Tuesday, May 21, 2013

The away-field advantage

Few species reside solely in the location where they originated. In fact, the migration of species is a predominant feature of life on Earth. Species expand, contract and shift their geographical distributions constantly. It is our perception of these ecosystems and the boundaries in time and space that we draw around them that makes us discriminate between native and non-native species - a fully arbitrary process. Nevertheless, we have become very concerned about recent species invasions mainly because of the tremendous damage some non-native species can cause to ecological systems, our health, and our economy.

Although many species have been introduced outside of their home ranges, relatively few introduced species become abundant and widespread in the new ranges. Identifying the mechanisms driving profound invasions when they do occur is the focus of a large body of research in invasion biology. It has long been assumed the worst invasive species have an "away-field advantage." meaning they succeed because they do better in their new territories than they do at home. They escape their natural enemies, use novel weapons and defense mechanisms on unsuspecting  natives and generally outcompete local flora and fauna by disrupting the balance of the existing ecosystem.

Now a new study led by the Smithsonian Environmental Research Center reveals that this fundamental assumption is not nearly as common as we might think. To determine whether individuals of invasive introduced species are generally larger, more fecund, or more abundant in their novel ranges, the researchers quantitatively evaluated population data from both the native and introduced range for 53 introduced species that are considered to be invasive, including 36 species categorized as among the “World's Worst Invasive Alien Species” a list assembled within the Global Invasive Species Database

Although their data generally support the idea that invasive species exhibit increased performance in their introduced range, roughly half of the species investigated performed similarly between the home and away ranges. One implication of this finding is that novel ecological and evolutionary conditions in the introduced range may only partly explain success in a new range. Indeed, there has been much recent progress in determining the traits that make some species invasive across a range of environmental conditions, with growing evidence that many successful introduced species share similar traits with successful native species. The authors conclude that species' traits, and particularly the interaction between traits and environmental context, may be a better predictor of invasion success than novel conditions alone.

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