Chapter 52: Population Ecology

1. 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

2. Births and immigration add individuals to a population. Immigration Births PopuIationsize Emigration Deaths Deaths and emigration remove individuals from a population. Figure 52.2 Population dynamics Factors that influence density….. Increase Decrease

3. (a) Clumped. For many animals, such as thesewolves, living in groups increases theeffectiveness of hunting, spreads the workof protecting and caring for young, and helpsexclude other individuals from their territory. (c) Random. Dandelions grow from windblown seeds that land at random and later germinate. Fig. 52.3 Patterns of dispersion within a population’s geographic range (b) Uniform. Birds nesting on small islands, suchas these king penguins on South Georgia Islandin the South Atlantic Ocean, often exhibit uniformspacing, maintained by aggressive interactionsbetween neighbors.

4. 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?

5. 1,000 I 100 II Number of survivors (log scale) 10 III 1 100 50 0 Percentage of maximum life span Figure 52.5 Idealized survivorship curves: Types I, II, and III 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

6. 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

7. 2,000 dN  1.0N dt 1,500 dN  0.5N dt Population size (N) 1,000 500 0 0 10 15 5 Number of generations Figure 52.9 Population growth predicted by the exponential model 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

8. Self-Quiz • A uniform dispersion pattern for a population may indicate that • A. the population is spreading out and increasing its range. • B. resources are heterogeneously distributed. • C. individuals of the population are competing for some resource, such as water and minerals for plants or nesting sites for animals. • D. there is an absence of strong attractions or repulsions among individuals.

9. Self-Quiz • I would expect the potential for social interactions among individuals to be maximized when individuals • A. are randomly distributed in their environment. • B. are uniformly distributed in their environment. • C. have a clumped distribution in their environment. • D. are non-randomly distributed in their environment.

10. Self-Quiz • Humans are an example of an organism with a type I survivorship curve. This means • A. mortality rates are highest for younger individuals. • B. mortality rates are highest for older individuals. • C. mortality rates are constant over the life span of individuals. • D. the population growth rate is high.

11. Ticket Out the Door

12. 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

13. 2,000 dN  1.0N Exponential growth dt 1,500 K  1,500 Logistic growth Population size (N) 1,000 dN 1,500  N  1.0N dt 1,500 500 0 0 5 10 15 Number of generations Figure 52.12 Population growth predicted by the logistic model K = carrying capacity Species whose population size is primarily determined by carrying capacity = k-selected species

14. 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?

15. 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

16. Snowshoe hare 160 120 Lynx 9 Lynx population size (thousands) Hare population size (thousands) 80 6 40 3 0 0 1850 1875 1900 1925 Year Figure 52.21 Population cycles in the snowshoe hare and lynx

17. 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?

18. 6 5 4 Human population (billions) 3 2 The Plague 1 0 8000 B.C. 4000 B.C. 3000 B.C. 2000 B.C. 1000 B.C. 0 1000 A.D. 2000 A.D. Figure 52.22 Human population growth (data as of 2003)

19. Rapid growth Afghanistan Decrease Italy Slow growth United States Male Female Female Male Male Age Age Female 85 85 80–84 80–84 75–79 75–79 70–74 70–74 65–69 65–69 60–64 60–64 55–59 55–59 50–54 50–54 45–49 45–49 40–44 40–44 35–39 35–39 30–34 30–34 25–29 25–29 20–24 20–24 15–19 15–19 10–14 10–14 5–9 5–9 0–4 0–4 8 8 8 6 6 6 4 4 4 2 2 2 0 0 0 2 2 2 4 4 4 6 6 6 8 8 8 Percent of population Percent of population Percent of population Figure 52.25 Age-structure pyramids for the human population of three countries (data as of 2003) Group NOT making babies Group making babies Babies Wide base = rapid growth Same width = slow growth Narrow base = decreasing

20. Self-Quiz • A population’s carrying capacity is • A. the number of individuals in that population. • B. a constant that can be estimated for all populations. • C. inversely related to r. • D. The population size that can be supported by available resources for that species within the habitat.