Population Ecology II-PRS

Population Ecology II-PRS - Georgia Tech School of Biology...

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Biology 1510/1511 Georgia Tech School of Biology Fall 2008 The Logistic Growth Model Adds an expression that reduces the per capita rate of increase as N increases h h h h h h - = K N K N r dt dN max the # left till K is met When N is small large fraction of K left for population growth When N is large small fraction of K left for population growth Number of generations Population size (N)
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Biology 1510/1511 Georgia Tech School of Biology Fall 2008 Logistic growth in real populations Where is K?
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Biology 1510/1511 Georgia Tech School of Biology Fall 2008 Logistic Model Assumptions Constant carrying capacity No time lags Linear density dependence – each individual (+ or -) has the same effect on population growth
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Biology 1510/1511 Georgia Tech School of Biology Fall 2008 The Allee effect Birth rates may be low when populations are small Births / female Population size (N) Why would this be important (think conservation biology)?
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Biology 1510/1511 Georgia Tech School of Biology Fall 2008 Factors that regulate population growth Population growth decreases when “b” decreases, “d” increases or both A birth or death rate that does not change with population density is density independent Factors that kill similar proportions of individuals regardless of density (i.e. a flood may kill 90% of plants in a population no matter if there are 100 or 1000 individuals)
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Biology 1510/1511 Georgia Tech School of Biology Fall 2008 Density Dependent Population Regulation Populations can reach a stable equilibrium density through negative feedback when birth and/or death rate is density dependent
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Biology 1510/1511 Georgia Tech School of Biology Fall 2008 Competition and birth rate As resources per individual drop individuals will have a hard time obtaining sufficient resources to reproduce Soay sheep on Hirta Island
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Biology 1510/1511 Georgia Tech School of Biology Fall 2008 Density dependent factors Territoriality : Maintaining a territory will enable an individual to capture enough food to reproduce Disease : Transmission rate often depends on population density Predation : Predators may concentrate on the most abundant prey Toxic Wastes : Metabolic by-products accumulate as populations grow
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Biology 1510/1511 Georgia Tech School of Biology Fall 2008 Population cycles Some populations show periodic fluctuations on regular intervals - trapping records kept by the Hudson Bay Company Boom and bust cycles
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Biology 1510/1511 Georgia Tech School of Biology Fall 2008 Population cycles Why do the populations rise and fall in 10 year cycles?
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Biology 1510/1511 Georgia Tech School of Biology Fall 2008 Hypotheses Food shortages during the winter Predators overexploit the hares Sunspot activity - supplementing the food resources of the hares DID NOT eliminate the cycles - tracked hare mortality and found that 60% -90% were killed by predators - cycles do not match hare population cycles ( MacLulich 1937, Moran 1949)
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Biology 1510/1511 Georgia Tech School of Biology Fall 2008 A HUGE experiment C Food Fertilizer Food C Food Fence C Food Fertilizer Fence Food 1 km 1 km
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Biology 1510/1511 Georgia Tech School of Biology Fall 2008 What happened? 0
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This note was uploaded on 09/04/2009 for the course BIO 1510 taught by Professor Unknown during the Spring '07 term at Georgia Institute of Technology.

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Population Ecology II-PRS - Georgia Tech School of Biology...

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