• Chapter 53 – Population Ecology

Population EcologyPopulation Ecology

• The study of populations in relation to the environment, including environmental influences on population density and distribution, age structure, and variations in population size– Population – a group of individuals of a

single species living in the same general area

DensityDensity

• Number of individuals per unit area or volume

• Affected by immigration, emigration, natality, and mortality

• Measure by mark-recapture methods

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• Describe the three population dispersion patterns shown above. – What would lead to patterns like this in nature?

A B C

DispersionDispersion• The pattern of spacing

among individuals within the boundaries of the population

• Clumped – aggregated in patches

• Uniform – evenly spaced

• Random – patternless

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• Compare and contrast these 3 survivorship curves. – What reproductive strategies do you think are being used

by the organisms represented in each?

A B C

DemographyDemography• The study of the vital statistics of populations and how they

change over time (particularly birth and death rates).• Survivorship curve – a plot of the numbers in a cohort

(group of same age) still alive at each age• 3 basic types of curves: I, II, and III, but there are variations to

each (ex. crabs)

Population Life History “Strategies”Population Life History “Strategies”

r-selected (opportunistic)• Density independent

– Birth rate/death rate does NOT change with population density

• Maximizes r (rate of increase)• Short maturation and life span• Many small offspring• Usually only 1 or 2

reproductions early in life• No parental care• High death rate

k-selected (equilibrial)• Density dependent

– Death rate rises with population density

• Maximizes population size• Long maturation and life span• Few large offspring• Usually several reproductions

later in life• Extensive parental care• Low death rate

Population Growth ModelsPopulation Growth Models• Change in population size:

dN/dt = rN– N = population size– t = time – r = per capita birth rate (b) – per

capita death rate (m)

• Exponential model – idealized, unlimited environment: dN/dt = rmaxN

• Logistic growth model – includes carrying capacity (K), the maximum population size that a particular environment can support: dN/dt = rmaxN((K-N)/K)

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• Analyze the graph below and describe the relationship between the snowshoe hare population and the lynx.– How can this be explained?

Limiting FactorsLimiting Factors• Density independent factors – weather,

climate, disturbances• Density dependent factors – competition,

predation, stress, habitat, territoriality, crowding, health, disease, and waste accumulation