POPULATION ECOLOGY

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POPULATION ECOLOGY how and why populations
change in size and location over time
Population a group of individuals of the same
species living in the same place.
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Buffalo herd, Teddy Roosevelt National Park,
North Dakota (Will-Wolf)
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Aggregation Patterns in Carrion Flies
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A population of Daphnia The yellow band along
the shore in Lake Mendota, WI, indicates a a
swarm, or aggregation of millions of Daphnia per
square meter.
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Aggregated Plants Common Groundsel, Bluegrass
Individuals per unit area.
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Mytilus edulis, three species of barnacles,
quadrats, and cages.
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POPULATION ECOLOGY how and why populations
change in size location over time
Dynamics change in numbers over time
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The number by time graph.
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Exponential and Logistic models Easy to
calculate Generality Realism Precision Average
vs. Individual-Based models.
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Exponential Growth Model dN/dt rN dN/dt
1/N r A simple rule r the per capita
instantaneous growth rate rmax
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Y mX b
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Negative Exponential Growth r can be
positive zero negative
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SIMPLE MODEL CONSTANT r COMPLEX
Model Variable r
r ln (Nt/N0)/t r b d
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Human Population
dN/dt r N NT N0 erT
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DOUBLING TIME NT N0 erT The time when Nt
twice N0 Tdouble ln(2) / r Rule of Thumb r
approximately annual change (as a decimal
fraction)
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Number of individual willow plants at Newborough
Warren, Wales, after rabbits died from
myxomatosis Threshold?
N.B. Conover Munch 2002
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Maximum sustainable yield for what Population
Size is population Growth Rate highest? dN/dt
(K-N)/K(rmax)N Ludwig, 1993
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POPULATION REGULATION Density-Independence
Density-Dependence (per capita population growth
rate is a function of population size) Simple
Exponential Density Independent Logistic
Density Dependent
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Regulation by Resources Competition A struggle
for a limited resource. An interaction in which
both species suffer. K Competitive Exclusion.
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Competition The model A modified
logistic dN1/dt (K-N1- (a2,1N2))/K
rmaxN1 Density Dependent or Independent?
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Two kinds of Competition Scramble
(exploitation) Interference The logistic model
works best for EXPLOITATION competiton.
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Fundamental Question Why are there so many
species? Competitive Exclusion ( Logistic
model) VS. Non-Equilibrium Dynamics Predation
(Keystone) Temporal Refuge (Seed Bank) Spatial
Refuge (Metapopulation)
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Figure 52.20 Population cycles in snowshoe hare
and lynx
Hutchinson and Elton were fascinated by
population cycles
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Regulation by Predation PREDATION MODEL
dY/dt (b1)Y (d1X)Y dX/dt (b2Y)X
(d2)X Density Dependent?
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Parasites Infection Small Predators INFECTION
The action or process of affecting injuriously,
or the fact of being so affected corrupted or
diseased condition. OED
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Parasitism and Fitness
2 Grackle species
Parasites Disease Mutualism McMichael, Zimmer
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