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Unformatted text preview: POPULATION ECOLOGY ECOLOGY Chapter 45 Impacts, Issues: The Numbers Impacts, Game Game St. Matthew Island is an example of how St. population growth depends on limited environmental resources environmental In 1944, US Coast Guard was stationed In on the island along with 29 reindeer, as an emergency food supply an Impacts, Issues: The Numbers Impacts, Game Game Without natural predators, reindeer population grew and depleted Without the island’s lichen After a harsh winter, all but 1% of the founding herd perished - by After the 1980s, no reindeer were left the Today, soaring Whitetail deer populations are overwhelming their Today, environment in North America - damaging the habitat environment Principles of Ecology help us understand population dynamics Principles and address population-related problems such as Whitetail deer and Fig. 45-1, p.800 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 Size,Density & Distribution • Size = Number of individuals that contribute to the gene pool. Density = Number of individuals in some specified area of habitat Distribution = Pattern the individuals are dispersed in an area. Crude density information is more useful if combined with distribution data random • • clumped nearly uniform • Fig. 45-2a, p.802 Changes in Population Size • Immigration adds individuals • Emigration subtracts individuals • Births add individuals • Deaths subtract individuals Exponential Growth • Population size expands by ever increasing increments during successive intervals • The larger the population gets, the more individuals there are to reproduce Fig. 45-5a, p.804 Limiting Factors • Any essential resource that is in short supply • All limiting factors acting on a population dictate sustainable population size • CARRYING CAPACITY = The maximum number of individuals that can be sustained in a particular habitat. Overshooting Capacity • Population may temporarily increase above carrying capacity • Overshoot is usually followed by a crash; dramatic increase in deaths Reindeer on St. Matthew’s Island Fig. 45-9, p.807 Density Controls DENSITY DEPENDENT CONTROLS • • Limiting factors become more intense as population size increases Disease, competition, parasites, products toxic effects of waste DENSITY INDEPENDENT CONTROLS . . Factors unaffected by population density Natural disasters or climate changes affect large and small populations alike. Life History Patterns • Patterns of timing of reproduction and survivorship • Vary among species • Summarized in survivorship curves and life tables Survivorship Curves Graph of age-specific survivorship (Page 809) ie: Elephants ie:Birds ie:Insects or Sea Stars Figure 45.11 Page 809 Predation and Life History • Guppy populations vary in life history characteristics and morphology • Differences have genetic basis • Variation seems to be result of directional selection by predators GUPPY FROM A PIKE-CICHLID STREAM Guppies from Pike/Cichlid streams grow faster, are smaller at maturity, and reproduce earlier than Guppies that are from streams with Killifish as the predator (p810) Fig. 45-12b1, p.810 Population Ecology Certain ecological principles govern the growth and sustainability of all populations--including human populations Biotic Potential • Maximum rate of increase per individual under ideal conditions • Varies between species • In nature, biotic potential is rarely reached 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 HUMANS SIDE-STEPPING CONTROLS • • • Expanded into new habitats Agriculture increased carrying capacity; use of fossil fuels aided increase Hygiene and medicine lessened effects of density-dependent controls Future Growth • Exponential growth cannot continue forever • Breakthroughs in technology may further increase carrying capacity • Eventually, density-dependent factors will slow growth Population Age Structure • Divide population into age categories • Population’s reproductive base includes members of the reproductive and prereproductive age categories Age Structure Diagrams Show age distribution of a population Rapid Growth Slow Growth Zero Growth Negative Growth Fertility rates and Effects of Economic Development • Total fertility rate (TFR) is average number of children born to a woman • Worldwide, average annual rate of increase is 1.26% • (it took 2.5my for the human population to reach 1b., only 200y later it is over 6b.) • 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 Fig. 45-17b, p.815 THINK ABOUT THE NEXT THREE SLIDES: SLIDES: Population Momentum Lowering fertility rates cannot Lowering immediately slow population growth rate immediately Why? There are already many future Why? parents alive parents If every couple had just two children, If population would still keep growing for another 60 years another Resource Consumption Resource United States has 4.7 percent of the United world’s population world’s Americans have a disproportionately Americans large effect on the world’s resources large Per capita, Americans consume more Per resources and create more pollution than citizens of less developed nations citizens No Growth No As Baby Boomers retire, the percentage As in the 65-and-older bracket increases in With better health care, people are living With longer longer As the older population swells, they As continue to consume -- who will carry the economic burden? economic ...
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