Population Dynamics

1Populations.ppt

Vocabulary

• Population• Biotic Potential• Carrying Capacity• r-Selection• K-Selection• Survivorship Curve

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Population

• number of individuals of a species in a defined place and time.

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Dynamic characteristics of populations

Dynamic characteristics of populations

• Population size, number of individuals (N)

• Density (N/ area)

• Dispersion– Random– Uniform– Clumped

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Dynamic characteristics of populations

• Age distribution,– proportions of young, middle-aged, old– Differs in growing, stable, decreasing populations

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Changes in populations

• Growth – Expansion of species’ populations may lead to

evolution of new species

• Decline– Shrinking species’ populations may lead to

extinction• Small populations

• Narrowly specialized species

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Changes in populations

• ΔN = +B +I –D –E+B = births (birth rate)

+I = immigrants (immigration rate)

– D = deaths (death rate)

– E = emigrants (emigration rate)

– (For many [most] natural populations I and E are minimal.)

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Population growth

– B > D

– Exponential growth, dN/dt = rN• N = number, pop.size

• r = biotic potential (maximum reproductive capacity of an organism if resources are unlimited)

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Population growth

• Exponential growth unlimiteddN/dt = rN

• Unrealistic

Carrying Capacity

• The population size that the environment can sustain for a long period of time.

• Determined by– Renewable resources (water, light, etc)– Nonrenewable resources (land)

Population growth

• Logistic growth, dN/dt = rN (1 - N/K)

• N = number, population size

• r = biotic potential

• K = carrying capacity

– Better represents real populations

Population growth

• Logistic growth, – dN/dt = rN (1 - N/K)

• N = number, population size

• r = biotic potential, “intrinsic rate of increase.”

• K = carrying capacity

– Better represents real populations

Logistic model

• Logistic model works, to a point.– Real organisms have time lags for growth, time to

develop eggs, flowers, etc.

– Real populations may exceed carrying capacity.• Kaibab Deer

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Various species have various strategies for coping with a

variable world.

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Two general types ofReproductive Strategies

Survivorship Curves•Plots surviving individuals at different age groups– r-strategists have Type III

– K-strategists have Type I

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Survivorship Curves

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Type I survivorship curves are characterized by high survival in early and middle life, followed a rapid decline in survivorship in later life. Humans are one species that show this pattern of survivorship.

Type II curves are an intermediate between Type I and III, where roughly constant mortality rate is experienced regardless of age. Some birds follow this pattern of survival.

In Type III curves, the greatest mortality is experienced early on in life, with relatively low rates of death for those surviving this bottleneck. This type of curve is characteristic of species that produce a large number of offspring. One example of a species that follows this type of survivorship curve is the cockroach.