produce. Some species have much higher reproductive potential than others.

How many bunnies? Rabbits can begin reproducing at months Gestation is 31 days Litters can be up to 14 Females can become pregnant within hours of giving birth Lifespan is about 7 years 95 billion rabbits in 7 years!

Exponential growth Occurs only when there is enough: Food Space Little or no competition No predators Populations rarely grow at their reproductive potential

Carrying Capacity Carrying capacity is: the maximum population that an ecosystem can support indefinitely. Ecosystems change so carrying capacity is difficult to predict or calculate precisely.

Resource Limits A species reaches its carrying capacity when it consumes a natural resource at the same rate at which the ecosystem produces the resource. This resource is called the limiting resource. Examples include: light, nutrients, water.

Density Dependent Population Regulation Deaths occur more quickly in a crowded population. Limited resources, predation and disease result in higher death rates in dense populations. Ex. Emerald Ash Borer possibly going to invade Iowa

Density independent A certain proportion of a population dies regardless of population density. Ex. Severe weather