Keystone Species and Trophic Cascades

Description:

This activity explores the content and research discussed in the film Some Animals are More Equal than Others, which tells the story of the ecologists who first documented the role of keystone species in ecosystem regulation.

The short film explores the work of ecologists Robert Paine and James Estes. Robert Paine’s experiments showed that removing starfish from tidal pools has a big impact on the population sizes of other species. James Estes and colleagues discovered that the kelp forest ecosystems of the North Pacific are regulated by the presence or absence of sea otters, which feed on sea urchins that consume kelp. These direct and indirect effects of starfish, sea otters, and other so-called keystone species describe a phenomenon known as a trophic cascade. These early studies were the inspiration for hundreds of subsequent investigations on how population sizes are regulated in a wide variety of ecosystems.

You will use evidence to explain why some species play the role of a keystone species in their ecosystem, and you will explain the concept of a trophic cascade using examples from different ecosystems