Assessing evidence for random assembly of marine benthic communities from regional species pools

Abstract

Local species diversity may be determined by processes operating locally, such as disturbance, predation and competition, or by regional processes, such as environmental structuring or history. Classical theory focusing on competition predicts that the species combining to form communities will be less similar to each other than they would be if they were assembled at random from a regional species pool. Theory focusing on environmental structuring predicts that species will be more similar to each other than expected by chance. A randomisation test that determines the extent to which local species lists represent random selections from a regional list, based on the average relatedness between species, was applied to data held in the MacroBen database. Little or no evidence was found for species lists of whole faunas at any scale being random subsets of species lists at larger scales. Species tend to be more closely related to each other than would be expected if they were assembled at random. Thus marine soft-sediment macrofauna are not locally assembled at random from regional species pools and it is likely that regional processes determine the assembly of communities. Focusing on the most abundant class within the macrofauna, a different pattern emerges, in that there is a much stronger tendency for local polychaete composition to be a random subset from regional pools at all scales. Thus it is not possible to determine whether local polychaete diversity is independent of both local and regional processes, or determined by a combination of both acting antagonistically.

Species diversity, functional complexity and rarity in Arctic fjordic versus open shelf benthic systems

“…Witman et al (2004) showed that, on a global scale, local species richness is strongly related to regional species pools in epifaunal benthic communities encrusting subtidal rocks. For soft-bottom North Atlantic benthic communities, Renaud et al (2009) found a positive relationship between the local and regional species richness, while Somerfield et al (2009) showed that at different spatial levels, local communities were not random subsets of re gional species pools, and tended to be composed of species more closely related (i.e. having similar tolerances to environmental stressors and shared functional traits) than if selected randomly.…”

Large-scale studies of the European benthos: the MacroBen database

“…Somerfield et al (2009, this Theme Section) examine whether local macroinfaunal communities may be assembled at random from regional species pools at a range of spatial scales, concluding that this is not the case and that regional processes probably influence community assembly. Different processes determine the assembly of whole communities and of the polychaete component of those communities.…”

Can coastal biodiversity measured in four Mediterranean sites be representative of the region? A test for the robustness of the NaGISA protocol by using the hard substrate syllid (Annelida, Polychaeta) taxo-communities as a surrogate

“…the processes through which species form communities) is influenced by a variety of factors which often result in a non-random composition of the species pool. Ecologists recognise two major patterns of how benthic assembly is directed (Somerfield et al, 2009): (a) through high competition between similar species, thus leading to an equilibrium with a high variety of traits and very dissimilar species (e.g. Wilson & Gitay, 1995), and (b) environmental filtering (environmental structuring or history), through which a given set of environmental variables allows only species with certain traits to survive and establish a population, thus leading to a community comprised of species similar to each other (e.g.…”