CHAPTER 35 Population Dynamics

1. CHAPTER 35Population Dynamics Modules 35.1 – 35.5

2. The Spread of Shakespeare's Starlings • In the 1800s and early 1900s, introducing foreign species of animals and plants to North America was a popular, unregulated activity • In 1890, a group of Shakespeare enthusiasts released about 120 starlings in New York's Central Park • It was part of a project to bring to America every bird species mentioned in Shakespeare’s works

3. Their population is estimated at well over 100 million Current • Today, the starling range extends from Mexico to Alaska 1955 Current 1955 1945 1935 1925 1945 1905 1915 1925 1935 1925 1935

4. Starlings are omnivorous, aggressive, and tenacious • They cause destruction and often replace native bird species • Attempts to eradicate starlings have been unsuccessful • Over 5 million starlings have been counted in a single roost

5. The starling population in North America has some features in common with the global human population • Both are expanding and are virtually uncontrolled • Both are harming other species • Population ecology is concerned with changes in population size and the factors that regulate populations over time

6. 35.1 Populations are defined in several ways • Ecologists define a population as a single-species group of individuals that use common resources and are regulated by the same environmental factors • Individuals in a population have a high likelihood of interacting and breeding with one another • Researchers must define a population by geographic boundaries appropriate to the questions being asked

7. POPULATION STRUCTURE AND DYNAMICS 35.2 Density and dispersion patterns are important population variables • Population density is the number of individuals in a given area or volume • It is sometimes possible to count all the individuals in a population • More often, density is estimated by sampling

8. One useful sampling technique for estimating population density is the mark-recapture method Figure 35.2A

9. The dispersion pattern of a population refers to the way individuals are spaced within their area • Clumped • Uniform • Random

10. This is the most common dispersion pattern in nature • It often results from an unequal distribution of resources in the environment • Clumped dispersion is a pattern in which individuals are aggregated in patches Figure 35.2B

11. A uniform pattern of dispersion often results from interactions among individuals of a population • Territorial behavior and competition for water are examples of such interactions Figure 35.2C

12. Random dispersion is characterized by individuals in a population spaced in a patternless, unpredictable way • Example: clams living in a mudflat • Environmental conditions and social interactions make random dispersion rare

13. 35.3 Idealized models help us understand population growth • Idealized models describe two kinds of population growth • exponential growth • logistic growth

14. Exponential growth is the accelerating increase that occurs during a time when growth is unregulated • A J-shaped growth curve, described by the equation G = rN, is typical of exponential growth • G = the population growth rate • r = the intrinsic rate of increase, or an organism's maximum capacity to reproduce • N = the population size

15. Figure 35.3A

16. It tends to level off at carrying capacity • Carrying capacity is the maximum population size that an environment can support at a particular time with no degradation to the habitat • Logistic growth is slowed by population-limiting factors Figure 35.3B

17. K = carrying capacity • The term (K - N)/Kaccounts for the leveling off of the curve • The equation G = rN(K - N)/K describes a logistic growth curve Figure 35.3C

18. a population's growth rate will be low when the population size is either small or large • a population’s growth rate will be highest when the population is at an intermediate level relative to the carrying capacity • The logistic growth model predicts that

19. 35.4 Multiple factors may limit population growth • Increasing population density directly influences density-dependent rates • such as declining birth rate or increasing death rate • The regulation of growth in a natural population is determined by several factors • limited food supply • the buildup of toxic wastes • increased disease • predation

20. Field studies of the song sparrow have demonstrated that birth rates may decline as a limited food supply is divided among more and more individuals Figure 35.4A

21. Aphids show exponential growth in the spring and then rapidly die off when the climate becomes hot and dry in the summer • Abiotic factors may limit many natural populations Figure 35.4B

22. Density-dependent birth and death rates • Abiotic factors such as climate and disturbances • Populations often fluctuate in number • A natural population of song sparrows often grows rapidly and is then drastically reduced by severe winter weather • Most populations are probably regulated by a mixture of factors Figure 35.4C

23. 35.5 Some populations have "boom-and-bust" cycles • Some populations go through boom-and-bust cycles of growth and decline • Example: the population cycles of the lynx and the snowshoe hare • The lynx is one of the main predators of the snowshoe hare in the far northern forests of Canada and Alaska

24. About every 10 years, both hare and lynx populations have a rapid increase (a "boom") followed by a sharp decline (a "bust") Figure 35.5

25. Recent studies suggest that the 10-year cycles of the snowshoe hare are largely driven by excessive predation • But they are also influenced by fluctuations in the hare's food supply • Population cycles may also result from a time lag in the response of predators to rising prey numbers