The importance of renosterveld conservation based on insect diversity sampled in West Coast Renosterveld in the Western Cape of South Africa

[摘要] ENGLISH ABSTRACT: Research in the Fynbos Biome mainly focussed on the exceptional high plant diversity, especially of the Cape Floristic Region. However, there remains a poor understanding of the insect life found in this region and throughout the Fynbos Biome. The purpose of this thesis was to reduce this knowledge gap, and to add conservation value to the West Coast Renosterveld based on the insect life. This thesis is also the first to document insect diversity at community-level in a highly threatened and fragmented vegetation type in South Africa. West Coast Renosterveld, along with the other renosterveld types, is threatened by agricultural development due to the nutrient richer soils compared to the other vegetation types of the Fynbos Biome. From a conservation point of view, West Coast Renosterveld is in a critical state, with only 3-4% remaining. I used various sampling methods over four seasons to document insect species found in four West Coast Renosterveld patches in the Cape Winelands district, Western Cape. I analyse the effects of sampling methods, seasons and location on the community composition data, and calculate both alpha and beta diversity measures for the four renosterveld patches.The first part of the thesis investigated the effects of sampling method and season on the documented insect species richness and abundance of the insect communities. D-vac, sweep net, pitfall traps, and pan traps were the sampling methods used for this study. Sampling was done over all four seasons in the first year. The combined sampling methods and seasons delivered a total of 851 morphospecies, consisting of 17 orders and 155 families. The sampling methods used in the West Coast Renosterveld did not have an effect on insect species richness or abundance, but did determine how many species and what number were sampled. In addition, seasons are an important driving factor of insect communities in the remaining renosterveld areas. The sampling effort applied in this study thus suggests that renosterveld is rich in insect fauna. Furthermore, a feasible and logistical sampling strategy is proposed which can be used for future insect sampling in renosterveld and other Fynbos Biome vegetation types.The second part of the thesis compared the insect species richness and abundance of four renosterveld areas and investigated what the possible variables are affecting the variation between these areas. J.N Briers-Louw had the highest insect diversity compared to Papegaaiberg, Kooppmanskloof and Spier. Beta diversity was the smallest between any combination with J.N.Briers-Louw and yielded greater diversity when representing the whole region, compared to any other two renosterveld areas. Based on the results, it can be assumed that habitat characteristics have the biggest effect on insect diversity in renosterveld, which is altered by factors including disturbance and topography. Considering these contributing factors, this study found that insect diversity differs greatly between West Coast Renosterveld remnants with only about 20% of the species shared between patches. This emphasises the importance of conserving all remaining renosterveld patches. Also, with this study's documentation and explanation for the insect diversity found in West Coast Renosterveld, future research can now focus on specific taxa and plant-insect relationships to better understand the ecological functionality of insects in renosterveld.

[发布机构] Stellenbosch University