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 (Nx)

N1 = (r x N) + N

N2 = (r x N1) + N1

Logistic Growth

• Population Growth (G)G = r x N [(K-N) / K)]

• New Population Value (Nx)

N1 = (r x N [(K-N) / K)]) + N

N2 = (r x N1 [(K-N1) / K)]) + N1

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