POPULATION ECOLOGY

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 CURVE-TRACKS

• TYPE I– Low death

rates early in life

• TYPE II– Death rate

constant • TYPE III

– High death rates early on in life

• Which curve would fit an organism that cares for its young and reproduces relatively late in life?

• Which curve would be typical of an organism that experiences high predation as small individuals but when they are adults are more able to avoid most predators?

• Which curve might best fit rodents that die in numbers at all ages?

POPULATION GROWTH• EXPONENTIAL ( r )

• Very rapid• Rate of growth

constantly increases• Assumes unlimited

resources are available

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

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

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)

SELF-ASSESSMENT• Directions: ANSWER the questions and then justify WHY that is the CORRECT

answer.1. The observation that members of a population are uniformly distributed suggests that

a) The size of the area occupied by the population is increasing.b) Resources are distributed unevenly.c) The members of the population are competing for access to a resource.d) The members of the population are neither attracted to nor repelled by one another.e) The density of the population is low.

2. Population ecologists follow the fate of same-age cohorts to a) Determine a population’s carrying capacity.b) Determine if a population is regulated by density-dependent processesc) Determine the birth & death rate of each group in a populationd) Determine the actors that regulate the size of a populatione) Determine if a population’s growth is cyclic.

3. Which of the following statements about human population in industrialized countries is INCORRECT?

a) Average family size is relatively small.b) The population has undergone the demographic transition.c) Life history is r-selected.d) The survivorship curve is Type I.e) Age distribution is relatively uniform.