Free response · Unit 8 Beta

Remove a keystone predator: sea otters and kelp forests

Conceptual Analysis · 4 points

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The question

Name: ______________________   Date: ____________   Remove a keystone predator: sea otters and kelp forests (4 points)

Model

Part of a kelp forest food web

Along rocky Pacific coasts, giant kelp (a large brown alga) grows in underwater forests. Sea urchins graze on kelp, and sea otters eat sea urchins. Many fish species shelter, feed and lay eggs among the kelp. In the 1990s, the sea otter population of one island chain fell by about 90% within a decade; the leading explanation is that killer whales there began eating far more otters than before.

Kelp forest food webArrows point from food to eater. Kelp is eaten by sea urchins. Sea urchins are eaten by sea otters. Sea otters are eaten by killer whales. A dashed arrow shows that kelp provides shelter and food for kelp-forest fish.Killer whalesSea ottersSea urchinsGiant kelpKelp-forest fishshelter, egg-laying sites, foodArrows point from food to eater.

  1. (a) Sea otters are a keystone species in this community. Describe what makes a species a keystone species. [1 point]

  2. (b) Explain how the decline in sea otters is likely to affect the amount of kelp. [1 point]

  3. (c) Predict how the number of kelp-forest fish species will change over the next decade, and justify your prediction. [1 point]

  4. (d) An ecologist claims that a decline of 90% in one species of kelp-forest fish would change the community much less than the 90% decline in sea otters did. Justify this claim. [1 point]