Document: CHR-3-78-2

The use of a matrix model to study indirect effects in a hermit crab-hydroid symbiosis.

DAMIANI, C.*

Duke University, Durham, NC 27708 ¹

Abstract:
Indirect effects may play an important role in determining how changes in the biotic environment influence the nature of host-symbiont interactions. However, since direct and indirect effects often act on different demographic rates, it can be challenging to compare the relative importance of these two types of interactions. For example, the hydroid Hydractinia symbiolongicarpus has been shown to have negative direct effects on the fecundity of its host hermit crab Pagurus longicarpus, and positive indirect effects on survival. In this study, I combined field experiments with a matrix model to integrate the hydroid's effects on different demographic rates into a common measure (population growth rate), which I used to quantify the relative contributions of direct and indirect effects to the net interaction. I found that indirect effects contributed strongly to the net interaction in the presence of fish predators, but weakly in the presence of crab predators, resulting in a symbiosis that shifts between parasitism and mutualism.

Keywords: symbiosis, indirect effects, matrix models

This abstract is being presented at: 9:45 AM in session:
Oral Session #7: Aquatic Ecology: Shellfish to Snails.