Chapter 53 ~ Population Ecology

Changes to population size Adding & removing individuals from a populationAdding & removing individuals from a population –birth –death –immigration –emigr ation

Population characteristics Density ~ # of individuals per unit of area counts sample size estimate indirect indicators mark-recaptureDensity ~ # of individuals per unit of area counts sample size estimate indirect indicators mark-recapture Dispersion ~ pattern of spacing random ~ unpredictable, patternless spacing (a) clumped ~ patchy aggregation (b) uniform ~ even spacing (c)Dispersion ~ pattern of spacing random ~ unpredictable, patternless spacing (a) clumped ~ patchy aggregation (b) uniform ~ even spacing (c)

Demography: factors that affect growth & decline of populations Birthrate (natality, fecundity)~ # of offspring producedBirthrate (natality, fecundity)~ # of offspring produced Death rate (mortality)Death rate (mortality) Age structure ~ relative number of individuals of each ageAge structure ~ relative number of individuals of each age Survivorship curve ~ plot of numbers still alive at each ageSurvivorship curve ~ plot of numbers still alive at each age

Population Growth Models Exponential model (red) idealized population in an unlimited environment (J- curve); r-selected species (r=per capita growth rate)Exponential model (red) idealized population in an unlimited environment (J- curve); r-selected species (r=per capita growth rate) Logistic model (blue) carrying capacity (K): maximum population size that a particular environment can support (S-curve); K-selected speciesLogistic model (blue) carrying capacity (K): maximum population size that a particular environment can support (S-curve); K-selected species

Carrying capacity Can populations continue to grow exponentially?Can populations continue to grow exponentially? –of course NOT! –what sets limit? resources, predators, parasitesresources, predators, parasites Carrying Capacity (K)Carrying Capacity (K) –maximum population size that environment can support with no degradation of habitat not fixed; varies with changes in resourcesnot fixed; varies with changes in resources

Model of growth Decrease in rate of growth as reach carrying capacity

Population life history “strategies” r-selected (opportunistic)r-selected (opportunistic) Short maturation & lifespanShort maturation & lifespan Many (small) offspring; usually 1 (early) reproduction; no parental careMany (small) offspring; usually 1 (early) reproduction; no parental care High death rateHigh death rate K-selected (equilibrial) Long maturation & lifespan Few (large) offspring; usually several (late) reproductions; extensive parental care Low death rate

Different life strategies K-selectionK-selection r-selectionr-selection K-selection r-selection mortality constant

Population limiting factors Density-dependent factors competition predation stress/crowding waste accumulationDensity-dependent factors competition predation stress/crowding waste accumulation Density-independent factors weather/climate periodic disturbancesDensity-independent factors weather/climate periodic disturbances

Age structure Relative number of individuals of each ageRelative number of individuals of each age What do the data imply about population growth in these countries?

Human population What factors have contributed to this exponential growth pattern? 1650  500 million 2005  6 billion Is the human population reaching carrying capacity?