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Behavior  Population Dynamics

Behavior  Population Dynamics. Behavior Directly Governs Individual Demographic Performance Indirectly Effects Population Dynamics Population Growth Implies Chance of Extinction Here, Take Behavior = Social Organization. Extinction. Population extinction process

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Behavior  Population Dynamics

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  1. Behavior  Population Dynamics Behavior Directly Governs Individual Demographic Performance Indirectly Effects Population Dynamics Population Growth Implies Chance of Extinction Here, Take Behavior = Social Organization

  2. Extinction Population extinction process Four general causes of extinction 1. Environmental stochasticity 2. Demographic stochasticity 3. Abiotic catastrophes 4. Lack genetic variation

  3. Extinction Environmental stochasticity Random, temporal variation: exogenous factor (s) Individuals’ experience same birth, death rates Temporal fluctuations, Between-generation scale Good, Bad Years = Generations: food abundance Small population & bad year  Extinction

  4. Extinction Demographic stochasticity Random variation among individuals, Within-generation scale Number offspring, survival Individuals’ birth and death rates independent, hence can differ Important small populations: chance extinction

  5. Extinction Demographic stochasticity Fix time; Extinction Pr declines with Initial population ize Fix Pop size; Extinction Pr increases with time MTE = (Extinction Pr)-1

  6. Extinction Abiotic (Physical) Catastrophes Large, sudden density reduction Environmental, anthropogenic Climate change Time scale relative to generation time

  7. Extinction Genetic Lack variation, population fails to adapt Rarest, but [again] global climate change

  8. Behavior  Population Dynamics Vucetich et al. 1997. Effects of social structure and prey dynamics on extinction risk in gray wolves. Conservation Biology 11:957. 1. Wolves: social behavior - group, pack 1 litter/year, dominant female amplify demographic stochasticity 2. Prey availability: fluctuate, source of environmental stochasticity

  9. Behavior  Population Dynamics Gray wolf (Canis lupus) Isle Royale, MI; island in Lake Superior National Park, > 500 mi2 Wolves feed on moose Abundance of old moose (> 9 yrs) key

  10. Behavior  Population Dynamics Objective: Simulate wolf population dynamics Predict mean time to extinction (MTE) 1. Age-dependent mortality in wolves 1/3 pups die first year No wolves older than 11 yrs 2. Random litter size in wolves, Mean = 1

  11. Behavior  Population Dynamics 3. Wolf packs: Some restructuring between years When prey abundance falls, smallest pack disperses, mortality cost Survivors join another pack Number packs proportional to no. old-moose

  12. Wolf/Pack Count vs Moose

  13. Wolf, Pack, Moose Dynamics

  14. Behavior  Population Dynamics Mean Time to Extinction, Wolf Population Weak dependence, initial population size Standard result not observed Strong effect, initial number of packs

  15. Simulation results

  16. Behavior  Population Dynamics Reproductive unit is pack Number packs, not population size critical extinction process Social organization, with dominance-based breeding, amplifies effects of demographic stochasticity on extinction

  17. Behavior  Population Dynamics No. old moose constant = 305 Wolves: MTE = 155 yrs No. old moose cycles, mean = 305 Wolves: MTE = 105 yrs Environmental stochasticity Standard result

  18. Behavior  Population Dynamics Social group size Individual demographic performance How might group size G influence population dynamics? Trainor, K.E. & T. Caraco. 2006. Group size, energy budgets and population dynamic complexity. Evolutionary Ecology Research 8:1173-1192.

  19. Model Assumptions (1) • Foragers search in groups, G individuals • Rate food-clump discovery •  1/(population density) Density dependence •  G; interference, mutualism • Energy consumption random • Number clumps, clump size

  20. Model Assumptions (2) • Starvation • Consumption  energy requirement • Variation between groups • Predation while foraging • Random independent attacks • Increases with consumer density

  21. Survival & Reproduction • Surviving non-breeding season • Avert starvation • Avoid predation • Reproduction: R fixed • Survivor + (R-1) offspring

  22. Return Map (1) • nt+1 = F(nt) nt • F(nt): Density-dependent reproduction • F = R x p(avert starvation |G,n) x p(avoid predation |n)

  23. Stable dynamics: stable node • For α > 1, Q = 8, Vc = 1.0; G = 28 nt t

  24. Stable dynamics: stable node • α > 1 (mutualism ?) Individual encounters clumps faster as G increases Mean energy intake may Increase Energy intake variance declines

  25. Stable Cycle • For α = 1.0, Q = 10, Vc = 0.5; G = 32

  26. Stable Cycle • α = 1.0 Individual encounters clumps independently of G Mean energy intake independent of G Energy intake variance declines

  27. Complex dynamics • For α = 0.8, Q = 12, Vc = 0.5; G = 20

  28. Complex dynamics • α < 1 (interference) • Individual encounters clumps slower as G increases Mean energy intake declines with G Chaotic dynamics; often near extinction

  29. Behavior  Population Dynamics Interactions among individual group members Interference, independence, mutualism Survival through non-breeding season Complexity of population dynamics Likelihood of extinction

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