Population Ecology

Populations

• interacting group of members of a species

• defined area: range

• density

• measured at a defined time

range

• most species have a limited geographical distribution

endemic

• a species limited to a defined location

cosmopolitan

• distributed widely

Random dispersion

• not interacting

• random due to variation in factors like wind

• average fitness increases

clumped dispersion

• hunting in a pod, increases nutritional status

• higher fitness: selection favors individuals that find patchy resources

uniform/regulat dispersion

• minimize interactions with neighbors (competing with each other for something)

• challenge form neighbor too close

• competition reduces fitness

population change

• individuals born and die

• immigration (in) and emigration (out)

how do you measure population change?

• count them (full census) —> ex: tagging seals

• estimate from representative samples

how do you estimate population size?

• N=(n1 x n2)/M

• (# caught 1st time x # caught second time)/ # marked

life tables

• predict future population size based on how long they live, likelihood of survival at a given age, when (and how well) reproduction occurs

how does environment affect life histories?

• how long they live and how many offspring produces are highly dependent on environment

  • food, weather, predators

survivorship curves

Type1,2,3

Type 1 survivorship curve:

• most individuals survive to reproduction

  • few offspring, long lives

  • ex: humans

Type 2 survivorship curve:

• constant risk of mortality at all ages

  • ex: birds

Type 3 survivorship curve:

• most die as juveniles

  • many offspring, low parental care

  • ex: mollusks, insects

life history strategies

• organisms partition time and energy into: growth, maintenance, reproduction

• Variable: dependent on resources, mortality

  • affects how fast populations grow: r=b-d

limits to population densities

• if resources (food habitat) are unlimited, how big can populations get?

• exponential growth

carrying capacity

• exponential growth can occur for short periods

• ends when something needed becomes limited (food, nesting sites, shelter)

• environment can provide only a limited amount of such a resource

logistic growth curve

• as size of population reached K, growth in population size slows

r strategist

• high rates of reproduction, broad range of habitats, many offspring, limited parental investment, population size fluctuates

• “prioritize producing many offspring with minimal parental care for unstable environments”

k strategist

• population steady neat K, narrow range, high parental investment, long lives

• “invest heavily in fewer offspring for stable environments, aiming for high survival rates (K for carrying capacity)”

Density dependent factors (biotic)

• food can become scarce: poor nutrition = slow birth rate and speeds up death rate

• large pop attract predators

• dense pop pass disease among members

Density independent factors (abiotic)

• natural disturbances (extreme cold, hurricanes)

• reduce pop regardless of density

metapopulation

• provides new individuals if a particular patch dies off

• requires “corridors” - physical connections among patches

  • island =none