PopulationEcology-SacramentoState.ppt

Population Ecology Chapter 39 Ecology - Definition The science of the relationships between organisms and their environments. or The interactions that organisms have with other organisms and with their environment. Population A group of individuals of the same species occupying a given area Can be described by demographics Vital statistics such as size, density, distribution, and age structure Population Age Structure Divide population into age categories Pre-reproductive Reproductive Post-reproductive Population’s reproductive base includes members of the reproductive and pre-reproductive age categories Density Distribution Number of individuals in some specified area of habitat Crude density information is more useful if combined with distribution data Determining Population Size Direct counts are most accurate but seldom feasible Can sample an area, then extrapolate Capture-recapture method is used for mobile species Capture-Recapture Method Capture, mark, and release individuals Return later and capture second sample Count the number of marked individuals and use this to estimate total population Assumptions in Capture-Recapture Marking has no effect on mortality Marking has no effect on likelihood to being captured There is no immigration or emigration between sampling times Changes in Population Size Immigration adds individuals Emigration subtracts individuals Births add individuals Deaths subtract individuals Zero Population Growth Interval in which number of births is balanced by number of deaths Assume no change as a result of migration Population size remains Exponential Growth Population size expands by ever increasing increments during successive intervals The larger the population gets, the more individuals there are to reproduce Biotic Potential Maximum rate of increase per individual under ideal conditions Varies between species In nature, biotic potential is rarely reached Biotic Potential Which has greater biotic potential, Elephants or frogs