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