Population Ecology 2013-14

Population EcologyCertain ecological principles govern the growth and sustainability of all populations--including human populations

Ecological Principles Apply to All SpeciesHumans, Palms, Crabs, Seagulls, algae, etc.

Limits to GrowthA populations growth depends on the resources of its environmentDeer introduced to Angel Island Population outstripped resources

Angel Island

Angel Island 1A. Angel Island is a game reserve in San Francisco Bay near SausalitoB. In the early 1900's well-meaning nature lovers introduced deer to the islandC. With no natural predators to control them the population quickly rose to a level much higher than the island could supportD. Well meaning people brought food to the island to feed the deer, causing the population to further increase

Angel Island 2E. Eventually the population grew to over 300, much too large for the island to supportF. As the deer began to starve they ate most of the native vegetation. Without vegetation the soil started washing away and the island environment rapidly deteriorated

Angel Island - 3G. It was proposed that hunters kill some of the deer and/or that coyotes, the deers natural predators, be introduced to the island. However many people objected because they viewed both alternatives as cruelH. Eventually two thirds of the population was rounded up and moved to the mainland, at a cost of $3,000 per deer

Angel Island - 4I. However, tracking studies revealed that the majority of the deer moved to the mainland were killed by cars, dogs, coyotes and hunters within 60 days

J. The story of Angel Island illustrates a basic ecological principle: a population's growth is dependent on the resources of its environment. Human intervention could only postpone, not prevent the inevitable

Angel Island - 5K. Many environmental problems are simply the result of a lack of understanding of basic ecological principles by politicians, lawyers, economists, the general public and even well intentioned "environmentalists". Human ignorance of simple ecological principles often leads to disastrous results

From: http://arnica.csustan.edu/boty1050/Ecology/ecology.htm

Human Population ProblemsOver 7 billion people aliveAbout 2 billion live in povertyMost resources are consumed by the relatively few people in developed countries

Population GrowthFor most of human history, humans have not been very numerous compared to other species.It took all of human history to reach 1 billion.150 years to reach 3 billion.12 years to go from 5 to 6 billion.Less than 12 years to go from 6 to 7 billion.Human population tripled during the twentieth century.

World Population Growth VisualizedFrom youtube

http://www.youtube.com/watch?v=4BbkQiQyaYc

Human Population History

Seven Billion..From the National Geographic:http://www.youtube.com/watch?v=sc4HxPxNrZ0

U.S. POPClock Projection

According to the U.S. Bureau of the Census, the resident population of the United States, projected to 03/21/05 at 17:04 GMT (EST+5) is 295,707,750COMPONENT SETTINGSOne birth every.................................. 7 seconds One death every.................................. 11 seconds One international migrant (net) every............ 24 seconds Net gain of one person every..................... 12 seconds

So what do you think the US population is today?

US PopClock todayhttp://www.census.gov/population/www/popclockus.html

PopulationA group of individuals of the same species occupying a given area during a particular period of timeCan be described by demographicsVital statistics such as size, density, distribution, and age structure

Population Age StructureDivide population into age categoriesPopulations reproductive base includes members of the reproductive and pre-reproductive age categories

Population Age Structure Diagram

Density & DistributionNumber of individuals in some specified area of habitatCrude density information is more useful if combined with distribution data clumpednearly uniformrandomFigure 45.2Page 808

Clumped Distribution

Determining Population SizeDirect counts are most accurate but seldom feasibleCan sample an area, then extrapolateCapture-recapture method is used for mobile species

Population EstimateHow could you determine the population size of the students in Robinson Hall?

The number of revelers on the beach?

Does Time and Place Make a Difference?Daytona BeachHilton Head

Capture-Recapture MethodCapture, mark, and release individualsReturn later and capture second sampleCount the number of marked individuals and use this to estimate total population

Example:Capture - RecaptureIn 1970, naturalists wanted to estimate the number of pickerel fish in Dryden Lake in central New York State. They captured 232 pickerel, put a mark on their fins, and returned the fish to the lake. Several weeks later, another sample of 329 pickerel fish were captured. Of this second sample, 16 had marks on their fins. (Chaterjee in Mosteller et al. Statistics by Example: Finding Models).

Chain Pickerel

How Many Pickerel Were in the Lake?N = total number of pickerel in lakeNM = total number of marked pickerel (232)RC = Number of recaptured pickerel (16)NS = number of fish in sample (329)

NM/N = RC/NSN = (NM x NS)/RC

Solution N = (232 x 329)/16

N = 4770 pickerel in the lake (estimate)

This is an example of how the Capture/Recapture method works.

AssumptionsThe sampling is randomThe marked organisms will not be harmed by the capture and markingsThe marked organisms will not avoid recaptureThe samples are statistically large enough to avoid problems with sampling errorNo significant emigration/immigration occursThe sampling is done promptly

Changes in Population SizeImmigration adds individualsEmigration subtracts individualsBirths add individualsDeaths subtract individuals

Zero Population GrowthInterval in which number of births is balanced by number of deathsAssume no change as a result of migrationPopulation size remains stable

Per Capita RatesRates per individualTotal number of events in a time interval divided by the number of individualsPer capita birth rate per month =Number of births per month Population size

rNet reproduction per individual per unit time (Intrinsic rate of natural increase) a constant the units are inverse timeVariable combines per capita birth and death rates (assuming both constant)Can be used to calculate rate of growth of a population

Exponential Growth EquationG = rN

G is population growth per unit timer is net reproduction per individual per unit timeN is population size

Exponential GrowthPopulation size expands by ever increasing increments during successive intervalsThe larger the population gets, the more individuals there are to reproduceFigure 45.4Page 810

(r) Strategies

Short lifeRapid growthEarly maturityMany small offspring.Little parental care.Little investment in individual offspring.

Adapted to unstable environment.Pioneers, colonizersNiche generalistsPreyRegulated mainly by extrinsic factors.Low trophic level.

Weedy Species r StrategistsOpportunistic Species - Quickly appear when opportunities arise.Many weeds.Pioneer Species - Can quickly colonize open, disturbed, or bare ground.

Effect of DeathsPopulation grows exponentially as long as per capita death rates are lower than per capita birth rates 25% mortality between divisions Figure 45.5Page 811

Biotic PotentialMaximum rate of increase per individual under ideal conditionsVaries between speciesIn nature, biotic potential is rarely reached

Limiting FactorsAny essential resource that is in short supplyAll limiting factors acting on a population dictate sustainable population size

Carrying Capacity (K)Maximum number of individuals that can be sustained in a particular habitatLogistic growth occurs when population size is limited by carrying capacity

Logistic Growth Equation G = rmax N ((K-N)/K)G = population growth per unit timermax = maximum population growth rate per unit timeN = number of individualsK = carrying capacity

Logistic GrowthAs size of the population increases, rate of reproduction decreases

When the population reaches carrying capacity, population growth ceases

Figure 45.6Page 812initial carrying capacitynew carrying capacityLogistic Growth Graph

K StrategistsLong lifeSlower growthLate maturityFewer large offspring.High parental care and protection.High investment in individual offspring.

More on K StrategistsAdapted to stable environment.Later stages of succession.Niche specialistsPredators (often, but not always)Regulated mainly by intrinsic factors.High trophic level.

Top Predators

Overshooting CapacityPopulation may temporarily increase above carrying capacityOvershoot is usually followed by a crash; dramatic increase in deathsFigure 45.6Page 812Reindeer on St. Matthews Island

Density-Dependent ControlsLogistic growth equation deals with density-dependent controlsLimiting factors become more intense as population size increasesDisease, competition, parasites, toxic effects of waste products

Density-Independent ControlsFactors unaffected by population densityNatural disasters or climate changes affect large and small populations alike

A Hurricane is an Example of a Density Independent Factor

Earth Quakes and Tsunamis

Life History PatternsPatterns of timing of reproduction and survivorshipVary among speciesSummarized in survivorship curves and life tables

Life TableTracks age-specific patterns Population is divided into age categoriesBirth rates and mortality risks are calculated for each age category

USA

Survivorship CurvesGraph of age-specific survivorship Figure 45.8Page 815

Type ILarge animals, few offspring, much parental care, live to an old age

Type IIBirds are good examples Intermediate number of offspring, some parental care, fairly constant survival rate over a life time.

Type IIIThese are typical r strategists, weedy species, pesky..Short life, many offspring, little parental care, high mortality of theyoung

Predation and Life History Guppy populations vary in life history characteristics and morphologyDifferences have genetic basisVariation seems to be result of directional selection by predators

Human Population Growth Population now exceeds 6 billionRates of increase vary among countriesAverage annual increase is 1.26 percentPopulation continues to increase exponentially

Side-Stepping ControlsExpanded into new habitats Agriculture increased carrying capacity; use of fossil fuels aided increaseHygiene and medicine lessened effects of density-dependent controls

Future GrowthExponential growth cannot continue foreverBreakthroughs in technology may further increase carrying capacity Eventually, density-dependent factors will slow growth

Fertility Rates Worldwide, average annual rate of increase is 1.26%Total fertility rate (TFR) is average number of children born to a womanHighest in developing countries, lowest in developed countries

Age Structure DiagramsShow age distribution of a populationRapid GrowthSlow GrowthZero GrowthNegative GrowthFigure 45.14Page 821

Population MomentumLowering fertility rates cannot immediately slow population growth rateWhy? There are already many future parents aliveIf every couple had just two children, population would still keep growing for another 60 years

Projected Human Populations

Life Expectancy and Income

Slowing Growth in ChinaWorlds most extensive family planning program Government rewards small family size, penalizes larger families, provides free birth control, abortion, sterilizationSince 1972, TFR down to 1.8 from 5.7

Effects of Economic Development Total fertility rates (TFRs) are highest in developing countries, lowest in developed countriesWhen individuals are economically secure, they are under less pressure to have large families

Sweat Shop, Indiahttp://www.mcps.k12.md.us/curriculum/socialstd/grade7/india/Sweatshop.htmlShop size = 2m x 5m. How many people can you count?

Population Sizes in 2001Asia3.7 billionEurope727 millionAfrica816 millionLatin America525 millionNorth America316 millionOceania31 million

Population 2008

Asia 4.1 billionEurope 732 millionAfrica 973 millionLatin America 577 millionNorth America 337 millionOceania 34 millionhttp://en.wikipedia.org/wiki/World_population

Demographic Transition ModelBased on historical data from western EuropePostulates that as countries become industrialized, first death rates drop, then birth rates drop

Demographic Transition ModelStage 1 PreindustrialStage 2 TransitionalStage 3 IndustrialStage 4 Postindustrialbirthsdeathsrelative population sizelowincreasingvery highdecreasinglowzeronegativeFigure 45.16Page 822

Resource ConsumptionUnited States has 4.7 percent of the worlds populationAmericans have a disproportionately large effect on the worlds resourcesPer capita, Americans consume more resources and create more pollution than citizens of less developed nations

Population EcologyThe End

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