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Chapter 52

Chapter 52. Population Ecology. Population density. Density = # of ind per unit area or volume 3 ways to measure Aerial count of herds, tall trees in savanna Random (sample) plots to count individuals or nests, burrows, tracks Mark-recapture Capture, mark, release, recapture

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Chapter 52

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  1. Chapter 52 PopulationEcology

  2. Population density • Density = # of ind per unit area or volume • 3 ways to measure • Aerial count of herds, tall trees in savanna • Random (sample) plots to count individuals or nests, burrows, tracks • Mark-recapture • Capture, mark, release, recapture • Pop size = total recaptured X (marked & released) marked & recaptured

  3. Patterns of population dispersion – p. 1138 • Clumped – individuals in patches • Most common • Uniform – territoriality • Random • Ex – wind blown seeds

  4. Factors affecting population size • Age at 1st reproduction • # of offspring/year – natality (birth rate) • Life expectancy – death rate • Movement of organisms • Immigration • emigration

  5. Survivor ship Curve Type I – human – greatest survival to old age Type II – squirrel – medium survival Type III – clam – greatest deaths early

  6. Life History Strategies • Opportunistic species (r-selection) • Density-independent • Population densities tend to fluctuate below carrying capacity or have little competition so overshoot & crash • Many offspring quickly • No parental care • Short lifespan • Small offspring • Weeds, salmon, insects, starfish, mice

  7. Equilibrium species (k-selection) • Density dependent • Few young • Parental care • Reproduce at more mature age • Long lifespan • Large offspring • Birds, whales, elephants, humans, hardwood trees

  8. Population Growth Models • Exponential model – typical of populations introduced to a new area or whose # have been reduced • Ex – single pair of elephants produce 19 million in 750 years • Single bacterium divides every 20 mins, can cover the earth 1 ft deep in 36 hours • Begin with a few individuals and unlimited resources, but can lead to crash as resources become limited

  9. Logistic Model • The per capita rate of growth is reduced as the population nears the carrying capacity • Carrying capacity – maximum population size that can be maintained in a particular area

  10. Carrying capacity • # of population that can be maintained indefinitely in the ecosystem • dN = rN(K-N) dt K If population (N) is small, equation works as if it were just rN As N increases, growth slows b/c it is being multiplied by a fraction If N=K, growth is zero

  11. Limiting Factors • Density dependent LFs – only come into play or intensify when the population becomes denser • Food • Disease • Sunlight for plants • Hormonal changes • Space, nesting sites • predation

  12. Density-independent LFs – affect both large & small populations the same • Climate, weather • Disasters – flood, drought, fire

  13. Human Population GrowthPresent population 7.1 billion

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