Reconciling niche and neutrality: the continuum hypothesis

Abstract

In this study, we ask if instead of being fundamentally opposed, niche and neutral theories could simply be located at the extremes of a continuum. First, we present a model of recruitment probabilities that combines both niche and neutral processes. From this model, we predict and test whether the relative importance of niche vs. neutral processes in controlling community dynamics will vary depending on community species richness, niche overlap and dispersal capabilities of species (both local and long distance). Results demonstrate that niche and neutrality form ends of a continuum from competitive to stochastic exclusion. In the absence of immigration, competitive exclusion tends to create a regular spacing of niches. However, immigration prevents the establishment of a limiting similarity. The equilibrium community consists of a set of complementary and redundant species, with their abundance determined, respectively, by the distribution of environmental conditions and the amount of immigration.

Beyond the continuum: a multi-dimensional phase space for neutral–niche community assembly

“…It is based on the variability in the outputs of independent simulation model replicates in a spatially explicit, composite model of plant communities. With this definition, Gravel et al [13] compute a neutrality index using the variability in species abundance, whereas Bar-Massada et al [3] use the variability in the species identity occupying a cell. In these models, strict niche separation leads to a deterministic output with no variability because one habitat can only be occupied by one particular species.…”

“…A different way of defining neutrality along the continuum has also been proposed to account for both distance-limited dispersal and niche separation [3,13]. It is based on the variability in the outputs of independent simulation model replicates in a spatially explicit, composite model of plant communities.…”

“…These filters are defined by interactions between the propagules and their surrounding environment, favouring some individuals and species over others during the colonization of empty sites. The number of filters can vary depending on the conceptual model [5,7,13], but there are two general successive filters: a neutral dispersal filter representing the probability of propagules reaching a given location, and a niche filter, representing their probability of survival in the location based on biotic and abiotic conditions, i.e. based on niche selection [13].…”

“…The number of filters can vary depending on the conceptual model [5,7,13], but there are two general successive filters: a neutral dispersal filter representing the probability of propagules reaching a given location, and a niche filter, representing their probability of survival in the location based on biotic and abiotic conditions, i.e. based on niche selection [13]. Although these composite models are increasingly used to describe community dynamics, the way in which neutral and niche processes interact and their relative importance in structuring communities is still unclear [3].…”

“…The neutral-niche continuum proposes that natural communities lie along a continuum based on the relative importance of these processes, with pure neutral-(no or equal niche selection amongst species) and pure niche-(strict niche separation; each species survives under a single, unique set of environmental conditions) driven communities at either extreme [3,10,13]. For example, Mutshinda & O'Hara [10] locate a community along the continuum using a neutrality index (bounded between 0 and 1), computed as the degree of average niche overlap, i.e.…”