species composition and pollinator efficiency of ocimum kilimandscharicum flower visitors along kakamega forest ecosystem

Abstract

Pollination is an important ecosystem service in the maintenance of biodiversity and most importantly in food production as it brings about fruit formation and seed production. Pollination is, however, on the decline due to several factors including habitat loss, exotic pest invasions, pollution, overharvesting, and land use changes. The Ocimum kilimandscharicum plant is known for its medicinal values and has gained more attention locally and internationally for its commercial use in production of pharmaceutical products. This study analyzed the flower visitors’ activity of Ocimum kilimandscharicum in Kakamega forest. Specifically, the study sought to: (i) assess the diversity and abundance of the flower visitors with increasing distance from the forest edge(ii) assess the effects of temperature and precipitation on flower visitors’ diversity and (iii) Identify the most efficient flower visitor using seed set analysis. Data were collected through direct observations and sweep-netting for specific objective one and two. Data collection for specific objective three involved the bagging method where flowers were covered using a pollinator bag pre-anthesis and allowed a single visit from a flower visitor. The pollinator was then captured and a color tag attached to the flower. Seed sets from the flowers were collected and counted. Six study sites were identified along two transect each 2.5 km long and labeled A to F. Distance in meters from the forest edge for each site was; A=221, B=72, C=83, D=198, E=113 and F=50. Diversity indices of different flower visitors was calculated using the Shannon-Wiener diversity index. One-way analysis of variance was used to compare significant differences between sites and a two sample t – test was used to identify mean significant differences in species diversity between the closest and the furthest sites. A total of 645 individuals belonging to 35 species were captured from 4 families; Apidae, Megachilidae, Halictidae and Collectidae. The highest diversity was at Site F (H’ = 2.38) which was closest to the forest edge and the lowest diversity was from Site A (H’ = 1.44) which was furthest from the forest edge. Distance from the forest edge significantly influenced species diversity (F (3, 20) = 14.67, p = 0.024). Distance from the forest edge also significantly influenced species abundance between the furthest sites A, D and E and the nearest sites F, B and C to the forest edge (p=0.0315) and species richness (p=0.0187). There were no significant correlations between; temperature/species richness, temperature/diversity, precipitation/species richness and precipitation/diversity. The highest number of seed set, 12,944 was collected under the Apis mellifera making this species, the most efficient pollinators. Apis mellifera also had the highest visitation frequency at 30. This study shows that Ocimum kilimandscharicum flower visitors play essential roles in pollination and the higher the number of visits, the higher the number of seeds set. Many of these pollinators are associated with the forest hence the need to conserve the Kakamega forest as a source pool for pollinators. This pool of pollinators has direct implications on food security to communities surrounding the forest. Further studies are required to determine the extended roles of these pollinators on the surrounding farmlands.