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Population Ecology

Explore the principles of population ecology, including the growth and sustainability of populations, with a focus on human population problems and their impact on resources. Learn about population size, age structure, density and distribution, as well as methods for determining population size. Discover the concepts of zero population growth, per capita rates, exponential and logistic growth, carrying capacity, and the effects of density-dependent and density-independent factors.

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Population Ecology

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  1. Population Ecology Chapter 27

  2. Population Ecology • Certain ecological principles govern the growth and sustainability of all populations • Human populations are no exception

  3. Limits to Growth • A population’s growth depends on the resources of its environment • Deer introduced to Angel Island • Population outstripped resources

  4. 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

  5. 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

  6. Population Age Structure • Divide population into age categories • Population’s reproductive base includes members of the reproductive and pre-reproductive age categories

  7. Density & Distribution • Number of individuals in some specified area of habitat • Crude density information is more useful if combined with distribution data clumped nearly uniform random

  8. 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

  9. 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

  10. 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

  11. Changes in Population Size • Immigration adds individuals • Emigration subtracts individuals • Births add individuals • Deaths subtract individuals

  12. net population growth rate per individual per unit time population growth per unit time number of individuals = X in-text, p. 688

  13. 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 stable

  14. 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

  15. 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

  16. 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

  17. Exponential Growth • Population size expands by ever increasing increments during successive intervals • The larger the population gets, the more individuals there are to reproduce

  18. Effect of Deaths • Population will grow exponentially as long as per capita death rates are lower than per capita birth rates 25% mortality between divisions

  19. Biotic Potential • Maximum rate of increase per individual under ideal conditions • Varies between species • In nature, biotic potential is rarely reached

  20. Limiting Factors • Any essential resource that is in short supply • All limiting factors acting on a population dictate sustainable population size

  21. 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

  22. Logistic Growth Equation G = rmaxN (K-N/K) • G = population growth per unit time • rmax = maximum population growth rate per unit time • N = number of individuals • K = carrying capacity

  23. Logistic Growth • As size of the population increases, rate of reproduction decreases • When the population reaches carrying capacity, population growth ceases carrying capacity Time

  24. Click to view animation. animation

  25. Overshooting Capacity • Population may temporarily increase above carrying capacity • Overshoot is usually followed by a crash; dramatic increase in deaths

  26. 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

  27. Density-Independent Controls • Factors unaffected by population density • Natural disasters or climate changes affect large and small populations alike

  28. initial carrying capacity new carrying capacity Fig. 40.6, p. 690

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