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Population Ecology Chapter 52.

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

1 Population Ecology Chapter 52

2 Study of populations in relation to environment
Environmental influences on: population density and distribution age structure variations in population size

3 Definition of Population:
Group of individuals of a single species living in the same general area

4 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

5 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 How do wildlife biologists approximate populations?

6 Estimating Wildlife Population Size
Defined Populations Undefined Populations

7 Density is the result of a dynamic interaction of
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. How do these factors Contribute to Population Size?? Births Deaths Immigration Emigration Figure 52.2

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

9 Clumped Dispersion Individuals aggregate in patches
May be influenced by resource availability and behavior

10 Uniform Dispersion Individuals are evenly distributed
May be influenced by social interactions such as territoriality

11 Random Dispersion Position of each individual is independent of other individuals (c) Random. Dandelions grow from windblown seeds that land at random and later germinate.

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

13 Semelparity: Big Bang Reproduce a single time and die Figure 52.6

14 Iteroparity – Repeated Reproduction
Produce offspring repeatedly over time

15 “Trade-offs” and Life Histories
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 Organisms have finite resources Which may lead to trade-offs between survival and reproduction RESULTS Kestrels: Produce a few eggs? Can invest more into each, ensuring greater survival Produce many eggs? Costly but if all survive, fitness is better

16 More is Better? 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.

17 Fewer is Better? 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.

18 Demography Study of the vital statistics of a population
And how they change over time Death rates and birth rates Zero population growth Occurs when the birth rate equals the death rate

19 Exponential Population Growth
Population increase under idealized conditions No limits on growth Under these conditions The rate of reproduction is at its maximum, called the intrinsic rate of increase

20 Example-understanding growth
Question: I offer you a job for 1 cent/day and your pay will double every day. You will be hired for 30 days. Will you take my job offer? Answer: If you said YES, you will have made $~21 million dollars for 30 days of work. How is this possible?????

21 1ST DAY OF WORK: 1 cent pay/day
30TH DAY OF WORK: ~10.2 million/day How is this possible????? Amount of Pay/Day # of Days

22 Exponential Growth Model
*Idealized population in an unlimited environment *Very rapid doubling time; steep J curve *r=N=(b-d)N t r=instrinsic rate of growth dN dt rmaxN

23 Exponential Growth in the Real World
Characteristic of some populations that are rebounding 1900 1920 1940 1960 1980 Year 2,000 4,000 6,000 8,000 Elephant population Cannot be sustained for long in any population

24 Logistic Population Growth
A more realistic population model Limits growth by incorporating carrying capacity

25 Logistic Population Growth
Carrying capacity (K) Is the maximum population size the environment can support In the logistic population growth model The per capita rate of increase declines as carrying capacity is reached

26 Logistic Growth Equation
Includes K, the carrying capacity dN dt (K  N) K rmax N

27 Logistic Population Growth
Produces a sigmoid (S-shaped) curve dN dt 1.0N Exponential growth Logistic growth 1,500  N 1,500 K  1,500 5 10 15 500 1,000 2,000 Number of generations Population size (N) Figure 52.12 dN dt (K  N) K rmax N

28 The Logistic Model and Real Populations
The growth of laboratory populations of paramecia Fits an S-shaped curve Figure 52.13a 800 600 400 200 Time (days) 5 10 15 (a) A Paramecium population in the lab. The growth of Paramecium aurelia in small cultures (black dots) closely approximates logistic growth (red curve) if the experimenter maintains a constant environment. 1,000 Number of Paramecium/ml

29 Logistic Growth and The Real World
Some populations overshoot K Before settling down to a relatively stable density Figure 52.13b 180 150 120 90 60 30 Time (days) 160 140 80 100 40 20 Number of Daphnia/50 ml (b) A Daphnia population in the lab. The growth of a population of Daphnia in a small laboratory culture (black dots) does not correspond well to the logistic model (red curve). This population overshoots the carrying capacity of its artificial environment and then settles down to an approximately stable population size.

30 Logistic Growth and the Real World
Some populations Fluctuate greatly around K Figure 52.13c 80 60 40 20 1975 1980 1985 1990 1995 2000 Time (years) Number of females (c) A song sparrow population in its natural habitat. The population of female song sparrows nesting on Mandarte Island, British Columbia, is periodically reduced by severe winter weather, and population growth is not well described by the logistic model.

31 The Logistic Model and Life Histories
Life history traits favored by natural selection May vary with population density and environmental conditions

32 Life History and Logistic Growth
K-selection, or density-dependent selection Selects for life history traits that are sensitive to population density Reproduce slowly, small litters r-selection, or density-independent selection Selects for life history traits that maximize reproduction Reproduce rapidly, large litters

33 Natural selection (diverse reproductive strategies)
a) Relatively few, large offspring (K selected species) b) Many, small offspring (r selected species) (K selected species) (r selected species)

34 Human Populations No population can grow indefinitely and humans are no exception 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

35 Global Carrying Capacity
Just how many humans can the biosphere support? Carrying capacity of earth is unknown….

36 Populations Regulated Biotic and Abiotic Factors
Two general questions we can ask about regulation of population growth What environmental factors stop a population from growing? 2. Why do some populations show radical fluctuations in size over time, while others remain stable?

37 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

38 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

39 Competition for Resources
In crowded populations, increasing population density Intensifies intraspecific competition for resources 10 100 1,000 10,000 Average number of seeds per reproducing individual (log scale) Average clutch size Seeds planted per m2 Density of females 70 20 30 40 50 60 80 2.8 3.0 3.2 3.4 3.6 3.8 4.0 (a) Plantain. The number of seeds produced by plantain (Plantago major) decreases as density increases. (b) Song sparrow. Clutch size in the song sparrow on Mandarte Island, British Columbia, decreases as density increases and food is in short supply. Figure 52.15a,b

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

41 Territoriality Example: Cheetas
Cheetahs are highly territorial Using chemical communication to warn other cheetahs of their boundaries Figure 52.16

42 Territoriality: Ocean birds
Exhibit territoriality in nesting behavior Figure 52.17

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

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

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

46 Population Dynamics The study of population dynamics
Focuses on the complex interactions between biotic and abiotic factors that cause variation in population size

47 Fluctuations in Population Size
Extreme fluctuations in population size Are typically more common in invertebrates than in large mammals Figure 52.19 1950 1960 1970 1980 Year 1990 10,000 100,000 730,000 Commercial catch (kg) of male crabs (log scale)

48 Metapopulations and Immigration
Groups of populations linked by immigration and emigration

49 Immigration- Movement Into a Population
High levels of immigration combined with higher survival can result in greater stability in populations Mandarte island Small islands Number of breeding females 1988 1989 1990 1991 Year 10 20 30 40 50 60 Figure 52.20

50 Population Cycles Many populations undergo regular boom-and-bust cycles Year 1850 1875 1900 1925 40 80 120 160 3 6 9 Lynx population size (thousands) Hare population size (thousands) Lynx Snowshoe hare Influenced by complex interactions between biotic and abiotic factors

51 The Global Human Population
The human population increased relatively slowly until about 1650 and then began to grow exponentially

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

53 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

54 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

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


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