1. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Species Interactions Food chains and food webs describe which species eat which other species. These feeding levels—called trophic levels—include producers and consumers.

2. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Species Interactions Other types of species interactions include: Competition—species compete when their niches overlap. Symbiosis—species may live in close association with one another. A symbiotic relationship may involve parasitism, commensalism, or mutualism.

3. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Science and Society: Invasive Species Invasive species are species that are introduced from their native habitat into a new habitat and that proceed to thrive there. This results in harm to native species. Invasive species: Usually are unintentionally introduced (at least these days) May out-compete or devour native species

4. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Kinds of Ecosystems There are terrestrial and aquatic ecosystems. Terrestrial ecosystems are called biomes.biomes

5. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Energy Flow in Ecosystems All organisms need energy in order to grow, reproduce, and perform the activities necessary for survival. The amount of organic matter in an ecosystem is its biomass. The rate at which an ecosystem’s producers build biomass is the ecosystem’s primary productivity.

6. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Energy Flow in Ecosystems On average, only about 10 percent of the energy at one trophic level becomes available to the next level. The other 90 percent is: Uneaten organisms Heat lost to the environment Feces Maintenance

7. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Integrated Science: Energy Leaks Where Trophic Levels Meet Moving energy from one trophic level to another involves a long series of chemical reactions. Because every chemical reaction involves some energy loss to the environment, we see why so much energy leaks from one trophic level to the next.

8. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Kinds of Ecosystems Aquatic ecosystems include freshwater and saltwater environments as well as estuaries where freshwater and saltwater meet.

9. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Integrated Science: Materials Cycling Many substances on Earth travel through a continuous cycle from living organisms to the abiotic environment and back—these are biogeochemical cycles. Three of these cycles involve water, carbon, and nitrogen.

10. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Integrated Science: Materials Cycling The water cycle: Water evaporates from the oceans into the atmosphere. Water is moved around the atmosphere by winds. Water precipitates as rain or snow over ocean or land. Water moves into the biotic world when it is absorbed or swallowed by organisms. Some of this water then passes up the food chain. The rest is returned to the abiotic environment in a variety of ways, including through animal respiration, perspiration, excretion, and elimination, and evaporation from plant tissue.

11. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Integrated Science: Materials Cycling The carbon cycle: Most of the inorganic carbon on earth exists as carbon dioxide and is found either in the atmosphere or dissolved in ocean waters. Plants and other producers convert carbon dioxide to glucose during photosynthesis. Carbon is returned to the environment by living organisms as carbon dioxide, a product of cellular respiration. Because atmospheric carbon dioxide traps heat on the planet, this has resulted in global warming.

12. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Integrated Science: Materials Cycling The nitrogen cycle: Nitrogen is found primarily as nitrogen gas, the dominant component of the Earth’s atmosphere. In order for living organisms to make use of nitrogen, it has to be converted into usable form. Living organisms rely on bacteria to accomplish this transformation. Nitrogen is converted to ammonium by nitrogen-fixing bacteria in soil, and then to nitrates by nitrifying bacteria. Nitrogen returns to the abiotic environment when it is converted back to nitrogen gas by denitrifying bacteria.

13. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Change in an Ecosystem Ecological succession describes how the species composition of an ecosystem changes after a disturbance. Ecological succession is sometimes divided into two types, primary succession and secondary succession.

14. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Change in an Ecosystem Primary succession: the colonization of bare land devoid of soil; may occur when new land is formed by volcanic activity or when a glacier’s retreat reveals bare rock. Early colonizers of new habitat, known as pioneer species, must survive with few nutrients and little existing organic matter, cope with direct sunlight, and survive the variable temperatures that result from lack of cover. Pioneer species are often succeeded by grasses, shrubs, and finally, trees. Ecological succession culminates in a climax community. During the process of succession, the total biomass of the ecosystem typically increases, as does the number of species.

15. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Change in an Ecosystem

16. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Change in an Ecosystem Secondary succession occurs when a disturbance destroys existing life in a habitat, but leaves soil intact. Examples: fires, abandonment of old farmland Because soil is already present, secondary succession proceeds more quickly than does primary succession.

17. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Population Studies

18. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Population Studies Population size over time depends on four variables—birth rate, death rate, the rate of immigration into the population, and the rate of emigration out of the population.

19. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Population Studies Exponential growth occurs when a population grows at a rate that is proportional to its size.

20. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Population Studies Logistic growth occurs when population growth slows as it reaches the habitat’s carrying capacity, the maximum number of individuals or maximum population density the habitat can support.

21. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Population Studies Organisms have different life history strategies. r-selected organisms produce a lot of offspring and invest little in each offspring. For example, they provide little parental care. Few of the offspring reach adulthood. K-selected organisms produce a few offspring and provide a great deal of investment in each. For example, they provide a lot of parental care. Most of their offspring reach adulthood. Of course, these are two extremes along a continuum.

22. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Population Studies

23. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Human Population Growth Human population is currently about 6.5 billion. Although world population continues to grow rapidly, the rate of growth has slowed, so that growth is no longer exponential. Scientists now believe that if present trends continue, the global human population will peak at around 10 billion soon after 2050.

24. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Human Population Growth Some human populations have undergone a demographic transition, a shift from high birth and death rates to low birth and death rates. Usually, death rate decreases first, due to medical and public health advances. Later, birth rate also declines. During the period between the fall in death rate and the fall in birth rate, the combination of low death rate and high birth rate causes the population to grow very rapidly.

25. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Human Population Growth A pyramid-shaped age structure diagram, such as that of Kenya, is a sign of a rapidly growing population. Most of the population is young and therefore at or approaching reproductive age. The United States has an age structure that is much more even—its population is growing slowly. In Italy, much of the population is older, and there are relatively few children. Italy’s population is stable or even declining.

26. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Human Population Growth