Floral turnover and climate drive seasonal bee diversityalong a tropical elevation gradient

Abstract

The contribution of seasonality in species communities to elevational diversityof tropical insects remains poorly understood. We here assessed seasonal pat-terns and drivers of bee diversity in the Eastern Afromontane BiodiversityHotspot, Kenya, to understand the contribution of seasonality to elevationalbiodiversity patterns. Bee species and plant species visited by bees wererecorded on 50 study plots in regrowth vegetation across four major seasonsalong two elevation gradients from 525 to 2530 m above sea level. Bees weresampled by transect walks using sweep nets and aspirators. We examined howlocal species richness (α-diversity) and seasonal changes in local species com-munities (β-diversity) contribute to species richness across seasons (γ-diversity)along elevation gradients. Using a multimodel inference framework, we identi-fied the contribution of climate and floral seasonality to elevational patterns inbee diversity. We found that bothα- andγ-diversity decreased with elevation.Seasonalβ-diversity decreased with elevation and the high turnover of speciesacross seasons contributed to a considerably higherγ- thanα-diversity onstudy plots. A combination of seasonality in climate and the seasonal turnoverof floral resources best explained the seasonality in bee species communities(seasonalβ-diversity). We, therefore, conclude that, despite the more stable,and favorable climatic conditions in the tropics (in comparison to temperateregions), climatic seasonality and its influence on bees’floral resources largelydetermined seasonal patterns of bee species diversity along elevation gradientson tropical mountains.