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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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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

Four general causes of extinction

1. Environmental stochasticity

2. Demographic stochasticity

3. Abiotic catastrophes

4. Lack genetic variation


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


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


Extinction

Demographic stochasticity

Fix time; Extinction Pr

declines with Initial

population ize

Fix Pop size; Extinction Pr

increases with time

MTE = (Extinction Pr)-1


Extinction

Abiotic (Physical) Catastrophes

Large, sudden density reduction

Environmental, anthropogenic

Climate change

Time scale relative to generation time


Extinction

Genetic

Lack variation, population fails to adapt

Rarest, but [again] global climate change


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


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


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


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


Wolf/Pack Count vs Moose


Wolf, Pack, Moose Dynamics


Behavior  Population Dynamics

Mean Time to Extinction, Wolf Population

Weak dependence, initial population size

Standard result not observed

Strong effect, initial number of packs


Simulation results


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


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


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.


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


Model Assumptions (2)

  • Starvation

    • Consumption  energy requirement

    • Variation between groups

  • Predation while foraging

    • Random independent attacks

    • Increases with consumer density


Survival & Reproduction

  • Surviving non-breeding season

    • Avert starvation

    • Avoid predation

  • Reproduction: R fixed

    • Survivor + (R-1) offspring


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)


Stable dynamics: stable node

  • For α > 1, Q = 8, Vc = 1.0; G = 28

nt

t


Stable dynamics: stable node

  • α > 1 (mutualism ?)

    Individual encounters clumps faster as G increases

    Mean energy intake may Increase

    Energy intake variance declines


Stable Cycle

  • For α = 1.0, Q = 10, Vc = 0.5; G = 32


Stable Cycle

  • α = 1.0

    Individual encounters clumps independently of G

    Mean energy intake independent of G

    Energy intake variance declines


Complex dynamics

  • For α = 0.8, Q = 12, Vc = 0.5; G = 20


Complex dynamics

  • α < 1 (interference)

  • Individual encounters clumps slower as G increases

    Mean energy intake declines with G

    Chaotic dynamics; often near extinction


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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