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Population Dynamics Wildlife Management

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**Population Density Defined as total population size per unit of area.**

Population densities depend on: Interactions within the environment Quality of habitat

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**Density – Dependent Variables are variables whose effects increase with density and include:**

Food Water Shelter Disease

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**Density – Independent Variables affect the population regardless of size, and include:**

Habitat disruption Natural disaster Weather

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Carrying capacity is the maximum number of organisms that can be supported in a given habitat. This is often referred to by the variable “K”.

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**Populations can grow logistically or exponentially.**

Exponential growth is when the population growth stays the same, and so the population grows exponentially. Logistic growth slows as carrying capacity is reached.

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**Survivorship curves measure numbers of individuals in a population surviving at each age level.**

There are three survivorship curves – Type I loses the greatest numbers in old age. Type II has a steady rate of death. Type III loses the greatest numbers in infancy.

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**Reproductive Rates Reproductive rates are determined two ways.**

When carrying capacity (K) determines the rate of reproduction, this is called K – selected. When rates of reproduction (r) determine growth rate, this is r- selected.

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**r-selected (maximum growth rate, below carrying capacity)**

Early reproduction Short life span High mortality rate Little or no parental care Large investment in producing large numbers of offspring Below carrying capacity Examples include fish and grasshoppers.

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**K-selected (maximizes population size near carrying capacity)**

Late reproduction Long life span Low mortality rate Extensive parental care Greater investment in maintenance and survival of adults At or near carrying capacity Examples include sharks and elephants

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**Human Population Growth**

Human population growth does not currently show density effects that typically characterize natural populations. In natural populations, per capita population growth rate decreases with population size, whereas global human population growth rate has a positive relationship. Human population growth rate has been growing more than exponentially. Limited resources eventually will cause human population growth to slow, but global human carrying capacity is not known.

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