Population Ecology: Dynamics, Growth, and Regulation

1. Chap 52 Population Ecology

2. Population Ecology • The study of populations in their natural environment. • A populations environment affects the density, distribution, age structure and size.

3. 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

4. I. Density and Dispersion • All population sizes are limited by resources, space and mate availability. • Density is not a static property. Birth, death, immigration and emigration greatly affect a population at any given moment. • How the individuals within the population are spaced out indicates the dispersion of the population. • Environment and social interactions also contribute to variation in density

5. (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. Figure 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.

6. II. Life History results from Natural Selection • The traits that affect an organism’s reproduction and survival. • Life history patterns are very diverse. • Semelparity = “one shot” pattern of reproduction. • Iteroparity = repeated reproduction

7. Figure 52.6 An agave, or century plant

8. Population Growth and exponential model • Life histories provide a quantitative model for the understanding of population growth. • Population growth does not occur indefinitely for any species. • Factors such as resources, mates and space limit population growth.

9. EQUATION TIME!!!!!!!!!!!

10. Exponential Growth • Considers ideal conditions and unlimited resources. • The per capita rate of increase may assume the maximum rate for the species  r max. • The size of a population growing exponentially, increases at a constant rate, resulting in a J-shaped curve.

11. 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

12. Exponential growth assumes: • Continuous reproduction. • Environment is constant in space and time (unlimited resources). • All organisms are identical.

13. Logistic Growth Model • As population density increases, each individual has access to fewer resources. • There is a limit to the number of individuals that can occupy a habitat carrying capacity (K). • K is not fixed but fluxuates based on available resources.

14. If individuals cannot obtain sufficient resources to reproduce, (b) will decline. • If individuals cannot not find and consume enough energy to maintain themselves (m) may increase. • A decrease in (b) or increase in (m) results in a lower per capita rate of increase (r). • Therefore the per capita rate of increase declines as carrying capacity is reached.

15. Maximum Per capita rate of increase (r) Positive NK 0 Negative Population size (N) Figure 52.11 Influence of population size (N) on per capita rate of increase (r)

16. Logistic growth assumes: • Population growth rate declines when population #’s increase. • Population growth rate stops when N=K. • When N<K, population growth rates reach maximum intrinsic rate of increase. • When N>K, resources are limiting and growth rates become negative.

17. Table 52.3 A Hypothetical Example of Logistic Population Growth, Where K 1,000 and rmax 0.05 per Individual per Year

18. In the logistic model of growth, population increases the most during periods of intermediate size, when there is a substantial breeding population but also available space and resources available. • Logistic models produce a sigmoid (s-shaped) growth curve.

19. 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

20. K/R Selection • By connecting the favored life traits to the logistic model of population density, scientists have developed these terms. • K selection (density dependent)selection of life traits that are sensitive to population densities. • R selection (density independent) favors life traits that maximize reproductive success in low density environments.

21. K selection tends to maximize population size and operates in populations living at/near carrying capacity (K). • R selection tends to maximize the rate of increase (r) and operates in populations that fluxuate well below K.

23. Abiotic/Biotic Influence Populations • How do we regulate a population? • What environmental factors stop populations from growing? • Why do some populations show change over time while others remain stable? • Population dynamics focus on the abiotic/biotic factors that cause variation in population size.

24. To regulate population growth a negative feedback mechanism must exist between density and the vital rates of birth and death. • Many factors can cause a change in birth and death rates: • Competition for resources 5. Predation • Territoriality 6. Intrinsic factors • Health • Toxic waste

25. Age Structure • Diagram that shows present growth trends is a country’s age structure. • Commonly represented in “pyramids”. • Age structures not only predict a populations growth trends but also give a look into social conditions.

26. 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)