Biodiversity of stream insects in the Malaysian Peninsula: spatial patterns and environmental constraints

The spatial variation in Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxonomic composition in headwater forested streams of peninsular Malaysia was studied. Several environmental parameters were assessed for their importance in regulating the composition of assemblages across the spatial extent of the Malaysian bioregion. The spatial variables were expressed as vectors based on principal coordinates of neighbour matrices (PCNM). The forward selection based on two stopping criteria was used to identify the key environmental and spatial variables controlling the EPT taxonomic composition. Eigenvector-based spatial filtering was employed to investigate spatial patterns in EPT composition, and the variation partitioning technique was used to determine the relative importance of environmental and spatial factors in application on EPT composition. The forward selection retained five parameters [altitude, biochemical oxygen demand (BOD), water velocity, ammonia, and dissolved oxygen (DO)] which explained 13.2% of the total variance in EPT composition. The three selected spatial variables (PCNM vectors) accounted for 8.4% of the composition variation. However, the spatially-structured environmental variables explained 7.5% of the total variance in EPT composition. The variation in altitude correlated with broad-scale spatial extent and was the most important factor regulating the EPT composition in peninsular Malaysia. Our study revealed spatially-structured patterns in the EPT composition, showing a richness decrease from the south to the north of peninsular Malaysia.