Ecological convergence in a rocky intertidal shore metacommunity despite high spatial variability in recruitment regimes Andrés U. Caro, Sergio A. Navarrete1, and Juan Carlos Castilla Center for Advanced Studies in Ecology and Biodiversity and Estación Costera de Investigaciones Marinas, Pontificia Universidad Católica de Chile, Santiago, C.P. 8331150, Chile Edited by James Hemphill Brown, University of New Mexico, Albuquerque, NM, and approved September 17, 2010 (received for review May 20, 2010) In open ecological systems, community structure can be determined Instead of parameterizing a neutral model for species that by physically modulated processes such as the arrival of individuals share and compete for a common resource within a trophic level, from a regional pool and by local biological interactions. There is as required by NTB models (1, 6, 8, 19), we start with a rocky shore debate centering on whether niche differentiation and local inter- metacommunity, composed of 15 local communities of coexisting actions among species are necessary to explain macroscopic com- species from disparate taxa at all trophic levels and exhibiting an munity patterns or whether the patterns can be generated by the astonishing diversity of modes of development (Table S1). These neutral interplay of dispersal and stochastic demography among local communities are spread over 800 km of coastline and are ecologically identical species. Here we evaluate how much of the separated by tens of kilometers (Fig. 1A), surpassing the scale of observed spatial variation within a rocky intertidal metacommunity movement of all adult mobile invertebrates. In this system, we ask along 800 km of coastline can be explained by drift in the structure to what extent large-scale spatial variation in species composition of recruits across 15 local sites. Our results show that large spatial can be predicted solely by variation in dispersal and re- changes in recruitment do not explain the observed spatial variation cruitment rates. in adult local structure and that, in comparison with the large drift in Rocky intertidal communities are formed by a large proportion structure of recruits, local adult communities converged to a com- of species with complex life cycles that include an initial pelagic mon, although not unique, structure across the region. Although larval stage that lives in the water column before settling in the there is no unique adult community structure in the entire region, adult habitat. Several studies in these communities have shown the observed variation represents only a small subset of the possible that the arrival of new individuals varies greatly from site to site, structures that would be expected from passive recruitment drift. influenced largely by local and meso-scale oceanographic pro- Thus, in this diverse system our results do not support the idea cesses, and that different species appear to be affected by different that rocky intertidal metacommunities are structured by neutral larval transport mechanisms (20–25). Therefore, recruitment var- mechanisms. iation from site to site can be independent of local adult abun- dances. This open characteristic of populations over comparatively community structure | ecological drift | neutral theory | interaction large spatial scales, together with a myriad of reproductive strat- strength | macroecology egies of component species, make rocky shore invertebrate com- munities ideal systems for examining whether variation in he extent to which the structure and diversity of natural com- recruitment of multispecific assemblages from site to site is suffi- Tmunities is determined by interactions among species, such as cient to account for among-site variation in local community predation and competition that occur at local scales, and the extent structure. Conversely, postsettlement processes could erase the to which they are the result of regional-scale processes that can be signal of dispersal and buffer against spatiotemporal variation in largely independent of species interactions are central questions in the arrival of individuals. If such processes are deterministic across ecology and are the subject of intense debate (1–4). One aspect of the metacommunity, they may create structures of adult assemb- the debate is centered on whether niche differentiation and local lages that are more convergent to a common structure than would interactions among species play a significant role in macroscopic be expected by variation in the supply of individuals. Classic studies community patterns (e.g., species diversity, species-abundance consolidating the view of local control of community structure by curves) or whether, as stated by the neutral theory of biodiversity species interactions (e.g., predation, competitive exclusion) (26– (NTB) (2), these patterns can be generated by the neutral interplay 29) have focused on relatively few sites in close proximity and on sensu of dispersal and stochastic demography among ecologically iden- a small subset of strongly interacting species or modules ( fi tical species (4–10). A related topic at the center of ecological Paine, ref. 30), making it dif cult to infer the relative importance of debate since the mid-1980s is that of “supply-side” ecology (11), these processes across space for the entire community. On the which proposes that the supply of individuals to local communities, other hand, numerous studies have demonstrated the importance a process driven largely by physical factors, can be the main de- of recruitment in determining adult abundance patterns from local to regional scales (21, 31–34). However, these studies have ex- terminant of population and community structure, challenging the – view of control by local species interactions (12–18). If recruitment amined the recruit adult relationship individually for one or a few species, with widely varying results (14, 32, 35, 36). An exception is 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 fl Author contributions: A.U.C., S.A.N., and J.C.C. designed research; A.U.C., S.A.N., and J.C.C. driven uctuations in the supply of individuals, largely un- performed research; A.U.C. and S.A.N. analyzed data; and A.U.C., S.A.N., and J.C.C. wrote correlated with local species interactions. Similarity with the NTB the paper. argument is apparent when examining large sets of species. The The authors declare no conflict of interest. fact that some static, aggregated attributes of intertidal marine This article is a PNAS Direct Submission. fi communities follow predictions based on NTB (5, 8) justi es fur- 1To whom correspondence should be addressed. E-mail: [email protected]. ther evaluation of the neutrality of spatiotemporal variation in This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. marine community structure to deterministic species interactions. 1073/pnas.1007077107/-/DCSupplemental. 18528–18532 | PNAS | October 26, 2010 | vol. 107 | no. 43 www.pnas.org/cgi/doi/10.1073/pnas.1007077107 Downloaded by guest on September 26, 2021 A TEM ARR GUA PTA MOL MON CUR SEITIS QUY QUI SAL Fig. 1. Spatial variability in rates of re- cruitment and adult abundance in the meta- EN community. (A) Location of local intertidal ES communities along central Chile. (Left) The red graph shows the daily average recruitment CRU for all species per site (mean ± SE). Sites are MAT sorted from north to south, as in the map (Right). (Center) The blue graph shows adult PIC average abundance (individuals per square 0,0 0,2 0,4 0,6 0 200 400 600 800 1000 meter) at the same sites. (B) Relationship be- Recruitment rate Adults Abundance tween the dissimilarity in the recruit and adult assemblages at a given site obtained through PCA ordinations and the average recruitment rates of species at that site. Relationship with entire dataset averaged per site (three sam- B C pling dates for adults, 8 y of sampling for recruits). (C) The same relationship analyzed separately for two periods. ●, adults measured in 2006 and recruitment rates recorded in 2005. ○, adults measured in 2007 and re- cruitment rates recorded in 2005. The cyan- colored quadrangles in B and C show the dis- persion of recruit–adult distances across the region. The shape and lower boundary slope are significantly different from random ex- pectation. ARR, Arrayán; CRU, Las Cruces; CUR, Curaumilla; EN, ECIM North; ES, ECIM South; GUA, Guanaqueros; MAT, Matanzas; MOL, Los Molles; MON, Montenar; PIC, Pichilemu; PTA, Punta de Talca; QUI, El Quisco; QUY, Quintay; ECOLOGY SAL, Salinas; TEM, Temblador. the work by Forde and Ralmondi (37), who experimentally ma- munity structure of adults results simply from spatial variation in nipulated recruitment rates of two species of rocky intertidal bar- the arrival of new individuals, before niche differentiation plays nacles to evaluate their effect on community composition, a role. The rocky intertidal abundance of adults was quantified by considering a total of five species. Their results show that in early nondestructive sampling at all study sites, including six intertidal stages of succession, variability in recruitment had significant im- microhabitats, on three different survey dates. pact on community structure, but in intermediate and final stages community structure was strongly influenced by postsettlement Results and Discussion processes that produced density-dependent