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Oecologia

Title:		Mutualism in a community context: the positive feedback between an ant-aphid mutualism and a gall-making midge
Author(s):		Savage AM; Peterson MA;
Address:		"Department of Biology, Western Washington University, Bellingham, WA, USA. savage@rice.edu"
Journal Title:		Oecologia
Year:		2007
Volume:		20061116
Issue:		2
Page Number:		280 - 291
DOI:		10.1007/s00442-006-0582-1
ISSN/ISBN:		0029-8549 (Print) 0029-8549 (Linking)
Abstract:		"Although mutualisms are widespread and often described in natural history accounts, their ecological influences on other community members remain largely unexplored. Many of these influences are likely a result of indirect effects. In this field study, we investigated the indirect effects of an ant-aphid mutualism on the abundance, survival rates and parasitism rates of a co-occurring herbivore. Rabdophaga salicisbrassicoides (Diptera: Cecidomyiidae) induces rosette galls on the developing shoots of Salix exigua trees, and populations can reach outbreak densities (up to 1,000 galls/stem) in central Washington State (USA). Ant-tended aphids feed on these same stems and often feed on gall tissue. In this study we used a combination of manipulative experiments and observational surveys to test the hypothesis that the abundances of aphids, ants, and galls have positive and reciprocal effects on one another, in a manner that would create a positive feedback loop in population growth. In addition, we examined whether the combined presence of ants and aphids reduces parasitism rates for the gallers. In support of the positive feedback loop hypothesis, aphids enjoyed higher population growth rates in the presence of ants and galls, the presence of ants and aphids resulted in increased abundance of galls, and the abundances of ants, aphids and galls were all positively correlated with one another. However, the mechanism underlying the positive effect of ants and aphids on galler density remains unknown, as the mutualism did not affect parasitism rates. More broadly, this study demonstrates that mutualisms can have significant and complex indirect effects on community and population ecology"
Keywords:		Analysis of Variance Animals Ants/*physiology Aphids/*physiology Diptera/*physiology Population Dynamics Salix/*parasitology *Symbiosis Washington;
Notes:		"MedlineSavage, Amy M Peterson, Merrill A eng Comparative Study Research Support, Non-U.S. Gov't Germany 2006/11/16 Oecologia. 2007 Mar; 151(2):280-91. doi: 10.1007/s00442-006-0582-1. Epub 2006 Nov 16"