Invading Trout Reduce Forest Spiders by Altering the Stream Food Web That Supplies Their Prey
A team of researchers from the U.S. and Japan have shown that exotic species can have strong effects that degrade not only the ecosystems they invade, but also spread to adjacent ecosystems as well. Colden Baxter, Kurt Fausch and Phillip Chapman from Colorado State University collaborated with Masashi Murakami of Hokkaido University to conduct a large experiment in a watershed of northern Japan. The study showed that non-native rainbow trout usurped forest insects that fell into the stream, depriving native trout of more than 80% of their diet. This forced the native fish to feed primarily on insect larvae that live on the stream bottom, which decreased adult insects emerging from the stream to the forest. In turn, this caused a 65% reduction in forest spiders that, like other forest-dwellers such as birds and bats, prey on insects emerging from the stream. This research demonstrates that species invasions can decouple critical connections between ecosystems like streams and forests and have strong effects that propagate across their boundaries to generate ecological surprises.
The Matrix Enhances the Effectiveness of Corridors and Stepping Stones
Human-modified landscapes have been implicated worldwide as a primary cause for the loss of native flora and fauna. Corridors and stepping stones have been proposed as strategies to increase landscape connectivity for fragmented populations. However, animals also move through the matrix, or habitat between patches, and the influence of different matrix types on the effectiveness of corridors and stepping stones has never been evaluated experimentally. Researchers from Louisiana State University, Kristen Baum, Kyle Haynes, Forrest Dillemuth and James Cronin, investigated the influence of the matrix on the effectiveness of corridors and stepping stones for the dispersal of planthoppers in experimental landscapes in northeast North Dakota. The scientists found that the matrix can determine whether, and to what extent, corridors and stepping stones increase landscape connectivity. Corridors were more effective in a low resistance matrix (one that facilitates high rates of dispersal among patches) than a high-resistance matrix (one that promotes low rates of dispersal among patches), while stepping stones only increased planthopper colonization when surrounded by a low-resistance matrix. According to the authors, conservation strategies and management plans should explicitly consider the matrix when evaluating strategies to increase landscape connectivity.
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