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American Association for the Advancement of Science

Whales and butterflies: The migration effect

Loggerhead turtles are highly migratory throughout their range with individuals known to cross both the Atlantic and Pacific Oceans. The individual here has been equipped with a satellite tag in Greece to follow its post-breeding migration.
[ Gail Schofield]

What do a 40-ton whale and near-weightless butterfly have in common? They both migrate every year, along with billions of other animals like ducks, turtles and moths. Now, a new study in the 4 April issue of the journal Science explains how important migration is to shaping ecosystems on Earth.

The role of migratory species those that move from one place to another seasonally is more important than many have thought, emphasize the authors in this Review in Science. When animals migrate, they carry nutrients, energy and even other organisms across long distances. Birds fly from Europe to Africa, for example. And loggerhead turtles cross both the Atlantic and Pacific Oceans.

Their migration activities can alter ecological networks in surprising ways, changing food web structures, for example, or introducing toxins, carried on the backs of seabirds. They may even change the physical properties of a water body, as salmon do, increasing air-water gas exchange in the streams and lakes to which they return to lay eggs.

But while research has focused on how animals migrate, at what point in a season they do, and to where, migration's effect on local ecology networks has not received much attention. Indeed, it has been under-studied and is therefore under-appreciated say the Swiss Ornithological Institute's S. Bauer and the University of Colorado's B. J. Hoye.

This is important, they suggest, particularly as migration is seasonal, and thus very easy to predict (every winter, ducks will fly south, for example). This predictability makes understanding migration a powerful way to understand the many different species and ecosystems on Earth.

S. Bauer and B. J. Hoye review several studies that have shown the many ways that migratory species change the communities through which they travel. They argue that scientists studying how animals and plants in a community affect each other should not forget to consider animal migration. The scientists even provide a new framework that will help scientists do this.