Community diversity and the population abundance of a particular group of species are controlled by immediate environment, inter and intra species interactions, landscape conditions, historical events and evolutionary processes. Nestedness is a measure of order in an ecological system, referring to the order in which the number of species is related to area or other factors. In this study we study the nestedness pattern in stream diatom assemblages in 24 stream sites of Central Western Ghats. The present investigation reports 98 taxa from the streams of Central Western Ghats region. The communities show highly significant nested pattern (T = 16.41°C p = 4.43e-31, matrix fill 14%) and mean T = 50.61(±2.88) °C. The Mantel test of matrix revealed a strong relationship between species assemblages and environmental condition at sites. There is no significant relationship in the species assemblage or the environmental condition with geographical distance. However the relationship of species assemblages with environmental condition was highly significant. Principal component analysis indicated that environmental conditions differed markedly across the sampling sites with the first three components explaining 78% of variance. Species composition of diatoms in tropical streams of Central Western Ghats is significantly correlated with environmental distance across geographical extent. The current pattern suggests that at regional level of Western Ghats, that local micro environment control rather than the effect of dispersal limitations on the species composition of epilithic diatoms in streams. The nestedness showed by the diatom community was highly significant, even though it had quite a high proportion of idiosyncratic species, characterized with high numbers of cosmopolitan species, whereas the nested species were dominated by endemic species. PCA identify ionic parameters and nutrients as the major features which determine the characteristics of the sampling sites, hence the local water quality parameters are the major driver in deciding the diatoms species assemblages.
Keywords: Diatoms, Western Ghats, Nestedness, Idiosyncratic species, PCA