Functional diversity of habitat formers declines scale-dependently across an environmental stress gradient
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COMMUNITY ECOLOGY – ORIGINAL RESEARCH
Functional diversity of habitat formers declines scale‑dependently across an environmental stress gradient Laura Cappelatti1 · Alizée R. L. Mauffrey1 · John N. Griffin1 Received: 15 December 2019 / Accepted: 27 August 2020 © The Author(s) 2020
Abstract Marine habitat formers such as seaweeds and corals are lynchpins of coastal ecosystems, but their functional diversity and how it varies with scale and context remains poorly studied. Here, we investigate the functional diversity of seaweed assemblages across the rocky intertidal stress gradient at large (zones) and small (quadrat) scales. We quantified complementary metrics of emergent group richness, functional richness (functional space occupied) and functional dispersion (trait complementarity of dominant species). With increasing shore height, under species loss and turnover, responses of functional diversity were scale- and metric-dependent. At the large scale, functional richness contracted while—notwithstanding a decline in redundancy—emergent group richness and functional dispersion were both invariant. At the small scale, all measures declined, with the strongest responses evident for functional and emergent group richness. Comparisons of observed versus expected values based on null models revealed that functional richness and dispersion were greater than expected in the low shore but converged with expected values higher on the shore. These results show that functional diversity of assemblages of marine habitat formers can be especially responsive to environmental stress gradients at small scales and for richness measures. Furthermore, niche-based processes at the small—neighbourhood—scale can favour co-occurrence of functionally distinctive species under low, but not high, stress, magnifying differences in functional diversity across environmental gradients. As assemblages of marine habitat formers face accelerating environmental change, further studies examining multiple aspects of functional diversity are needed to elucidate patterns, processes, and ecosystem consequences of community (dis-)assembly across diverse groups. Keywords Emersion gradient · Seaweed · Functional traits · Emergent groups · Assembly patterns
Introduction Biodiversity is increasingly recognised as multidimensional, including taxonomic, phylogenetic, and functional components (Cadotte et al. 2009; Devictor et al. 2010; Stevens and Gavilanez 2015). Functional traits such as body size, mouthpart- or leaf- morphology determine an organism’s capacity to process resources and how it experiences Communicated by Daniel C Reed . Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00442-020-04746-1) contains supplementary material, which is available to authorized users. * Laura Cappelatti [email protected] 1
Biosciences Department, Swansea University, Wallace Building, Swansea SA2 8PP, Wales, UK
and interacts with its environment. The diversity of such traits—functional diversity—cap
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