Population EcologySlide 2Limits to GrowthHuman Population ProblemsPopulationPopulation Age StructureDensity & DistributionDetermining Population SizeCapture-Recapture MethodAssumptions in Capture-RecaptureChanges in Population SizePowerPoint PresentationZero Population GrowthPer Capita RatesrExponential Growth EquationExponential GrowthEffect of DeathsBiotic PotentialLimiting FactorsCarrying Capacity (K)Logistic Growth EquationLogistic GrowthSlide 24Overshooting CapacityDensity-Dependent ControlsDensity-Independent ControlsSlide 28Population EcologyChapter 27Population Ecology•Certain ecological principles govern the growth and sustainability of all populations •Human populations are no exceptionLimits to Growth•A population’s growth depends on the resources of its environment•Deer introduced to Angel Island –Population outstripped resourcesHuman Population Problems•Over 6 billion people alive•About 2 billion live in poverty•Most resources are consumed by the relatively few people in developed countriesPopulation•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 structurePopulation Age Structure•Divide population into age categories•Population’s reproductive base includes members of the reproductive and pre-reproductive age categoriesDensity & Distribution•Number of individuals in some specified area of habitat•Crude density information is more useful if combined with distribution data clumpednearly uniformrandomDetermining Population Size•Direct counts are most accurate but seldom feasible•Can sample an area, then extrapolate•Capture-recapture method is used for mobile speciesCapture-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 populationAssumptions 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 timesChanges in Population Size•Immigration adds individuals•Emigration subtracts individuals•Births add individuals•Deaths subtract individualspopulation growth per unit timenet population growth rate per individual per unit timenumber of individuals= Xin-text, p. 688Zero 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 stablePer Capita Rates•Rates per individual•Total number of events in a time interval divided by the number of individuals•Per capita birth rate per month =Number of births per month Population sizer•Net reproduction per individual per unit time•Variable combines per capita birth and death rates (assuming both constant)•Can be used to calculate rate of growth of a populationExponential Growth EquationG = rN•G is population growth per unit time•r is net reproduction per individual per unit time•N is population sizeExponential Growth•Population size expands by ever increasing increments during successive intervals•The larger the population gets, the more individuals there are to reproduceEffect of Deaths•Population will grow exponentially as long as per capita death rates are lower than per capita birth rates 25% mortality between divisionsBiotic Potential•Maximum rate of increase per individual under ideal conditions•Varies between species•In nature, biotic potential is rarely reachedLimiting Factors•Any essential resource that is in short supply•All limiting factors acting on a population dictate sustainable population sizeCarrying Capacity (K)•Maximum number of individuals that can be sustained in a particular habitat•Logistic growth occurs when population size is limited by carrying capacityLogistic Growth Equation G = rmax N (K-N/K)•G = population growth per unit time•rmax = maximum population growth rate per unit time•N = number of individuals•K = carrying capacityLogistic Growth•As size of the population increases, rate of reproduction decreases•When the population reaches carrying capacity, population growth ceasescarrying capacityTimeanimationClick to view animation.Overshooting Capacity•Population may temporarily increase above carrying capacity•Overshoot is usually followed by a crash; dramatic increase in deathsDensity-Dependent Controls•Logistic growth equation deals with density-dependent controls•Limiting factors become more intense as population size increases•Disease, competition, parasites, toxic effects of waste productsDensity-Independent Controls•Factors unaffected by population density•Natural disasters or climate changes affect large and small populations alikeFig. 40.6, p. 690initial carrying capacitynew carrying
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