Inducible aggression and intraspecific competition for space in a marine bryozoan, <i>Membranipora membranacea</i>

Abstract

We experimentally investigated the causes and consequences of stolon production in the marine bryozoan Membranipora membranacea. Inducible stolons appear to mediate contests for space among conspecifics by slowing the growth of adjacent competitors. However, because stolons are produced in some but not all competitive interactions, we examined whether environmental factors such as food and hydrodynamic regime regulate their production. Furthermore, because stolons are ephemeral, persisting for only 24 h, we removed stolons to determine whether stolon production affected the outcome of competitive contests. Removing stolons from large colonies reduced their ability to surround a small neighbor, but increased their growth rate. Control colonies, producing their full complement of stolons, grew more slowly than colonies with stolons removed, suggesting that there is a tradeoff between stolon production and growth. The rate of stolon production was higher in colonies grown under lower food conditions. The likelihood that waterborne chemical or hydrodynamic cues induce stolon formation is diminished by our finding that the frequency of stolon production was unaffected by the relative positions of two interacting colonies in unidirectional flow.