ECOLOGY/EVOLUTION

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Science  11 Apr 2003:
Vol. 300, Issue 5617, pp. 217
DOI: 10.1126/science.300.5617.217a

Although ecological systems, almost by definition, consist of complex webs and chains of interactions among multiple species, it is not necessarily simple to document and quantify these interactions. Bailey and Whitham investigated a system involving four very different groups of organisms—mammals, trees, arthropods, and birds—in Arizona. The patterns of insectivorous bird predation were altered by elk browsing on aspen trees, because the consumption of aspen shoots by elk reduced the quantities of galls produced by sawflies, the presence of which had significant and positive effects on the species richness and abundance of other arthropod species. These results, achieved by a combination of observation and experiments in which elk were excluded and browsing was simulated, show how the system is governed by a combination of top-down and bottom-up effects, and how the indirect manipulation of one species (sawfly) by another (elk) can have effects that ramify throughout the community.—AMS

OIKOS101, 127 (2003).

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