Ecologists recently have begun to consider how plasticity affects indirect interactions in multi-species assemblages. Previously, investigators interested in indirect interactions primarily focused on the indirect effects of prey consumption. However, plasticity also can generate indirect interactions, called trait-mediated indirect interactions (TMII) that affect the community. Although our understanding of how trophic interactions affect community composition has focused on density-mediated indirect interactions (DMII), such trait-mediated indirect interactions (TMII) recently have been shown to have an equal or greater community-wide effect than DMII.
Laboratory experiments revealed that predatory seastars and whelks altered the behavior of all of the many species of snails living on rocky shores in our area, and that these behavioral responses (e.g., reduced foraging, habitat shift) affected the amount of algae consumed, whereas three species of nonpredatory seastars did not. Interestingly, adult snails were not vulnerable to small species of predatory seastars, and yet they still responded to them. These results are of particular interest because they suggest that either behavioral responses in young snails might carry over to adults or that snails are vulnerable to a related species of seastar and unable to discriminate between them, necessitating further tests with an even greater taxonomic diversity of seastars. Predator identity and alarm signaling was found to elicit varying degrees of escape response, and antipredator cues were only briefly effective at high concentrations in standing water, raising doubt about the importance of TMII along wave swept rocky shores.
Field experiments yielded mixed results regarding the importance of TMIIs. Short-term experiments in tidepools revealed an immediate flight response by snails in response to predatory seastars and a decline in species richness and diversity of mobile invertebrates over six-months. However, no change was seen in species richness or diversity of algae due to a previously unrecognized density effect that can result in an overestimation of the strength of TMIIs. In contrast, seastar and whelk predators primarily affected boulder field communities via TMII rather than DMII in the two-year experiment conducted in boulder fields, although TMIIs were context dependent (depending on disturbance and exposure to physical conditions). Our experiments are enabling us to contrast the effects these short-term behavioral responses on rocky shore communities with that of longer-term morphological responses.
Steven Morgan, Ph.D.
Ecologists recently have begun to consider how plasticity affects indirect interactions in multi-species assemblages. Previously, investigators interested in indirect interactions primarily focused on the indirect effects of prey consumption. However, plasticity also can generate indirect interactions, called trait-mediated indirect interactions (TMII) that affect the community. Although our understanding of how trophic interactions affect community composition has focused on density-mediated indirect interactions (DMII), such trait-mediated indirect interactions (TMII) recently have been shown to have an equal or greater community-wide effect than DMII. 
Laboratory experiments revealed that predatory seastars and whelks altered the behavior of all of the many species of snails living on rocky shores in our area, and that these behavioral responses (e.g., reduced foraging, habitat shift) affected the amount of algae consumed, whereas three species of nonpredatory seastars did not. Interestingly, adult snails were not vulnerable to small species of predatory seastars, and yet they still responded to them. These results are of particular interest because they suggest that either behavioral responses in young snails might carry over to adults or that snails are vulnerable to a related species of seastar and unable to discriminate between them, necessitating further tests with an even greater taxonomic diversity of seastars. Predator identity and alarm signaling was found to elicit varying degrees of escape response, and antipredator cues were only briefly effective at high concentrations in standing water, raising doubt about the importance of TMII along wave swept rocky shores. 
Field experiments yielded mixed results regarding the importance of TMIIs. Short-term experiments in tidepools revealed an immediate flight response by snails in response to predatory seastars and a decline in species richness and diversity of mobile invertebrates over six-months. However, no change was seen in species richness or diversity of algae due to a previously unrecognized density effect that can result in an overestimation of the strength of TMIIs. In contrast, seastar and whelk predators primarily affected boulder field communities via TMII rather than DMII in the two-year experiment conducted in boulder fields, although TMIIs were context dependent (depending on disturbance and exposure to physical conditions). Our experiments are enabling us to contrast the effects these short-term behavioral responses on rocky shore communities with that of longer-term morphological responses.
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