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Population Ecology

Populations are described by density, spatial distribution, and growth rate. Population Ecology. Population Characteristics. Populations are groups of the same species in the same area. Characteristics of population include: Density Spatial Distribution Growth rate. Population density

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Population Ecology

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  1. Populations are described by density, spatial distribution, and growth rate. Population Ecology

  2. Population Characteristics • Populations are groups of the same species in the same area. • Characteristics of population include: • Density • Spatial Distribution • Growth rate

  3. Population density • The number of organisms per unit area is population density.

  4. Spatial distribution • Dispersion is the pattern of spacing of individuals of a population within an area. • Three kinds: clumped, uniform, and random

  5. Population-Limiting Factors • Limiting factors are biotic or abiotic forces that keep population from increasing indefinitely. • Limiting factors are either density-independent or density-dependent.

  6. Density-independent factors • Any factor in the environment that does not depend on the number of members in a population per unit area is a density-independent factor. • Usually abiotic, and include: • Weather events • Fire • Human alteration of the landscape • Air, land, and water pollution

  7. Density-dependent factors • Any factor in the environment that depends on the number of members in a population per unit area is a density-dependent factor. • Often biotic, and include: • Predation • Competition • Disease • Parasites

  8. Population growth rate • The population growth rate (PGR) describes how fast a given population grows. • Natality: birthrate of a population in a given year. • Mortality: death rate of a population in a given year • Emigration: number of individuals moving away from the population • Immigration: number of individuals moving into a population

  9. Births Deaths Deaths and emigrationremove individualsfrom a population. Births and immigrationadd individuals toa population. Immigration Emigration

  10. Exponential growth model • Occurs when growth rate is proportional to population size. • All populations grow exponentially until they encounter a limiting factor.

  11. Logistic growth model: • Occurs when a population’s growth slows or stops following exponential growth. • A population stops increasing when the number of births < number of deaths, or when emigration > immigration.

  12. Carrying capacity • Carrying capacity is the maximum number of individuals of a species (pop size) that an environment can support.

  13. Reproductive patterns • Species vary in the number of births per reproduction cycle, age that reproduction begins, and in the life span. • Plants and animals are placed into groups based on these patterns.

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