How do habitat filtering and niche conservatism affect community composition at different taxonomic resolutions?
Résumé
Understanding how local species assembly depends on the regional biogeographicand environmental context is a challenging task in community ecology. In spatiallyimplicit neutral models, a single immigration parameter, I(k), represents the flux of immigrantsfrom a regional pool that compete with local offspring for establishment in communities. Thisflux counterbalances the effect of local stochastic extinctions to maintain local speciesdiversity. If some species within the regional pool are not adapted to the local environment(habitat filtering), the migrant flux is reduced beyond that of the neutral model, such thathabitat filtering influences the value of I(k) in non-neutral situations. Here, we propose a novelmodel in which immigrants from the regional pool are filtered according to their habitatpreferences and the local environment, while taxa potentially retain habitat preferences fromtheir ancestors (niche conservatism). Using both analytical reasoning and simulations, wedemonstrate that I(k) is expected to be constant when estimated based on the communitycomposition at several taxonomic levels, not only under neutral assumptions, but also whenhabitat filtering occurs, unless there is substantial niche conservatism. In the latter case, I(k) isexpected to decrease when estimated based on the composition at species to genus and familylevels, thus allowing a signature of niche conservatism to be detected by simply comparing I(k)estimates across taxonomic levels. We applied this approach to three rain forest data sets fromSouth India and Central America and found no significant signature of niche conservatismwhen I(k) was compared across taxonomic levels, except at the family level in South India. Wefurther observed more limited immigration in South Indian forests, supporting the hypothesisof a greater impact of habitat filtering and heterogeneity there than in Central America. Ourresults highlight the relevance of studying variations of I(k) in space and across taxonomiclevels to test hypotheses about the ecological and evolutionary drivers of biodiversity patterns.