Improving an African urban mosaic for insect pollinators through increased floral diversity and better functional connectivity

Abstract

Small African urban areas are composed of an urban core, farms, and natural areas. This mosaic has high potential for providing refuge for urban biodiversity, especially for beneficial groups like insect pollinators. Insect pollinators are important for agricultural yield, yet are in decline in many parts of the world. However, to date, African urban areas as a refuge for these pollinators are poorly explored, despite increasing urbanization and agricultural intensification in recent decades. Here, we investigate how insect pollinator diversity differs between gardens, agricultural areas, and natural areas in a southern African urban mosaic. We also explore the influence of urban green spaces on the taxonomic diversity of insect pollinators. Direct observation and pan traps were used for assessing the diversity of pollinators, and we measured associated environmental, floral, and landscape variables. Results indicated similar pollinator diversity between agricultural and natural areas for some taxa, and between agricultural areas and the urban gardens for other taxa. Significantly, floral variables were the most important predictors of the pollinators, with the enhancement of floral diversity ameliorating the effects of urbanization and agricultural intensification. In contrast, landscape context was less important, although significant, for insect pollinators in these mosaics. Results, although varying significantly among taxa, suggest that agroecological farming may serve as a buffer from the effects of urbanization for natural areas and reduce the effect of urbanization on pollinators in urban gardens by providing the necessary resources. Here, we show that floral variables are important for improving urban green planning. This could be achieved by the establishment of more flowering plants, especially in human-modified areas such as semi-urban agricultural areas and urban gardens.