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