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Chapter 52 Population Ecology.

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Presentation on theme: "Chapter 52 Population Ecology."— Presentation transcript:

1 Chapter 52 Population Ecology

2 Overview: Earth’s Fluctuating Populations
To understand human population growth We must consider the general principles of population ecology

3 Population ecology is the study of populations in relation to environment
Including environmental influences on population density and distribution, age structure, and variations in population size

4 Concept 52.1: Dynamic biological processes influence population density, dispersion, and demography
A population Is a group of individuals of a single species living in the same general area

5 Density and Dispersion
Is the number of individuals per unit area or volume Dispersion Is the pattern of spacing among individuals within the boundaries of the population

6 Density: A Dynamic Perspective
Determining the density of natural populations Is possible, but difficult to accomplish In most cases It is impractical or impossible to count all individuals in a population

7 Density is the result of a dynamic interplay
Between processes that add individuals to a population and those that remove individuals from it Births and immigration add individuals to a population. Births Immigration PopuIation size Emigration Deaths Deaths and emigration remove individuals from a population. Figure 52.2

8 Patterns of Dispersion
Environmental and social factors Influence the spacing of individuals in a population

9 A clumped dispersion Is one in which individuals aggregate in patches
May be influenced by resource availability and behavior Figure 52.3a (a) Clumped. For many animals, such as these wolves, living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory.

10 A uniform dispersion Is one in which individuals are evenly distributed May be influenced by social interactions such as territoriality Figure 52.3b (b) Uniform. Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors.

11 A random dispersion Is one in which the position of each individual is independent of other individuals (c) Random. Dandelions grow from windblown seeds that land at random and later germinate. Figure 52.3c

12 Demography is the study of the vital statistics of a population
And how they change over time Death rates and birth rates Are of particular interest to demographers

13 Survivorship Curves A survivorship curve
Is a graphic way of representing the data in a life table

14 The survivorship curve for Belding’s ground squirrels
Shows that the death rate is relatively constant Figure 52.4 1000 100 10 1 Number of survivors (log scale) 2 4 6 8 Age (years) Males Females

15 Survivorship curves can be classified into three general types
Type I, Type II, and Type III I II III 50 100 1 10 1,000 Percentage of maximum life span Number of survivors (log scale) Figure 52.5

16 A reproductive table, or fertility schedule
Reproductive Rates A reproductive table, or fertility schedule Is an age-specific summary of the reproductive rates in a population

17 Concept 52.2: Life history traits are products of natural selection
Life history traits are evolutionary outcomes Reflected in the development, physiology, and behavior of an organism

18 Species that exhibit semelparity, or “big-bang” reproduction
Reproduce a single time and die Figure 52.6

19 Species that exhibit repeated reproduction
Produce offspring repeatedly over time

20 Parental care of smaller broods
May also facilitate survival of offspring

21 “Trade-offs” and Life Histories
Organisms have finite resources Researchers in the Netherlands studied the effects of parental caregiving in European kestrels over 5 years. The researchers transferred chicks among nests to produce reduced broods (three or four chicks), normal broods (five or six), and enlarged broods (seven or eight). They then measured the percentage of male and female parent birds that survived the following winter. (Both males and females provide care for chicks.) EXPERIMENT The lower survival rates of kestrels with larger broods indicate that caring for more offspring negatively affects survival of the parents. CONCLUSION 100 80 60 40 20 Reduced brood size Normal brood size Enlarged brood size Parents surviving the following winter (%) Male Female Which may lead to trade-offs between survival and reproduction RESULTS Figure 52.7

22 Some plants produce a large number of small seeds
Ensuring that at least some of them will grow and eventually reproduce Figure 52.8a (a) Most weedy plants, such as this dandelion, grow quickly and produce a large number of seeds, ensuring that at least some will grow into plants and eventually produce seeds themselves.

23 Other types of plants produce a moderate number of large seeds
That provide a large store of energy that will help seedlings become established Figure 52.8b (b) Some plants, such as this coconut palm, produce a moderate number of very large seeds. The large endosperm provides nutrients for the embryo, an adaptation that helps ensure the success of a relatively large fraction of offspring.

24 It is useful to study population growth in an idealized situation
Concept 52.3: The exponential model describes population growth in an idealized, unlimited environment It is useful to study population growth in an idealized situation In order to understand the capacity of species for increase and the conditions that may facilitate this type of growth

25 Per Capita Rate of Increase
If immigration and emigration are ignored A population’s growth rate (per capita increase) equals birth rate minus death rate

26 Zero population growth
Occurs when the birth rate equals the death rate The population growth equation can be expressed as dN dt rN

27 Exponential population growth
Exponential Growth Exponential population growth Is population increase under idealized conditions Under these conditions The rate of reproduction is at its maximum, called the intrinsic rate of increase

28 Exponential population growth
Results in a J-shaped curve Figure 52.9 5 10 15 500 1,000 1,500 2,000 Number of generations Population size (N) dN dt 1.0N 0.5N

29 The J-shaped curve of exponential growth
Is characteristic of some populations that are rebounding Figure 52.10 1900 1920 1940 1960 1980 Year 2,000 4,000 6,000 8,000 Elephant population

30 A more realistic population model
Concept 52.4: The logistic growth model includes the concept of carrying capacity Exponential growth Cannot be sustained for long in any population A more realistic population model Limits growth by incorporating carrying capacity

31 Carrying capacity (K) Is the maximum population size the environment can support

32 There are two general questions we can ask
Concept 52.5: Populations are regulated by a complex interaction of biotic and abiotic influences There are two general questions we can ask About regulation of population growth

33 What environmental factors stop a population from growing?
Why do some populations show radical fluctuations in size over time, while others remain stable?

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

35 Density-Dependent Population Regulation
Density-dependent birth and death rates Are an example of negative feedback that regulates population growth Are affected by many different mechanisms

36 In many vertebrates and some invertebrates
Territoriality In many vertebrates and some invertebrates Territoriality may limit density

37 Cheetahs are highly territorial
Using chemical communication to warn other cheetahs of their boundaries Figure 52.16

38 Oceanic birds Exhibit territoriality in nesting behavior Figure 52.17

39 Health Population density In dense populations
Can influence the health and survival of organisms In dense populations Pathogens can spread more rapidly

40 As a prey population builds up
Predation As a prey population builds up Predators may feed preferentially on that species

41 The accumulation of toxic wastes
Can contribute to density-dependent regulation of population size

42 Intrinsic Factors For some populations
Intrinsic (physiological) factors appear to regulate population size

43 Population Cycles Many populations
Undergo regular boom-and-bust cycles Figure 52.21 Year 1850 1875 1900 1925 40 80 120 160 3 6 9 Lynx population size (thousands) Hare population size (thousands) Lynx Snowshoe hare

44 Boom-and-bust cycles Are influenced by complex interactions between biotic and abiotic factors

45 No population can grow indefinitely
Concept 52.6: Human population growth has slowed after centuries of exponential increase No population can grow indefinitely And humans are no exception

46 The Global Human Population
The human population Increased relatively slowly until about 1650 and then began to grow exponentially Figure 52.22 8000 B.C. 4000 B.C. 3000 B.C. 2000 B.C. 1000 B.C. 1000 A.D. The Plague Human population (billions) 2000 A.D. 1 2 3 4 5 6

47 Though the global population is still growing
The rate of growth began to slow approximately 40 years ago Figure 52.23 1950 1975 2000 2025 2050 Year 2003 Percent increase 2.2 2 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 1.8

48 Regional Patterns of Population Change
To maintain population stability A regional human population can exist in one of two configurations

49 Zero population growth = High birth rates – High death rates
Zero population growth = Low birth rates – Low death rates

50 The demographic transition
Is the move from the first toward the second state Figure 52.24 50 40 20 30 10 1750 1800 1850 1900 1950 2000 2050 Birth rate Death rate Year Sweden Mexico Birth or death rate per 1,000 people

51 The demographic transition
Is associated with various factors in developed and developing countries

52 One important demographic factor in present and future growth trends
Age Structure One important demographic factor in present and future growth trends Is a country’s age structure, the relative number of individuals at each age

53 Age structure Is commonly represented in pyramids Figure 52.25
Rapid growth Afghanistan Slow growth United States Decrease Italy Male Female Age 8 6 4 2 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

54 Age structure diagrams
Can predict a population’s growth trends Can illuminate social conditions and help us plan for the future

55 Infant Mortality and Life Expectancy
Infant mortality and life expectancy at birth Vary widely among developed and developing countries but do not capture the wide range of the human condition Figure 52.26 Developed countries Developing countries Infant mortality (deaths per 1,000 births) Life expectancy (years) 60 50 40 30 20 10 80

56 Global Carrying Capacity
Just how many humans can the biosphere support?

57 Estimates of Carrying Capacity
The carrying capacity of Earth for humans is uncertain

58 The ecological footprint concept
Summarizes the aggregate land and water area needed to sustain the people of a nation Is one measure of how close we are to the carrying capacity of Earth

59 Ecological footprints for 13 countries
Show that the countries vary greatly in their footprint size and their available ecological capacity Figure 52.27 16 14 12 10 8 6 4 2 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)

60 At more than 6 billion people
The world is already in ecological deficit

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