Population properties

What is a population?

Distribution and Range• distribution• geographic range – total extent (red maple)

– to N, -40 degrees C limit it– to W, dry conditions limit it– to S, ocean and wetlands limit it

• Distribution patterns different at different scales

• Moss (Tetraphis sp.)

• Microhabitat :

– temperature– humidity– pH– stream banks with

conifer stumps in one area provide these

• Abundance = total number of individuals in a population, no. red dots

• Density = number of individuals per unit area

• Spatial distributions, and causes

Uniform, desert shrubs; Clumped, caterpillars

patterns may indicate important ecological processes

how and why hypotheses generated

Estimating population size.

• Population size (number of individuals)

• 2 components:– density, the number of individuals per unit area– area occupied

• Density area occupied = population size.

Measuring density

• A total count may be possible:

– if individuals can be distinctively marked– larger endangered species

• For sessile organisms, local density may be determined in plots, then extrapolated to entire area occupied.

Mark-Recapture Method• Mark-recapture - used with animal populations:

– initial sample, mark individuals – Release marked animals, allowed to mix– second sample, tally marked and unmarked ones

Computations

• M = initial marked sample• n = size of second sample• x = number of marked animals in second sample

• What is N (population size):N (Est. popln. size) = nM/x

• M = 20 fish are captured, marked, and returned• n = 50 (x = 5 marked fish)• .

Populations have age structure

Aging organisms

Most species have a dispersal stage

• Sponges planula larvae• Corals, jellyfish ciliated larvae• parasitic flatworms ciliated larvae• clams veligers• barnacles small larvae• plants wind-dispersed seeds• plants animal dispersed fruits

• Passive versus active/directed dispersal

Why disperse?• Reduce competition from parents, siblings

• Find more food, other needed resources

• Locate needed microclimate

– emigration – moving out of a subpopulation– immigration – moving into a subpopulation– these movements affect population sizes and gene

flows – (gene flow homogenizes gene pools)

• Risks of dispersal

– unknowns of new area, increased predation

Migration– a round-trip– May be local or global– Zooplankton, through a water column– Some invertebrates, mammals and birds migrate

– Zooplankton daily migrate in water column, light– Earthworms overwinter deep in soil to avoid frost– Caribou migrate to arctic tundra winter, lichens– Waterfowl and shorebirds

• migrate to rich northern breeding grounds, food

– Conservation issues and migration• one species may need habitats in 3 different countries!

Distributions and density change over space and time – e.g., European

gypsy moth