# Population Ecology. Population Demographics Demographics are the various characteristics of a population including, Population Size, Age Structure, Density,

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Population Ecology

Population Demographics Demographics are the various characteristics of a population including, Population Size, Age Structure, Density, and Distribution Demographics allow one to determine the ecological and evolutionary relationships between various species populations

Population Size Population size is represented by the variable N Peterson Population Estimating is a common method for determining Population Size (N) Population Growth can be represented as either ‘exponential’ or ‘logistic’

Peterson Population Estimate The Peterson Estimate is a mark and recapture method divided into two sample periods (Precensus and Census)

Peterson Estimate Calculation During the Precensus, individuals are captured and marked (M) During the Census, individuals are captured, some of which have marks (R) and some which do not. The total captured on the Census equals (n). Peterson Estimate = (n x M) / R

Peterson Estimate Assumptions Assumes that no births, death, immigration, or emigration occur during the census period Assumes that mark are permanent and do not adversely effect the organism

Population Growth Factors that increase population size include ‘births’ an ‘immigration’ Factors that decrease population size include ‘deaths’ and ‘emigration’ The Net Reproductive Rate (r) r = [(births + immigration) – (deaths + emigration)]

Exponential Growth Population Growth (G) G = r x N New Population Value (N x ) N 1 = (r x N) + N N 2 = (r x N 1 ) + N 1

Logistic Growth Population Growth (G) G = r x N [(K-N) / K)] New Population Value (N x ) N 1 = (r x N [(K-N) / K)]) + N N 2 = (r x N 1 [(K-N 1 ) / K)]) + N 1

Age Structure Age structure is the number of individuals in each of several to many age categories

Population Density Population Density is the number of individuals in a specified area of a habitat

Population Distribution Population Distribution is the general pattern in which individuals or a population are dispersed through a specified area Clumped, Uniform, or Random

Survivorship Curves Type I High Survivorship until fairly late in life, then a large increase in death

Type II Fairly constant death rate at all ages

Type III Low survivorship early in life due to high death rate but if they reach adulthood they survive long

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