Implications of fragile landscapes for endemic pollinators in an eastern afro-montane biodiversity hotspot of Kenya

Abstract

This study was carried out to determine how disturbances could shape the natural occurrence of African meliponine bee species in different ecological habitats of Taita hills of Kenya and how this could lead to changes in their diversity. Habitats sampled were indigenous forests, exotic forests, mixed highland forests, Acacia dominated bush lands, mixed deciduous woodlands and grasslands which were further categorized as either fragmented or un-fragmented habitats based on levels of disturbance. The study sites were chosen based on various features such as, forest fragment size, level of forest fragment isolation, forest fragment age, and level of degradation. In all study locations, meliponine bee species were sampled using the conventional complementary method, belt transect (direct observation of nesting colonies synonymous to a visual census) from the months of March to September 2014 (combining both the long rainy season and dry season). Nesting colonies of the 4 meliponine bee species, namely, Hypotrigona gribodoi, Meliponula ferruginea (black), Hypotrigona ruspolii and Plebeina hildebrandti, were surveyed following a successive gradient. In each study site (25 ha), 20 linear transects of 250 m × 20 m each were established using a global positioning system (GPS) receiver to mark coordinates with relation to habitat type. Data such as nesting site/substrate, GPS coordinates of nest, and names of nesting trees were recorded. A total of four species depicted by the Renyi diversity profile was recorded in five out of the six main habitat types surveyed and a further extrapolation with Shannon index (EH) also predicted the highest species richness of 4.24 in a deciduous habitat type with more trees and vegetation and the lowest species of 1.01 in isolated forest patches habitat type. These meliponine bee species (Hypotrigona gribodoi, Hypotrigona ruspolii, Meliponula ferruginea (black) and Plebeina hildebrandti) were observed to be unevenly distributed across all six sampled habitats, further indicating that mixed deciduous habitat proved to be more diverse than Acacia dominated bush lands, grasslands and exotic forest strips which have all undergone varying levels of fragmentation. This has revealed that unprecedented conversions of natural habitats leading to fragmentations of such habitats is a key driving factor causing  increased habitat isolation and vulnerability in this afro-montane region which may potentially distort local assemblages of native pollinators such as meliponine bee species.

Keywords: Meliponine bees, habitat fragmentation, diversity, Eastern Afro Montane