1. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 5: Population Ecology

2. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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 The Spread of Shakespeare's Starlings

3. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Today, the starling range extends from Mexico to Alaska Their population is estimated at well over 100 million Current 1955 1945 1935 1925 1935 1915 1905 1925 1935 1945 1955 Current

4. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Over 5 million starlings have been counted in a single roost Starlings are omnivorous, aggressive, and tenacious They cause destruction and often replace native bird species Attempts to eradicate starlings have been unsuccessful

5. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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 35.1 Populations are defined in several ways

7. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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 35.2 Density and dispersion patterns are important population variables POPULATION STRUCTURE AND DYNAMICS

8. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings One useful sampling technique for estimating population density is the mark-recapture method Figure 35.2A

9. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The dispersion pattern of a population refers to the way individuals are spaced within their area –Clumped –Uniform –Random

10. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Clumped dispersion is a pattern in which individuals are aggregated in patches –This is the most common dispersion pattern in nature –It often results from an unequal distribution of resources in the environment Figure 35.2B

11. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Idealized models describe two kinds of population growth –exponential growth –logistic growth 35.3 Idealized models help us understand population growth

14. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 35.3A Example of Exponential Growth Describes the rate of expansion of a population under ideal, unregulated conditions.

15. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Logistic growth is slowed by population- limiting factors –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 Figure 35.3B

16. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings How carrying capacity plays a role in exponential growth and logistic growth:

17. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The logistic growth model predicts that –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

18. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Density-dependent limiting factor- a factor that causes population growth to decreases a result of the population size –Competition –Predation –Parasitism –Disease 35.4 Multiple factors may limit population growth

19. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Density-independent limiting factors- affect all populations in similar ways, regardless of the population size –Weather –Natural Disasters –Seasonal Cycles –Human Activities Damming rivers Clear-cutting forests DEVELOPMENT

20. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Abiotic factors may limit many natural populations –Aphids show exponential growth in the spring and then rapidly die off when the climate becomes hot and dry in the summer Figure 35.4B

21. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Most populations are probably regulated by a mixture of factors –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 Figure 35.4C

22. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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 35.5 Some populations have "boom-and-bust" cycles

23. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –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

24. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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

25. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The human population as a whole has doubled three times in the last three centuries The human population now stands at about 6.7 billion and may reach 9.3 billion by the year 2050 Current ClockCurrent Clock Most of the increase is due to improved health and technology –These have affected death rates 35.8 Connection: The human population has been growing exponentially for centuries THE HUMAN POPULATION

26. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings How to Calculate Growth Rates:  Four influences:  Birth rate   Death rate   Immigration   Emigration   Birth + Immigration – Death – Emigration = Population Count

27. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The history of human population growth Figure 35.8A

28. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The ecological footprint represents the amount of productive land needed to support a nation’s resource needs The ecological capacity of the world may already be smaller than its ecological footprint http://www.myfootprint.org/

29. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Ecological footprint in relation to ecological capacity Figure 35.8B

30. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The exponential growth of the human population is probably the greatest crisis ever faced by life on Earth Figure 35.8C

31. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Population stability is achieved when there is zero population growth –Zero population growth is when birth rates equal death rates 35.9 Birth and death rates and age structure affect population growth

32. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The demographic transition is the shift from high birth and death rates to low birth and death rates –During this transition, populations may grow rapidly until birth rates decline Figure 35.9A

33. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The age structure of a population is the proportion of individuals in different age- groups –Age structure affects population growth

34. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 35.9B RAPID GROWTH Kenya MaleFemale Percent of population SLOW GROWTH United States MaleFemale ZERO GROWTH/DECREASE Italy MaleFemale Ages 45+ Ages 15–44 Under 15 Ages 45+ Ages 15–44

35. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Age-structure diagrams not only reveal a population's growth trends –They also indicate social conditions Increasing the status and education of women may help to reduce family size