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Chapter 52: Population Ecology
What is a population? Individuals of a single species that occupy the same general area What is the difference between density & dispersion? Density – number of individuals per unit area or volume Dispersion – pattern of spacing within the boundaries of population
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Figure 52.2 Population dynamics
Factors that influence density….. Births and immigration add individuals to a population. Births Immigration PopuIation size Emigration Deaths Deaths and emigration remove individuals from a population. Increase Decrease
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Fig. 52.3 Patterns of dispersion within a population’s geographic range
(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. (c) Random. Dandelions grow from windblown seeds that land at random and later germinate. (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.
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Chapter 52: Population Ecology
What is a population? Individuals of a single species that occupy the same general area What is the difference between density & dispersion? Density – number of individuals per unit area or volume Dispersion – pattern of spacing within the boundaries of population What factors influence population size? Birth rate – fecundity Death rate Generation time Sex ratio 4. What do the survivorship curves mean?
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Figure 52.5 Idealized survivorship curves: Types I, II, and III
50 100 1 10 1,000 Percentage of maximum life span Number of survivors (log scale) Type I – most born survive & live to their maximum life span – us – k-selected Type II – constant death rate – each day has an equal opportunity for life or death Type III – high early death rate but survivors live to maximum life span – r-selected
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Chapter 52: Population Ecology
What is a population? What is the difference between density & dispersion? What factors influence population size? What do the survivorship curves mean? What are the 2 main populations growth curves? - Exponential – “J”-curve
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Figure 52.9 Population growth predicted by the exponential model
5 10 15 500 1,000 1,500 2,000 Number of generations Population size (N) dN dt 1.0N 0.5N dN = Δ population size dt = Δ time rmax = Births – deaths (intrinsic rate of increase) N = population size Species whose population size is primarily determined by birth rate = r-selected species
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Chapter 52: Population Ecology
What is a population? What is the difference between density & dispersion? What factors influence population size? What do the survivorship curves mean? What are the 2 main populations growth curves? Exponential Logistic
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Figure 52.12 Population growth predicted by the logistic model
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) K = carrying capacity Species whose population size is primarily determined by carrying capacity = k-selected species
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Chapter 52: Population Ecology
What is a population? What is the difference between density & dispersion? What factors influence population size? What do the survivorship curves mean? What are the 2 main populations growth curves? What is the difference between r-selected & k-selected species? r-selected (generalists) k-selected (equilibrial) Maturation time: short long Lifespan: short long Death rate high low Offspring/episode: many few Size of offspring/eggs: small large Parental care: none extensive Timing of 1st reproduction: early late in life Reproductions/lifetime: usually 1 several Examples: insects, fish, frogs mammals, birds 7. What factors limit a population?
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Chapter 52: Population Ecology
What is a population? What is the difference between density & dispersion? What factors influence population size? What do the survivorship curves mean? What are the 2 main populations growth curves? What is the difference between r-selected & k-selected species? 7. What factors limit a population? Density – dependent factors – intensify as population size increases Resource limitation Health Predation Waste accumulation Density – independent factors – effect population regardless of density Weather Climate Environmental disasters
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Figure 52.21 Population cycles in the snowshoe hare and lynx
Year 1850 1875 1900 1925 40 80 120 160 3 6 9 Lynx population size (thousands) Hare population size (thousands) Lynx Snowshoe hare
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Chapter 52: Population Ecology
What is a population? What is the difference between density & dispersion? What factors influence population size? What do the survivorship curves mean? What are the 2 main populations growth curves? What is the difference between r-selected & k-selected species? What factors limit a population? How has the human population changed & how is it shown?
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Figure 52.22 Human population growth (data as of 2003)
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
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Figure 52.25 Age-structure pyramids for the human population of three countries (data as of 2003)
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 Group NOT making babies Group making babies Babies Wide base = rapid growth Same width = slow growth Narrow base = decreasing
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