Transcript Chapter 35
Chapter 35 Population and Community Ecology Populations • Groups of organisms of the same species that live within a given area • Key characteristics: – Dispersion patterns – Population density – Growth rate Examples of Populations • All the e coli bacteria in a petri dish • All the rainbow trout in a stream • All the sunflowers in a prairie. Dispersion Patterns Within Populations Three common patterns of population distribution are: Sampling Techniques • Quadrats-mark off and survey a defined area • Indirect counting- counting nests or burrows, used to determine populations of difficult to find species. Ex. Mountain lion • Mark recapture Online biology activity • Distribution patterns go to online activity 35.1 Population Growth rate Exponential vs. Logistical Growth Survivorship in Populations Reproductive Strategies – Long life span • 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: • Bony fish • Grasshoppers • K-Selected (maximizes population size near carrying capacity) – – – – Late reproduction Low mortality rate Extensive parental care Greater investment in maintenance and survival of adults – At or near carrying capacity – Examples: • Sharks • Elephants Limits on Population Growth • Density Dependent Limits – Food – Water – Shelter – Disease • Density Independent Limits – Weather – Climate Boom and Bust Population growth Populations with boom and bust patterns have rapid growth and decline rates. Population Age Structure • Differences in environmental conditions and past history may cause populations to differ in their age distributions. • The future growth of a population depends on its current age distribution. 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. Density-Dependent and DensityIndependent Effects on Populations • In many habitats, the forces that limit population sizes are independent of population density. For example, extreme weather events may decrease populations. • For most species, density-dependent factors limit birth rates or increase death rates at least some of the time. This type of population determination often is referred to as “regulation.” • Disease outbreaks and starvation are two factors that may increase with population density. Interspecific relationships • Interspecific competition Interspecific relationships • Predation • Symbiotic relationships • Parasitism Mutualism • Commensalism go to online activity 35.4 Determining population size • Do this prelab activity before beginning the lab exercise