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
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