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Keystone Species and Ecological Release

Keystone Species and Ecological Release. Keystone Species. Some species play such pivotal roles in their ecosystems that we call them keystone species. These are species whose presence or absence governs the existence and overall composition of the system. What Are Keystone Species?.

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Keystone Species and Ecological Release

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  1. Keystone Species and Ecological Release

  2. Keystone Species Some species play such pivotal roles in their ecosystems that we call them keystone species These are species whose presence or absence governsthe existence and overall composition of the system

  3. What Are Keystone Species? • A keystone species holds a community together, when it disappears, so does the biological community. Elimination of a keystone species dramatically alters the structure and function of an ecosystem.

  4. American Alligator – a Keystone Species • Largest North American reptile; humans are their only predator. • Hunted nearly to extinction for exotic meat, and leather to make shoes and pocketbooks, and for sport.

  5. Ecological Niche of American Alligator • Gators dig holes that collect freshwater during the dry season which serve as refuges for aquatic life, and supply freshwater and food for many animals.

  6. Ecological Niche of American Alligator • Alligator nesting mounds serve as nesting and feeding sites for herons and egrets

  7. Ecological Niche of American Alligator • Alligator eat large numbers of predatory gar fish and help maintain healthy numbers of game fish such as bass and bream.

  8. Ecological Niche of American Alligator • As alligators move from gator holes to nesting sites, they keep areas of open water free of invading vegetation. This helps to maintain healthy ecosystems with flowing water.

  9. American Alligator Protection • In 1967, the US Government placed the American alligator on the Endangered Species List, which protected it from hunting. • By 1975, the American alligator populations rebounded successfully.

  10. E.O. Wilson • “The loss of a keystone species is like a backhoe accidentally striking a power line. It causes lights to go out all over”

  11. Keystone Species and Ecological Release When a keystone species is removed from an ecosystem, prey species often undergo an ecological release A population explosion that occurs when a keystone predator or competitor is removed from a system

  12. Keystone Species and Ecological Release When populations of California sea otters declined in the mid-20th century populations of sea urchins increased explosively

  13. Keystone Species and Ecological Release With the sea otters gone, populations of sea urchins increased explosively

  14. Keystone Species and Ecological Release Soon, millions of sea urchins began to graze on the kelp making up the off-shore kelp beds Soon, California’s kelp bed ecosystems-- and all the species they contained --began to disappear

  15. Keystone Species and Ecological Release Which organisms turned out to be the “keystones” that governed this ecosystem? the sea-otters ( Enhydra lutis ) Which organisms underwent ecological release? the sea-urchins

  16. Ecological Release Another example: When ranchers killed coyotes, jackrabbit populations underwent a population explosion

  17. Ecological Release Soon farms and vegetable gardens were over-run with jackrabbits

  18. and Jackalopes, too

  19. But Coyotes can not control the larger Jackalopes, wolves are needed for that.

  20. Which organisms were the keystones in this example? the coyotes Which organisms underwent ecological release? the jackrabbits

  21. Ecological Release Duringthe mid-1900s, fleets of whale ships decimated the world’s populations of baleen whales driving several whale species to near-extinction

  22. Ecological Release Soon, populations of tiny, shrimp-like organisms calledkrill underwent a population explosion Can you guess why? Baleen whales eat krill. Which organisms underwent ecological release? the krill

  23. We have just seenthree examples of ecological release involving jackrabbits,krill, and sea urchins In each case, a population explosion resulted when a local population was released fromthe pressures of a key predator or competitor

  24. Can you think of a population that has undergone Ecological Release here in North Idaho? Can you guess what might be some keystone species in north Idaho?

  25. Ecological Release Our own population has grown explosively in the past 150 years We ourselves may be undergoing an ecological release. Why? Science and medicine have helped us conquer the germs that once held our numbers in check.

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