2Population Density Defined as total population size per unit of area. Population densities depend on:Interactions within the environmentQuality of habitat
3Density – Dependent Variables are variables whose effects increase with density and include: FoodWaterShelterDisease
4Density – Independent Variables affect the population regardless of size, and include: Habitat disruptionNatural disasterWeather
5Carrying capacity is the maximum number of organisms that can be supported in a given habitat. This is often referred to by the variable “K”.
6Populations 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.
8Survivorship 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.
10Reproductive 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.
11r-selected (maximum growth rate, below carrying capacity) Early reproductionShort life spanHigh mortality rateLittle or no parental careLarge investment in producing large numbers of offspringBelow carrying capacityExamples include fish and grasshoppers.
12K-selected (maximizes population size near carrying capacity) Late reproductionLong life spanLow mortality rateExtensive parental careGreater investment in maintenance and survival of adultsAt or near carrying capacityExamples include sharks and elephants
13Human 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.