Wetting One's Appetite

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Science  19 Jun 2009:
Vol. 324, Issue 5934, pp. 1493
DOI: 10.1126/science.324_1493a

Ecological studies of food webs and their resources tend to focus on the limited availability of and competition for nutrients and energy. In some systems, however, water may exert an important influence on species interactions. McCluney and Sabo have investigated the impact of distinct water regimes on ecological systems in the San Pedro River in southern Arizona. In a field setting, they furnished cages containing field crickets with an ample supply of cottonwood and willow leaves, and they varied two factors: the presence/absence of wolf spiders (which prey on crickets) and mesic/xeric conditions. They found that when water was scarce, crickets consumed significantly more green leaves, rather than old litter, and experienced significantly higher mortality, presumably due to wolf spider predation, in comparison to cages lacking spiders. In contrast, in cases of rainfall or when water was provided, the cricket-spider interaction strength diminished almost to zero, suggesting that crickets were more important as a source of water than as nutrient. These data indicate that in some ecosystems, interactions between species can differ depending on water availability, and thus the local effects of global climate change—including derived aridification, droughts, and increases in precipitation—may alter food webs significantly.

Ecology 90, 1463 (2009).

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