Ecological convergence in a rocky intertidal shore metacommunity despite high spatial variability in recruitment regimes

Abstract

In open ecological systems, community structure can be determined by physically modulated processes such as the arrival of individuals from a regional pool and by local biological interactions. There is debate centering on whether niche differentiation and local interactions among species are necessary to explain macroscopic community patterns or whether the patterns can be generated by the neutral interplay of dispersal and stochastic demography among ecologically identical species. Here we evaluate how much of the observed spatial variation within a rocky intertidal metacommunity along 800 km of coastline can be explained by drift in the structure of recruits across 15 local sites. Our results show that large spatial changes in recruitment do not explain the observed spatial variation in adult local structure and that, in comparison with the large drift in structure of recruits, local adult communities converged to a common, although not unique, structure across the region. Although there is no unique adult community structure in the entire region, the observed variation represents only a small subset of the possible structures that would be expected from passive recruitment drift. Thus, in this diverse system our results do not support the idea that rocky intertidal metacommunities are structured by neutral mechanisms.community structure | ecological drift | neutral theory | interaction strength | macroecology T he extent to which the structure and diversity of natural communities is determined by interactions among species, such as predation and competition that occur at local scales, and the extent to which they are the result of regional-scale processes that can be largely independent of species interactions are central questions in ecology and are the subject of intense debate (1-4). One aspect of the debate is centered on whether niche differentiation and local interactions among species play a significant role in macroscopic community patterns (e.g., species diversity, species-abundance curves) or whether, as stated by the neutral theory of biodiversity (NTB) (2), these patterns can be generated by the neutral interplay of dispersal and stochastic demography among ecologically identical species (4-10). A related topic at the center of ecological debate since the mid-1980s is that of "supply-side" ecology (11), which proposes that the supply of individuals to local communities, a process driven largely by physical factors, can be the main determinant of population and community structure, challenging the view of control by local species interactions (12-18). If recruitment were the main determinant of adult population abundance for most species in local communities, then community structure and its spatiotemporal variation would result from environmentally driven fluctuations in the supply of individuals, largely uncorrelated with local species interactions. Similarity with the NTB argument is apparent when examining large sets of species. The fact that some static, aggregated attributes of intertidal ma...

Temporal variation in richness and composition of recruits in a diverse cnidarian assemblage of subtropical Brazil

“…It is more likely that species composition was changing in this assemblage throughout the year, with post-settlement mortality in some species thereby opening space for others (Sutherland and Karlson, 1977). Moreover, there was no convergence of year-old assemblages to a common structure in comparison to 3 mo recruitment plates, unlike the pattern observed, for instance, in rocky shores of temperate Chilean coast (Caro et al, 2010). Thus, yearly species composition on panels may be the result of several processes taking place.…”

“…High temporal variability in the species composition, richness and overall arrival rates of new recruits to benthic communities characterizes most benthic epifaunal communities (Caffey, 1985;Caro et al, 2010;Palardy and Witman, 2011;Sutherland, 1981;Watson et al, 2011). One of the explanations for these temporal changes is variation in sea surface temperature (Clarke, 2009), which interacts with annual cycles of adult reproduction and larval release, causing variability in larval availability of different species at any given time (Coma et al, 2000;Cowen and Sponaugle, 2009;Flores and Negreiros-Fransozo, 1998).…”

“…We hypothesized that 1) the long-term (yearly) and typically high hydrozoan species richness is the result of accumulation of species recruiting on different times of the year; 2) the structure (composition and abundance) of the assemblage changes over time; 3) microhabitat (sheltered or exposed plates) influence the cnidarian recruit assemblage structure; and 4) the structure of the cnidarian assemblage after one year converges to a more homogeneous configuration, different than all recruitment events, as observed for instance in rocky shore communities (Caro et al, 2010).…”

“…Species richness can and will be modulated by species interactions and differential mortality of later stages, but successful colonization, i.e. recruitment, is required to become part of the local assemblage and, in many systems, this recruitment process can leave a long-lasting signal in the diversity and relative abundance of species of the adult epifaunal community (Bertness et al, 2001;Caro et al, 2010;Hubbell, 1997;Witman, 2011, 2014;Sutherland, 1981). Since propagules of all species are not equally abundant over space and time (e.g.…”

Tumbling under the surf: wave-modulated settlement of intertidal mussels and the continuous settlement-relocation model

“…These collectors have been used extensively in recruitment studies of mussels and other invertebrate species in Chile (Narváez et al 2006, Lagos et al 2007, Caro et al 2010) and elsewhere (Menge et al 1994, Le Corre et al 2013. Collectors can be taken back to the laboratory for identification of settlers under a dissecting scope.…”