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

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