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Population properties What is a population?

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

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Population properties What is a population?

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  1. Population properties What is a population?

  2. 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

  3. Distribution patterns different at different scales • Moss (Tetraphissp.) • Microhabitat : • temperature • humidity • pH • stream banks with conifer stumps in one area provide these

  4. Abundance = total number of individuals in a population, no. red dots • Density = number of individuals per unit area • Spatial distributions, and causes

  5. Uniform, desert shrubs; Clumped, caterpillars patterns may indicate important ecological processes how and why hypotheses generated

  6. Estimating population size. • Population size (number of individuals) • 2 components: • density, the number of individuals per unit area • areaoccupied • Density  area occupied = population size.

  7. 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.

  8. 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

  9. 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) • .

  10. Populations have age structure

  11. Aging organisms

  12. 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

  13. 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

  14. 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!

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

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