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

Characteristics of Populations 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

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

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)

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

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)

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

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

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)

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