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Population Ecology ECOLOGISTS STUDY ENVIRONMENTS AT DIFFERENT LEVELS OF ORGANIZATION. Organism Population Community Ecosystem Biome Population Ecology Population: all the organisms that both belong to the same group or species and live in the same geographical area Specific species at the same place at the same time Example: 1,738 trout in Kentucky Lake in 1986 Population Size The size of a population is always changing! Four factors affect the size of a population: Immigration (coming in) Births Emigration (leaving) Deaths Population Density Population Density: The number of individuals that live in a defined area Helps scientists determine how crowded an area is Formula: # of individuals= population density Area (units2) Population Growth Population growth is based on available resources. WATER FOOD SHELTER Population Growth Exponential Growth (J curve) Rapid population increase due to an abundance of resources. Population Growth Logistic Growth (s curve) Due to a population facing limited resources No more will fit!!! Population Growth Carrying Capacity The maximum number of individuals that the environment can support When resources run out the population cannot keep growing Population Growth Ecological Factors limit population growth. Limiting Factors: Something that keeps the size of a population down Limiting Factors Density-dependent limiting factors: Depend on the number of individuals in a given area. Examples: Predation Competition (competing for resources) Parasitism & disease Have a larger effect in densely populated areas Limiting Factors Density-independent limiting factors: Limit a population’s growth regardless of the number of individuals Examples: Unusual weather Natural disasters Human activities