Floral turnover and climate drive seasonal bee diversity along a tropical elevation gradient

Abstract

The contribution of seasonality in species communities to elevational diversity of tropical insects remains poorly understood. We here assessed seasonal patterns and drivers of bee diversity in the Eastern Afromontane Biodiversity Hotspot, Kenya, to understand the contribution of seasonality to elevational biodiversity patterns. Bee species and plant species visited by bees were recorded on 50 study plots in regrowth vegetation across four major seasons along two elevation gradients from 525 to 2530 m above sea level. Bees were sampled by transect walks using sweep nets and aspirators. We examined how local species richness (α-diversity) and seasonal changes in local species communities (β-diversity) contribute to species richness across seasons (γ-diversity) along elevation gradients. Using a multimodel inference framework, we identified the contribution of climate and floral seasonality to elevational patterns in bee diversity. We found that both αand γ-diversity decreased with elevation. Seasonal β-diversity decreased with elevation and the high turnover of species across seasons contributed to a considerably higher γthan α-diversity on study plots. A combination of seasonality in climate and the seasonal turnover of floral resources best explained the seasonality in bee species communities (seasonal β-diversity). We, therefore, conclude that, despite the more stable, and favorable climatic conditions in the tropics (in comparison to temperate regions), climatic seasonality and its influence on bees' floral resources largely determined seasonal patterns of bee species diversity along elevation gradients on tropical mountains.

Seasonal and elevational changes of plant‐pollinator interaction networks in East African mountains

“…Seasonality is known to shape the period of species occurrence and their interaction patterns. More so, a detailed seasonal turnover of bees and bee‐visited plant species has been reported for this region (see Dzekashu et al, 2022). Here, we observed an increase in nestedness with elevation, though it did not differ across seasons, following similar patterns of complete network interactions described above.…”

“…We can argue this to be a result of reduced interdependence at higher elevations due to the increase in generality, hence the increasing connectance during the warm‐wet season (Classen et al, 2020). Moreover, the high seasonal turnover of species along these elevation gradients (Dzekashu et al, 2022) might prevent the aggregation of a more compact structure, hence the inconsistencies in observed connectance across seasons.…”

“…We examined the impact of climatic (MMT, MMP), flower ( F γ ), and bee ( b γ, log(abun)) parameters on overall network structures. We calculated bee species diversity ( b γ ) as the cumulative bee species richness per study plot across the cold‐dry and warm‐wet seasons, respectively (e.g., Dzekashu et al, 2022). To obtain a measure of the diversity of bee‐visited plants, we calculated the species diversity of plants ( F γ ) using the same approach as that employed for the bees.…”

“…Farming and grazing activities are equally carried out and several honeybee hives are deployed by local indigenes into the forested highlands. Along the elevation gradient, the landscape is made up of savannah, shrublands, indigenous bushlands, pasture, and human settlement with some subsistence farming activities (Dzekashu et al, 2022). Seasonality in climate is pronounced in the study region.…”

Disentangling the effects of different human disturbances on multifaceted biodiversity indices in freshwater fish

“…Environmental factors played an important role in the response of indices, with a strong negative effect of temperature and rainfall seasonality on several indices. It has already been showed that seasonality strongly impacts diversity of communities in tropical terrestrial ecosystems (Correa et al, 2021; Dzekashu et al, 2022; Oita et al, 2021) but few studies highlighted such a result in lotic ecosystems, especially temperate (Epele et al, 2022; Li et al, 2019). Most studies in lotic ecosystems (Faulks et al, 2011) but also in other ecosystems highlighted the predominance of environmental factors such as altitude or temperature seasonality (Howard et al, 2019).…”