Tolerance-differentiation among species: a realistic and parsimonious resolution to the niche versus neutrality debate?
Pither, Jason*,1, Kerkhoff, Andrew1, Enquist, Brian1, 1 University of Arizona, Tucson
ABSTRACT- The assumption that plant species are differentiated primarily with respect to their environmental optima rather than by their tolerances pervades theoretical ecology research, and is implicit to common interpretations of statistical correlations between community structure and environment. However, experimental work and meta-analyses suggest that a tolerance-differentiation model (TDM) may be more realistic. Here we use a metacommunity simulation model coupled with realistically-structured environmental landscapes to explore the conditions under which a TDM can generate ecological patterns similar to those produced by a distinct-preferences model (DPM) of niche differentiation. Under a variety of realistic scenarios, both models generate statistical patterns that would traditionally be ascribed to the DPM. For instance, highly significant partial Mantel correlations between community compositional dissimilarity, environmental dissimilarity, and geographical distance emerge under both a TDM and a DPM. Surprisingly, even neutral dynamics occurring on landscapes with typical environmental heterogeneity can elicit statistically significant community-environment correlations, though these are substantially smaller in magnitude. Of particular importance is the observation that the traditional hallmarks of niche-differentiation (segregation of species along gradients) can arise through the dynamics of a comparatively small contingent of specialized species. Our findings provide (i) a suite of alternative, realistic, and parsimonious resolutions to the niche versus neutrality debate, and (ii) convincing reasons to question the assumption – widely adopted in applied ecology research (e.g. climate-envelope modelling, paleolimnology) – that realized environmental niches serve as reliable proxies for fundamental environmental niches.
Key words: niche, metacommunity, neutral, model
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