Ecology POPULATIONS

Objectives Identify factors that limit population size. Differentiate between density-dependent and density-independent factors.

The following standards will be addressed:

KEY CONCEPT Populations grow in predictable patterns.

Changes in a population’s size are determined by immigration, births, emigration, and deaths. The size of a population is always changing. Four factors affect the size of a population. immigration births emigration deaths

Population Growth Natural populations vary in size from year to year. Three factors affect population size: Number of births The birth rate. Number of deaths The death rate. Number of individuals entering/leaving Immigration: movement into a population Emigration: movement out of a population

Birth Rate > Death Rate: Population Grows Population Growth Birth Rate > Death Rate: Population Grows Birth Rate < Death Rate: Population Declines Birth Rate = Death Rate: Population Steady

Population growth is based on available resources. Exponential growth is a rapid population increase due to an abundance of resources.

Exponential Growth If a population has abundant space and food, and is protected from predators and diseases, then the population will multiply and the size will increase. Populations will exhibit exponential growth. Shown via an exponential model.

Logistic Growth The Earth is NOT covered by unlimited organisms-Why? There are not abundant resources. When a population’s growth stops or slows following a period of exponential growth, it is now considered logistic growth (logistic model).

Carrying capacity is the maximum number of individuals in a population that the environment can support. A population crash is a dramatic decline in the size of a population over a short period of time.

Ecological factors limit population growth. A limiting factor is something that keeps the size of a population down. There are two types: density-dependent density-independent

Density-dependent limiting factors are affected by the number of individuals in a given area. predation competition parasitism and disease

Density-independent limiting factors limit a population’s growth regardless of the density. unusual weather natural disasters human activities