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Chapter 52 Earth’s Fluctuating Populations To understand human population growth we must consider the general principles of population ecology.

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Presentation on theme: "Chapter 52 Earth’s Fluctuating Populations To understand human population growth we must consider the general principles of population ecology."— Presentation transcript:

1 Chapter 52 Earth’s Fluctuating Populations To understand human population growth we must consider the general principles of population ecology

2 Population A group of individuals of a single species living in the same general area A 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 volume Density - the number of individuals per unit area or volume Dispersion - the pattern of spacing among individuals within the boundaries of the population Dispersion - the pattern of spacing among individuals within the boundaries of the population

4 Population Dynamics Density is the result of a dynamic interplay b etween processes that add individuals to a population and those that remove individuals from it Density is the result of a dynamic interplay b etween processes that add individuals to a population and those that remove individuals from it Births Immigration PopuIation size Emigration Deaths

5 Patterns of Dispersion Clumped dispersion Clumped dispersion individuals aggregate in patches individuals aggregate in patches may be influenced by resource availability and behavior may be influenced by resource availability and behavior Uniform dispersion Uniform dispersion individuals are evenly distributed individuals are evenly distributed may be influenced by social interactions such as territoriality may be influenced by social interactions such as territoriality Random dispersion Random dispersion the position of each individual is independent of other individuals the position of each individual is independent of other individuals

6 Life Table Age-specific summary of the survival pattern of a population Age-specific summary of the survival pattern of a population

7 Survivorship Curve A graphic way of representing the data in a life table A graphic way of representing the data in a life table Figure Number of survivors (log scale) Age (years) Males Females

8 Semelparity “Big-bang” reproduction “Big-bang” reproduction Reproduce a single time and die Reproduce a single time and die Figure 52.6

9 Iteroparity Repeated reproduction Repeated reproduction Produce offspring repeatedly over time Produce offspring repeatedly over time

10 “Trade-offs” and Life Histories Two types of reproductive strategies Two types of reproductive strategies Many offspring with little energy put into each one. Many offspring with little energy put into each one. i.e. a plant that releases many small seeds i.e. a plant that releases many small seeds Few offspring with more energy put into each one. Few 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 i.e. a plant that releases less large seeds with a store of energy to help the seed surive and germinate

11 Exponential Growth The exponential model describes population growth in an idealized, unlimited environment The exponential model describes population growth in an idealized, unlimited environment

12 Exponential population growth results in a J- shaped curve Exponential population growth results in a J- shaped curve Exponential growth i s characteristic of some populations that are rebounding Exponential growth i s characteristic of some populations that are rebounding Figure Year 0 2,000 4,000 6,000 8,000 Elephant population

13 The Logistic Growth Model In the logistic population growth model the growth rate declines as carrying capacity is reached In the logistic population growth model the growth rate declines as carrying capacity is reached Carrying capacity (K) is the maximum population size the environment can support Carrying capacity (K) is the maximum population size the environment can support Time (days) ,000 Number of Paramecium/ml The logistic model of population growth produces a sigmoid (S-shaped) curve The logistic model of population growth produces a sigmoid (S-shaped) curve

14 Population Change and Population Density Density-independent Density-independent Birth rate and death rate do not change with population density Birth rate and death rate do not change with population density Density-dependent Density-dependent Birth rates fall and death rates rise with population density Birth rates fall and death rates rise with population density

15 Limiting Factors-factors that affect the carrying capacity Density-independent factors Density-independent factors Weather (storms, cold, drought) Weather (storms, cold, drought) Some diseases (DDT poisoning) Some diseases (DDT poisoning) Density-dependent factors Density-dependent factors Food or Predators Food or Predators Space or Shelter Space or Shelter Other diseases (rabies) Other diseases (rabies)

16 Population Cycles Many populations Many populations Undergo regular boom-and-bust cycles Undergo regular boom-and-bust cycles Figure Year Lynx population size (thousands) Hare population size (thousands) Lynx Snowshoe hare Boom-and-bust cycles are influenced by complex interactions between biotic and abiotic factors Boom-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 exponentially The human population increased relatively slowly until about 1650 and then began to grow exponentially Figure B.C B.C B.C B.C B.C A.D. 0 The Plague Human population (billions) 2000 A.D

18 Though the global population is still growing Though the global population is still growing The rate of growth began to slow approximately 40 years ago The rate of growth began to slow approximately 40 years ago Figure Year 2003 Percent increase

19 Regional Patterns of Population Change To maintain population stability To maintain population stability A regional human population can exist in one of two configurations A regional human population can exist in one of two configurations Zero population growth = High birth rates – High death rates Zero population growth = High birth rates – High death rates Zero population growth = Low birth rates – Low death rates Zero population growth = Low birth rates – Low death rates

20 Population structure A population that is 75% adults, 25% juveniles is very different from a population of 25% adults and 75% juveniles.

21 Population structure Age structure – distribution of ages in a population. Age structure – distribution of ages in a population. Size structure – distribution of sizes in a population. Size structure – distribution of sizes in a population.

22 Age structure is commonly represented in pyramids Age structure is commonly represented in pyramids Figure Rapid growth Afghanistan Slow growth United States Decrease Italy Male Female Male FemaleMale Female Age Percent of population 80–84 85  75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 20–24 25–29 10–14 5–9 0–4 15–19 80–84 85  75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 20–24 25–29 10–14 5–9 0–4 15–19

23 Infant mortality and life expectancy at birth v ary widely among developed and developing countries but do not capture the wide range of the human condition Infant mortality and life expectancy at birth v ary widely among developed and developing countries but do not capture the wide range of the human condition Figure Developed countries Developing countries Developed countries Developing countries Infant mortality (deaths per 1,000 births) Life expectancy (years)

24 Ecological footprints for 13 countries Ecological footprints for 13 countries Show that the countries vary greatly in their footprint size and their available ecological capacity Show that the countries vary greatly in their footprint size and their available ecological capacity Figure New Zealand Australia Canada Sweden World China India Available ecological capacity (ha per person) Spain UK Japan Germany Netherlands Norway USA Ecological footprint (ha per person)

25 At more than 6 billion people At more than 6 billion people The world is already in ecological deficit The world is already in ecological deficit No population can exponentially grow forever No population can exponentially grow forever No exceptions! No exceptions!


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