Population Ecology and Ecosystems Concepts and Applications Chapters 40 43 Basic Concepts Chapters 27 30 http darwin bio uci edu sustain bio65 lec16 b65lec16 htm Population Ecology Ecology Ecology The study of how organisms interact with one another and with their environment Certain ecological principles govern the growth and sustainability of all populations Human populations are no exception Population Ecology Human Population Problems Over 6 billion people alive About 2 billion live in poverty Most resources are consumed by the relatively few people in developed countries Population Ecology 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 Ecology Population Age Structure Divide population into age categories Population s reproductive base includes members of the reproductive and prereproductive age categories Population Ecology Density Distribution Number of individuals in some specified area of habitat Crude density information is more useful if combined with distribution data Fig 40 2 Population Ecology 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 Mark and Recapture marked Captured Total Captured Number released Total Pop Population Ecology 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 Population Ecology Changes in Population Size Immigration adds individuals Emigration subtracts individuals Births add individuals Deaths subtract individuals Population Ecology Zero Population Growth ZPG Interval in which number of births is balanced by number of deaths Assume no change as a result of migration Population size remains stable Population Ecology Per 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 size Population Ecology Exponential GrowthFig 40 4 Population size expands by ever increasing increments during successive intervals The larger the population gets the more individuals there are to reproduce Population Ecology r 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 population Population Ecology Exponential Growth Equation G rN G is population growth per unit time r is net reproduction per individual per unit time N is population size Population Ecology Biotic Potential Maximum rate of increase per individual under ideal conditions Varies between species In nature biotic potential is rarely reached Population Ecology Limiting Factors Any essential resource Space that is in short supply Food All limiting factors acting Shelter on a population dictate Temperature sustainable population Mates size Pollution Disease Population Ecology Carrying Capacity K Maximum number of individuals that can be sustained in a particular habitat Logistic growth occurs when population size is limited by carrying capacity Population Ecology Logistic 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 capacity Population Ecology Logistic Growth As size of the population increases rate of reproduction decreases When the population reaches carrying capacity population growth ceases Population Ecology Overshooting Capacity Population may temporarily increase above carrying capacity Overshoot is usually followed by a crash dramatic increase in deaths Fig 40 7 Population Ecology Resetting the Carrying Capacity Major changes in environment can change the carrying capacity of a local system Fig 40 6 Population Ecology Density 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 products Population Ecology Density Independent Controls Factors unaffected by population density Natural disasters or climate changes affect large and small populations alike Population Ecology Life History Patterns Patterns of timing of reproduction and survivorship Vary among species Summarized in survivorship curves and life tables Population Ecology Life Table Tracks age specific patterns Population is divided into age categories Birth rates and mortality risks are calculated for each age category Population Ecology Survivorship Curves Fig 40 8 Population Ecology Human Population Growth Population now exceeds 6 billion Rates of increase vary among countries Average annual increase is 1 26 percent Population continues to increase exponentially Human Population Growth Population Ecology Fig 40 9 p 695 Population Ecology How Humans have Side Stepped density dependent controls Expanded into new habitats Agriculture increased carrying capacity use of fossil fuels aided increase Hygiene and medicine lessened effects of density dependent controls Population Ecology Future Growth Exponential growth cannot continue forever Breakthroughs in technology may further increase carrying capacity Eventually densitydependent factors will slow growth Population Momentum Lowering fertility rates cannot immediately slow population growth rate Why If every couple had just two children population would still keep growing for another 60 years Population Ecology Resource Consumption United States has 4 7 percent of the world s population Americans have a disproportionately large effect on the world s resources Per capita Americans consume more resources and create more pollution than citizens of less developed nations Population Ecology Effects of Economic Development Total fertility rates TFRs are highest in developing countries lowest in developed countries When individuals are economically secure they are under less pressure to have large families Population Ecology Slowing Growth in China World s most extensive family planning program Government rewards small family size penalizes larger families provides free birth control abortion sterilization Since 1972 TFR down to 1 8 from 5 7 Community Ecology Community Ecology Community Populations of all species in a
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