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Population Ecology

Population Ecology. Characteristics of Populations Life History Traits Population Growth Models Regulation of Population Growth. Density-number/unit of area or volume Census Estimate by indirect indicators Mark-recapture method. Dispersal-spacing among individuals Clumped-humans

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Population Ecology

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  1. Population Ecology Characteristics of Populations Life History Traits Population Growth Models Regulation of Population Growth

  2. Density-number/unit of area or volume Census Estimate by indirect indicators Mark-recapture method Dispersal-spacing among individuals Clumped-humans Uniform-penguin rookery Random-not common in nature Characteristics of Populations

  3. Demography • Study of vital statistics • Age structure • Birth rate (fecundity) and death rate • Generation time • Sex ratio • Survivorship curves

  4. Survivorship Curves • Type I-little change during early and middle life (humans and large mammals) • Type II-constant mortality over the life span, (squirrels) • Type III-very high mortality for the young, but few after a certain age (oysters)

  5. Life History • An organism’s schedule of reproduction and death • Includes: 1. Number of reproductive episodes/lifetime 2. Number of offspring/reproductive episode 3. Age at first reproduction

  6. Population Growth Models • Exponential growth-describes an idealized population in an unlimited environment • Logistic model-incorporates the concept of carrying capacity; assumes rate of growth slows as it approaches the carrying capacity (K) • Two types of populations: K-selected (few offspring), r-selected (high reproductive rate)

  7. K-Selection • Common in populations that live at densities close to the carrying capacity (K) of their environment • Maturity and reproduction at a later age • Production fo few, well-cared for young

  8. r-selection • Populations that maximize (r), the intrinsic rate of increase • Individuals mature early, produce large numbers of offspring at a time • Maximize reproductive success in uncrowded, unpredictable environments • Many insect and weed populations

  9. Population Limiting Factors • Density-independent factors-unrelated to population size and affect the same percentage of individuals regardless of the size of the population (weather) • Density-dependent factors-intensifies as population size increases (resource limitation)

  10. Boom or Bust Cycles • Show a regular fluctuation in density • Insects, small mammals (lemmings, snowshoe hares) • May result from a time lag in the response to density-dependent factors

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