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Environmental Science: Toward a Sustainable Future Richard T. Wright

Environmental Science: Toward a Sustainable Future Richard T. Wright. Chapter 4. Ecosystems: How They Change PPT by Clark E. Adams (modified). Factors That Contribute to Ecosystem Change. Dynamics of natural populations Mechanisms of population equilibrium Ecosystem response to disturbance.

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Environmental Science: Toward a Sustainable Future Richard T. Wright

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

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

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

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

  5. Population Growth Curves

  6. Population Growth Curves • Reproductive strategies: Not really- think insects, fish, frogs Many offspring with low parental care Maybe, maybe not Few offspring with high parental care J-shaped growth curve S-shaped growth curve R strategists K strategists

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

  8. Biotic Potential and Environmental Resistance

  9. 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

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

  11. Predator–Prey Balance: Wolves and Moose

  12. 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. • Predators reduce the herbivore population; it is maintained so that overgrazing or other overuse does not occur.

  13. 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

  14. 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?

  15. 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/

  16. Competition- an overview • Interspecific competition- different species compete for the same resource- my tomatoes and sheep sorel in my garden! • It is often less of a problem because or specific habitats and niches, until an invader appears- zebra mussel, ruffe, etc. • Intraspecific competition- competition within a species- songbirds sing mainly to warn other songbirds to stay out!

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

  18. 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

  19. Primary Succession

  20. 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.

  21. Secondary Succession

  22. Aquatic Succession

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

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

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

  26. Ground Fire

  27. 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?

  28. Resilience in Ecosystems

  29. 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

  30. What you should know from Ch. 4Population growth curves- J vs SBiotic potentialEnvironmental ResistanceDensity dependent and independent resistance factorsK vs R strategistsKeystone speciesInter & intraspecific competitionSuccession- primary & secondaryDisturbance and resilience

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