Beyond neutrality: adding habitat filtering to neutral models

BackgroundUnderstanding the processes that structure species is one of the primary focuses in community ecology. Hubbell's neutral model shows stochastic processes alone can describe the two macro-ecological patterns, species richness and species-area relationship, of the community. Although Hubbell's neutral model can explain the macro-ecological patterns of the species at large scales, it paid less attention to construct the spatial structure of the community. Previous studies suggest that such spatial structures are mostly due to habitat filtering processes work at the intermediate spatial scales. Therefore, Hubbell's neutral model does not explain the full picture of the community structuring due to its fully stochastic nature.ResultsIn this study, we proposed a two-schema model that has the habitat filtering component and the stochastic component to construct the species assemblages seen in the community level. The proposed model uses one additional parameter (i.e. number of individuals in habitat) in addition to Hubbell's three-parameter neutral model (i.e. fundamental bio-diversity number (theta), dispersal limitation (m) and speciation (v)). The proposed model works at two spatial scales: habitat filtering at the intermediate scales and stochastic processes at the large and very small spatial scales. The model coupled the local community dynamics with the meta-community dynamics. The local community has a fixed area with carrying capacity that is proportional to the local community size. The number of habitats in the proposed model can vary. Individuals are placed into habitats with probabilities according to the habitat suitability. Species richness and species composition in each habitat were calculated. The model is fitted for different theta values, m values, and a different number of habitats.ConclusionsWe assume that habitat filtering plays an important role together with stochastic processes to structure species in forests. Therefore, the proposed model with only four parameters can explain a large proportion of the species structuring of the communities. We found that more species can be maintained in a heterogeneous environment than a uniform environment. Therefore, habitat conservation is highly important for maintaining species diversity in forest communities.