Structural patterns of a coastal hermit crab-gastropod shell interaction network: new insights from a unique relationship

Abstract

Hermit crabs are ideal organisms for assessing how species that share resources can coexist, as these crustacean species have an intimate relationship with gastropod shells and therefore compete for this particular resource. There is compelling evidence that hermit crabs do not interact with gastropod shells randomly, but few studies have investigated the community-level interactions between hermit crabs and shells. Here we used network analyses to present the first community-level assessment of the structure of a hermit crab-shell interaction network in a coastal region in southeastern Brazil in order to identify mechanisms that underlie hermit crab coexistence. Our results show that the hermit crab-gastropod shell interaction network was non-nested, specialized, and modular. The modular network structure revealed differences in resource use among hermit crab species. The network structure departs from those of free-living species in which the lack of interaction intimacy between species leads to a nested pattern. Thus, the morphological specialization of hermit crabs in relation to their host shells appears to play an important role in structuring the community-level interaction network. Future studies should evaluate the relative importance of abundance and functional traits in the structure of this unique interaction network.