Spatio-temporal patterns of hover fly (Diptera: Syrphidae) diversity across three habitat types in KwaZulu-Natal, South Africa.

Abstract

Hover flies (Diptera: Syrphidae) are poorly studied in southern Africa and as a result, little is known about their abundance throughout the year. Hover fly abundance is generally expected to vary according to vegetation types, due to differences in the type and diversity of floral resources, but this has not yet been investigated in South Africa. This study aims to investigate temporal and spatial patterns of hover flies across three different, but adjacent habitats (forest, grassland, and plantation) in KwaZulu-Natal (South Africa). This was done in two ways, first, by analysing occurrence data from the Global Biodiversity Information Facility’s (GBIF) database across months of the year. Second, by quantifying fly presence and abundance using Malaise traps set up in three different habitats and supplemented with hand-netting data. The Malaise traps were set up from October 2020 - September 2021 and were generally serviced weekly. Hover flies were sorted and identified using available keys at the KwaZulu-Natal Museum. The KZN GBIF database contained 11 tribes that represented three distinct phenological patterns. The Karkloof GBIF dataset contained seven tribes that represented two distinct phenological patterns. The field collection dataset contained eight tribes that represented two distinct monthly patterns, although these slightly differed from the patterns found in the GBIF data. Most records were from January, September and December whereas few records were from May, June and July. Minimum-minimum, average-minimum, average maximum and average temperature showed a positive correlation with hover fly abundance. In terms of spatial patterns, grassland had the highest number of adult hover fly individuals (154), followed by forest (106) and plantation (20). There was an overall effect of habitat type on both the mean number of species and the number of individuals per trap per week. In addition, Shannon’s diversity showed variation among the three habitat types whereas Simpsons Evenness index showed no variation. The results show that hover fly populations remain active throughout the year, but with distinct fluctuations in their abundance. They also show that heterogeneous indigenous habitats such as grassland and forest represent high abundance, diversity, evenness and richness of hover flies and this may be due to the diversity in available microhabitats, compared to the plantation, which is a modified habitat that lacks microhabitat diversity. Nonetheless, further studies should be undertaken in different regions of South Africa to better understand the monthly patterns as well as the effect of habitat type on hover fly diversity.