A simulation study of growth inhibition and predator resistance in Hydractinia echinata

Abstract

Abstract Field abundance patterns of Hydractinia echinata indicated the possibility that inhibitory interactions were responsible for the prevalence of this hydroid on subtidal piling substrata. A model is described which was used to augment field experiments in substantiating that predator resistance and non-aggressive spatial competition were essential attributes responsible for these observed spatial patterns. These attributes are considered to be of major adaptive significance to long-lived colonial organisms such as Hydractinia which also exhibit low rates of larval recruitment and pre-emptively utilize substratum space via vegetative growth. This model emphasizes the sessile nature of the invertebrates which comprise these communities and the importance of vegetative growth to colonial species as a means to secure substrata. The explicit inclusion of a two-dimensional spatial analogue was considered imperative because of priority effects related to larval settlement patterns, the inhibition of settlement by resident adult organisms, and growth inhibition resulting in non-transitive competitive interactions. The importance of the consideration of spatial position is discussed in terms of competitive relationships, growth form and habitat selection.