Niche Conservatism among Allopatric Species of the Grasshopper Genus Afrophlaeoba Jago, 1983 in the Eastern Arc Mountains (Tanzania)

Abstract

The persistence of species is strongly determined by their ecological niches. It is therefore, of major importance to obtain knowledge on the niche attributes of relict species in order to conserve these species and understand their current distribution patterns. Niche conservatism has been proposed to explain distribution patterns of many taxa, particularly in the tropics. Indeed, the high gamma diversity in the tropics seems to be influenced by allopatric assemblages of shared genera, whereas species overlap is often relatively low. Here, the niche overlap of allopatric Afrophlaeoba grasshopper species from the Eastern Arc Mountains (Tanzania) is studied and compared with niche overlaps among sympatric but distantly related species in the East Usambara Mountains. The results show that the genus Afrophlaeoba exhibits a strong degree of niche conservatism. All congeneric species are confined to grassy forest edges. Niche overlap within this genus was generally higher than expected by chance and higher than among sympatric species, whereas the variance of niche overlaps between species pairs was low. While the sympatric species could be distinguished ecologically using a few microhabitat variables, a comprehensive data set for the Afrophlaeoba species revealed only little resolution. The results support the hypothesis that diversification within tropical grasshoppers is not driven by niche divergence, but by allopatric isolation. Based on the niche quality of Afrophlaeoba, it is proposed that the persistence of the genus (and probably other forest taxa) might also be possible in riverine forests. There is a strong need for studies on the potential role of gallery forests as corridors for gene flow among mountain forest taxa.