A small change that negatively affects one species will have drastic influence upon that species' entire ecosystem. It may be that only species that are very opportunistic under unfavorable conditions end up thriving in the new world climate. Some researchers stress the importance of determining keystone species within an ecosystem, or species that have key roles in the behavior of an ecosystem. The logic behind this is that if the keystone species are able to survive climate change, then the ecosystem has a better chance of succeeding as well. An example of this is the sea otter.
Sea otters feed on sea urchins, which in turn feed on kelp.
If the sea otter is removed from the ecosystem, the urchins grow out of control, destroying the kelp forests and thus destroying the entire ecosystem. More and more often, studies are showing that there are more keystone species in ecosystems than previously thought. The theory that keystone species will be important in the face of global warming may not hold much truth, however, if other species in an a ecosystem are not able to migrate to new climate as efficiently as the keystone species, thus taking away the importance of the keystone. There are many natural and man-made barriers that exist that could prevent certain species from migrating to new climate and cause this effect. One of these, of course, is the speed necessary for migration.