Presentation on theme: "Chapter 52 Earth’s Fluctuating Populations"— Presentation transcript:
1 Chapter 52 Earth’s Fluctuating Populations To understand human population growth we must consider the general principles of population ecology
2 PopulationA group of individuals of a single species living in the same general area
3 Density and Dispersion Density - the number of individuals per unit area or volumeDispersion - the pattern of spacing among individuals within the boundaries of the population
4 Population DynamicsDensity is the result of a dynamic interplay between processes that add individuals to a population and those that remove individuals from itImmigrationBirthsPopuIation sizeEmigrationDeaths
5 Patterns of Dispersion Clumped dispersionindividuals aggregate in patchesmay be influenced by resource availability and behaviorUniform dispersionindividuals are evenly distributedmay be influenced by social interactions such as territorialityRandom dispersionthe position of each individual is independent of other individuals
6 Life TableAge-specific summary of the survival pattern of a population
7 Survivorship CurveA graphic way of representing the data in a life tableFigure 52.41000100101Number of survivors (log scale)2468Age (years)MalesFemales
8 Semelparity “Big-bang” reproduction Reproduce a single time and die Figure 52.6
9 Iteroparity Repeated reproduction Produce offspring repeatedly over time
10 “Trade-offs” and Life Histories Two types of reproductive strategiesMany offspring with little energy put into each one.i.e. a plant that releases many small seedsFew offspring with more energy put into each one.i.e. a plant that releases less large seeds with a store of energy to help the seed surive and germinate
11 Exponential GrowthThe exponential model describes population growth in an idealized, unlimited environment
12 Exponential population growth results in a J-shaped curve Exponential growth is characteristic of some populations that are reboundingFigure 52.1019001920194019601980Year2,0004,0006,0008,000Elephant population
13 The Logistic Growth Model In the logistic population growth model the growth rate declines as carrying capacity is reachedCarrying capacity (K) is the maximum population size the environment can support800600400200Time (days)510151,000Number of Paramecium/mlThe logistic model of population growth produces a sigmoid (S-shaped) curve
14 Population Change and Population Density Density-independentBirth rate and death rate do not change with population densityDensity-dependentBirth rates fall and death rates rise with population density
15 Limiting Factors-factors that affect the carrying capacity Density-independent factorsWeather (storms, cold, drought)Some diseases (DDT poisoning)Density-dependent factorsFood or PredatorsSpace or ShelterOther diseases (rabies)
16 Population Cycles Many populations Undergo regular boom-and-bust cyclesFigure 52.21Year18501875190019254080120160369Lynx population size (thousands)Hare population size (thousands)LynxSnowshoe hareBoom-and-bust cycles are influenced by complex interactions between biotic and abiotic factors
17 The Global Human Population The human population increased relatively slowly until about 1650 and then began to grow exponentiallyFigure 52.228000 B.C.4000 B.C.3000 B.C.2000 B.C.1000 B.C.1000 A.D.The PlagueHuman population (billions)2000 A.D.123456
18 Though the global population is still growing The rate of growth began to slow approximately 40 years agoFigure 52.2319501975200020252050Year2003Percent increase220.127.116.11.18.104.22.168.21.8
19 Regional Patterns of Population Change To maintain population stabilityA regional human population can exist in one of two configurationsZero population growth = High birth rates – High death ratesZero population growth = Low birth rates – Low death rates
20 Population structureA population that is 75% adults, 25% juveniles is very different from a population of 25% adults and 75% juveniles.
21 Population structureAge structure – distribution of ages in a population.Size structure – distribution of sizes in a population.
22 Age structure is commonly represented in pyramids Figure 52.25Rapid growth AfghanistanSlow growth United StatesDecrease ItalyMaleFemaleAge8642Percent of population80–848575–7970–7465–6960–6455–5950–5445–4940–4435–3930–3420–2425–2910–145–90–415–19
23 Infant mortality and life expectancy at birth vary widely among developed and developing countries but do not capture the wide range of the human conditionFigure 52.26Developed countriesDeveloping countriesInfant mortality (deaths per 1,000 births)Life expectancy (years)60504030201080
24 Ecological footprints for 13 countries Show that the countries vary greatly in their footprint size and their available ecological capacityFigure 52.27161412108642New ZealandAustraliaCanadaSwedenWorldChinaIndiaAvailable ecological capacity (ha per person)SpainUKJapanGermanyNetherlandsNorwayUSAEcological footprint (ha per person)
25 At more than 6 billion people The world is already in ecological deficitNo population can exponentially grow foreverNo exceptions!
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