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Flow of Energy

Introduces diagrams that show how energy decreases from lower to higher trophic levels.

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The zebra mussel (Dreissena polymorpha) is one of the best known and most successful invasive species


Invasive Species

Why It Matters

Where'd You Come From?

Invasive species are well known for the changes they cause in ecosystems. A few dramatic cases like the Cane Toad (Bufo marinus) in Australia or the Brown Tree Snake (Boiga irregularis) in Guam have greatly influenced people's opinion of invasive species, creating images of marauding invasive species callously driving native species to extinction. However, the real story is a bit different. Every day up to 10,000 species are transported around the world into new ecosystems. Think about this for a second, 10,000 species per day. Have you heard of 10,000 invasive species? No, the truth is that ecosystems are both complex and resilient. Most species transported into ecosystems can't compete with the natives who grew up in that ecosystem. Natural selection gives the native species an edge. Make no mistake, there are exceptions, and their effects both ecologically and economically can be devastating, but they are the exception and not the rule. For a species to be a successful invader it needs to have an edge, like a chemical defense or life history trait which is unknown in the system it invades and allows it to dominate. Find out more about some species which have these traits, and what researchers are learning about them.

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Use the resources below to answer the following questions:

  1. What is the difference between an exotic and native species?
  2. What key trait of zebra mussels (Dreissena polymorpha) has given them a competitive edge over native mussels in the Great Lakes?
  3. Have zebra mussels caused the extinction of native mussels? Have all the effects of zebra mussels been negative? How does this affect your view of invasive species?
  4. How does the rate of movement and spacial scale currently seen with invasive species differ from simple range expansion of species? How does the rate of change affect a native species' ability to respond to a new competitor or predator?
  5. How has international shipping affected the spread of species? Explain your answer as fully as you can. What steps would you take to control this situation?
  6. How does the invasion of the Rusty Crayfish (Orconectes rusticus) into Sparkling Lake demonstrate that extinction is not the only or even the most common outcome of invasive species?

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