Environmental Science: Toward a Sustainable Future Richard T. Wright

1. Environmental Science: Toward a Sustainable Future Richard T. Wright Chapter 4 Ecosystems: How They Change PPT byClark E. Adams

2. Factors That Contribute to Ecosystem Change • Dynamics of natural populations • Mechanisms of population equilibrium • Mechanisms of species adaptation • Ecosystem response to disturbance • Lessons to learn

3. Dynamics of Natural Populations • Population growth curves • Biotic potential versus environmental resistance • Density dependence and critical number

4. Biotic Potential and Environmental Resistance

5. Population Equilibrium Births A dynamic balance between births and deaths. Deaths

6. Population Growth Curves

7. Population Growth Curves • Reproductive strategies: Many offspring with low parental care Few offspring with high parental care J-shaped growth curve S-shaped growth curve

8. Population Dynamics • Environmental resistance: combination of biotic and abiotic factors that may limit population increase • Predators, competitors, disease • Adverse weather, limited food/nutrients

9. Biotic Potential and Environmental Resistance

10. Density Dependence and Critical Numbers • Factors of environmental resistance are either: • density-independent: effect does not vary with population density; e.g., adverse weather • density-dependent: effect varies with population density; e.g., infectious disease • Critical number: the lowest population level for survival and recovery

11. Mechanisms of Population Equilibrium • Predator–prey dynamics • Competition • Interspecific • Intraspecific • Introduced species

12. Predator–Prey Balance: Wolves and Moose

13. Lessons to Be Learned about Predator–Prey Balance • Absence of natural enemies allows a herbivore population to exceed carrying capacity, which results in overgrazing of the habitat. • The herbivore population subsequently crashes. • The size of the herbivore population is maintained so that overgrazing or other overuse does not occur.

14. Plant–Herbivore Dynamics Reindeer on St. Matthew Island • No regulatory control (predation) on herbivores • Went into exponential growth pattern • Overgrazed habitat • Massive die-off of herbivores

15. Mechanisms of Population Equilibrium: Plant–Herbivore • Compare the predator–prey with plant–herbivore methods of controlling the size of the herbivore population. • How would the herbivore population growth curve look if diseases or predators were used as the control mechanism?

16. Keystone Species • A single species that maintains biotic structure of the ecosystem • Pisaster ochraceus: a starfish that feeds on mussels, keeping them from blanketing the rocks http://www.marine.gov/

17. Competition: Intraspecific • Territoriality: defense of a resource against individuals of the same species • Examples of wolves and songbirds • Results in priority access and use of resources • How do wolves and songbirds establish territory?

18. Competition: Interspecific • Grasslands contain plants with both fibrous roots and taproots • Coexist by accessing resources from different soil levels

19. Introduced Species • Rabbits in Australia (next slide) • Chestnut blight in United States • Japanese beetles, fire ants, gypsy moths in United States • Water hyacinth, kudzu, spotted knapweed, purple loosestrife (see Fig. 4-13 in text) in United States

20. Rabbits Overgrazing in Australia

21. Introduced Species • Why have introductions of nonnative and exotic species resulted in a degradation of ecosystems? (Think in terms of environmental resistance and biotic potential.) • An example of the answer to this question is given in the next slide.

22. Introduced Species: Rabbits in Australia • Introduced into Australia from England in 1859 • No natural enemies – rabbit population exploded • Overabundant herbivore population devastated natural vegetation (see Fig. 4-11 in text). • Using disease as control measure – why will this procedure fail in the long term?

23. Mechanisms of Species Adaptation • Change through natural selection • Selective pressure determines which organisms survive and reproduce and which are eliminated.

24. ENVIRONMENT GENES + ADAPTATIONS NATURALSELECTION: For? or Against? Recipe for Change

25. Adaptations to the Environment

26. The Limits of Change • Adapt • Move (migrate) • Die (extinction)

27. Vulnerability of different organisms to environmental changes

28. Prerequisites for Speciation • Original population must separate into smaller populations that do not interbreed with one another. • List some ways this might happen. • Separated populations must be exposed to different selective pressures. • Example: arctic and gray fox (next slide)

29. Speciation: Foxes

30. Speciation: Galápagos Finches

31. Ecosystem Responses to Disturbance • Ecological succession • Disturbance and resilience • Evolving ecosystems

32. Equilibrium Theory • Ecosystems are stable environments in which the biotic interactions among species determine the structure of the communities present.

33. Succession and Disturbance • Ecological succession: transition between biotic communities • Primary: no previous biotic community • Secondary: previously occupied by a community • Aquatic: transition from pond or lake to terrestrial community

34. Primary Succession

35. Primary Succession • Mosses invade an area and provide a place for soil to accumulate. • Larger plants germinate in the new soil layer, resulting in additional soil formation. • Eventually shrubs and trees will invade the area.

36. Secondary Succession

37. Aquatic Succession

38. Disturbance and Resilience • Removes organisms • Reduces populations • Creates opportunities for other species to colonize

39. Fire and Succession http://www.fs.fed.us/photovideo/

40. Ground Fire

41. Fire and Succession • Fire climax ecosystems: dependent upon fire for maintenance of existing balance; e.g., grasslands, pine and redwood forests • What significance does this have for humans and where they live?

42. Resilience in Ecosystems

43. Nutrient release to soil Regrowth by remnant roots and seeds Invasions from neighboring ecosystems Rapid restoration of energy flow and nutrient cycling Resilience Mechanisms after a Forest Fire

44. Lessons to Learn • Managing ecosystems • The pressure of population

45. Managing Ecosystems • Protecting and managing the natural environment to maintain the goods and services vital to human economy and survival.

46. The Pressures of Population • What is the carrying capacity for the human population on Earth? • How will the human ecological footprint impact on nature’s goods and services?

47. Carrying Capacity and Overshoot

48. End of Chapter 4