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Cascading trait-mediation: disruption of a trait-mediated mutualism by parasite-induced behavioral modification


H. Liere, Dept of Ecology and Evolutionary Biology, Univ. of Michigan, 830 N. University, Ann Arbor, MI 48109, USA. E-mail:


Trait-mediated indirect interactions (TMII) are important driving-forces causing trophic cascades in aquatic and terrestrial food webs. Furthermore, since most biological communities are not simple food chains but complex networks of interactions, one TMII within a community might easily be influenced by another TMII. In other words, TMII themselves can be cascades with potential implications for community dynamics. Here we report on one of such cascade, where a parasitic fly induces behavioral changes that disrupt a trait-mediated ant–hemipteran mutualism. We show that during parasite-induced low-activity periods, the ant Azteca instabilis fails to protect its mutualistic scale-insect partner against predatory ladybeetles. Thus, in the presence of the parasite, ladybeetles ate as many scales in ant-patrolled plants as they did in ant-free plants. These results demonstrate how, through a cascade of trait-mediated interactions, associations between members of a community can be drastically altered.