Spatiotemporal dynamics of insect diversity in tropical seasonal forests is linked to season and elevation, a case from northern Thailand
Résumé
Seasonal forests with alternating wet and dry seasons are geographically predominant in the tropics but little is known of the spatiotemporal dynamics of the megadiverse insect communities inhabiting them. We studied variation in diversity and abundance parameters of two taxonomically and functionally distinct insect orders, Diptera and Auchenorrhyncha throughout 12 months across a 2,100 m elevation gradient in seasonal forests in northern Thailand. The interactions of space (elevation) and time (successive months of the year) on species richness, abundance, evenness and local community turnover were interpreted on spatiotemporal grids. We found that: (1) The spatiotemporal dynamics of diversity parameters are taxon-dependent. (2) Diversity of Diptera and Auchenorrhyncha broadly correlates with monsoon rains despite taxonomic and functional dissimilarity. (3) Peak diversity and abundance of Diptera and Auchenorrhyncha occurred at different elevations and for different durations during the wet season but with bimodal peaks coinciding with early-and late-monsoon periods. (4) Species-rich early-monsoon assemblages had greater evenness than relatively depauperate late-monsoon assemblages. (5) Higher elevation assemblages have greater temporal stability suggesting that they are less seasonally constrained than low-elevation assemblages; they had proportionally more species with longer activity periods. Our results emphasise that seasonality is an under-recognised variable in insect diversity studies and since diversity and its structure are closely linked to climatic seasonality in globally extensive tropical seasonal forests, any assessment of global biodiversity by extrapolation from local and regional measurements requires that seasonal patterns be recognised.