Beyond the continuum: a multi-dimensional phase space for neutral–niche community assemblyby Guillaume Latombe, Cang Hui, Melodie A. McGeoch

Proceedings of the Royal Society B: Biological Sciences




Cite this article: Latombe G, Hui C, McGeoch

MA. 2015 Beyond the continuum: a multidimensional phase space for neutral–niche community assembly. Proc. R. Soc. B 282: 20152417.

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Guillaume Latombe

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Beyond the continuum: a multidimensional space that uses community processes (such as dispersal and niche on December 23, 2015 from at or via guillaume.latombe@monash.eduecology, environmental science

Keywords: community, neutral–niche continuum, filter paradigm, neutral theory, metacommunity ecology, macroecological patternsReceived: 11 October 2015

Accepted: 13 November 2015rspb.royalsocietypublishing.orgselection) to define the limiting neutral and niche conditions and to test the continuum hypothesis. We compare the outputs of modelled communities in a heterogeneous landscape, assembled by pure neutral, pure niche and composite processes. Differences in patterns under different combinations of processes in

CAPS reveal hidden complexity in neutral–niche community dynamics. The neutral–niche continuum only holds for strong dispersal limitation and niche separation. For weaker dispersal limitation and niche separation, neutral and niche processes amplify each other via feedbackwith the environment. This generates patterns that lie well beyond those predicted by a continuum. Inferences drawn frompatterns about community assembly processes can therefore bemisguided when based on the continuum perspective. CAPS also demonstrates the complementary information value of different patterns for inferring community processes andcaptures the complexityof communityassembly. It provides ageneral tool for studying the processes structuring communities and can be applied to address a range of questions in community and metacommunity ecology. 1. Background

The two dominant theories on the development and structure of communities are niche and neutral theory. Niche theory explains the structure of communities using the relationship between species traits and habitat characteristics.

Meanwhile, neutral theory assumes a fixed species pool in the absence of speciation and invasion, and considers all species to be ecologically equivalent, with stochastic dispersal and ecological drift being the only processes determining community structure. Despite contrasting opinions on the value of neutral theory [1,2], it is now generally accepted that neutral and niche processes interact in natural communities and both contribute towards the structure of species assemblages [3]. The relative roles of neutral and niche processes have been shown to differ across spatio-temporal scales [4,5] and modelling these processes in combination (composite models) better represents biological patterns than neutral or niche models alone [6,7].

Two composite-model approaches have been used to jointly examine niche and neutral processes in communities. A phenomenological approach involves directly modelling the abundance of species using differential equations and probability distributions, taking interactions between species into account (e.g. [6,8–10]). By contrast, a mechanistic approach is based on a ‘filter & 2015 The Author(s) Published by the Royal Society. All rights reserved.dimensional phase space for neutral– niche community assembly

Guillaume Latombe1, Cang Hui2,3 and Melodie A. McGeoch1 1School of Biological Sciences, Monash University, Melbourne 3800, Australia 2Centre for Invasion Biology, Department of Mathematical Sciences, Stellenbosch University, Matieland 7602,

South Africa 3African Institute for Mathematical Sciences, Cape Town 7945, South Africa

CH, 0000-0002-3660-8160

Neutral and niche processes are generally considered to interact in natural communities along a continuum, exhibiting community patterns bounded by pure neutral and pure niche processes. The continuum concept uses niche separation, an attribute of the community, to test the hypothesis that communities are bounded by pure niche or pure neutral conditions. It does not accommodate interactions via feedback between processes and the environment. By contrast, we introduce the Community Assembly Phase Space (CAPS), a multifor neutral and niche processes

Proc.R.Soc.B 282:20152417 2 on December 23, 2015 from paradigm’ [11,12], where propagules pass through a succession of filters that structure the community (figure 1a).

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]. 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. the strength of interspecific competition (see also [7,9]).