Test of Fox's assembly rule for functional groups in lemur communities in Madagascar

This paper examines to what extent an assembly rule designed by Fox for small terrestrial mammal communities is also applicable to communities of arboreal lemurs in Madagascar. This approach extends the testing of Fox's assembly rule to a new biogeographic region and a different phylogenetic radiation. The rule operates on a functional rather than on the taxonomic level. It specifies that: “There is a much higher probability that each species entering a community will be drawn from a different functional group, until each group is represented before the cycle repeats” (Fox, 1987: 201). This rule was tested with lemur communities from 14 sites in evergreen rain forests and nine sites in dry deciduous forests of Madagascar. Lemur species were assigned to one of three different functional groups based on dietary preferences: omnivores, frugivores, folivores. The rule applies almost perfectly to extant lemur communities in evergreen rain forest. Present communities in dry deciduous forests are not ordered as perfectly as communities of the rain forest sites, but they also deviate from random assembly as generated by the null model. Including extinct species of the dry forest ecosystem indicates that the at present unfavoured composition of the lemur community has been derived from a favoured state through extinction of the large folivorous and frugivorous lemur species. In the lemur communities of the eastern Malagasy rain forest, the assembly went through at least four, and in the Holocene dry forest ecosystem through even five, cycles without failing. This assigns considerable significance to the underlying mechanisms (most likely interspecific competition) and indicates that they are still effective in the forests of Madagascar. The dry deciduous forests might have been subject to recent natural and anthropogenic changes which interfere with the operation of these deterministic processes.