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

Stander, Arne (2016-12)

Thesis (MScAgric)--Stellenbosch University, 2016.

Thesis

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.

AFRIKAANS OPSOMMING: Navorsing in die Fynbos Bioom het grotendeels op die besonderse hoë plant diversiteit gefokus, veral in die Kaap Floristiese Ryk. As ʼn gevolg is daar nogsteeds ʼn gebrek aan kennis en begrip van die inseklewe in hierdie streek en die Fynbos Bioom. Die doel van die tesis was om hierdie gaping in die studieveld kleiner te maak, asook om waarde tot Weskus Renosterveld bewaring toe te voeg. Hierdie tesis is ook die eerste om insekdiversiteit op ʼn gemeenskapsvlak in ʼn hoogs bedreigde en gefragmenteerde plantegroei tipe in Suid-Afrika te dokumenteer. Weskus Renosterveld, tesame met die ander renosterveld tipes, word bedreig deur landbou ontwikkeling as gevolg van die geskikte grond wat hoër in voedingswaarde is, teenoor die ander plantegroei tipes van die Fynbos Bioom. Uit ʼn bewarings oogpunt is Weskus Renosterveld in ʼn kritieke toestand waar daar slegs ʼn oorblywende 3-4% van hierdie plantegroei-tipe oor is. Ek het verkeie versamelingsmetodes gebruik oor vier seisoene om die verskillende insekspesies te dokumenteer wat in die vier afsonderlike Weskus Renosterveld areas in die Kaapse Wynland distrik voorkom. Ek analiseer die effekte van versamilingsmetodes, seisoene en area op spesies voorkoms en getalle, en bereken beide alpha en beta diversiteitwaardes vir die vier renosterveld areas. Die eerste deel van die tesis het die effekte van versamelingsmetodes en seisoene op die gedokumenteerde insekspesies se spesiesrykheid en getalle van die insekbevolkings ondersoek. D-vac, swaainet, pitvalle, en gekleurde pan-lokvalle was die gekose versamelingsmetodes vir hierdie studie. Veldwerk was oor vier seisoene in die eerste jaar uitgevoer. Die gekombineerde versamelingsmetodes en seisoene het ʼn totaal van 851 morfospesies, wat uit 17 orders en 155 families bestaan, opgelewer. Die versamelingsmetodes het geen effek op die spesiesrykheid en getalle van die insekte gehad nie, maar het wel die hoeveelheid spesies en hul ooreenstemmende getalle bepaal. Verder is seisoen ʼn belangrike drywende faktor van insekbevolkings in die oorblywende renosterveld areas. Die geïmplimenteerde versameling van hierdie studie stel voor dat die renosterveld ryk is in insek fauna. Daar is ook ʼn gepaste en logiese versamelingsstrategie voorgestel vir verdere insekversameling in renosterveld en ander plantegroei tipes van die Fynbos Bioom. Die tweede deel van die tesis het die insekte se spesiesrykheid en getalle van die vier renosterveld areas vergelyk en het ondersoek wat die moontlike veranderlikes kan wees wat die variasie tussen hierdie areas beïnvloed. J.N. Briers-Louw het die grootste insekdiversiteit in vergelyking met Papegaaiberg, Koopmanskloof en Spier. Beta diversiteit was die kleinste tussen enige areas met J.N. Briers-Louw as kombinasie en het die grootste diversiteit wat die hele gebied verteenwoordig opgelewer, in vergelyking met enige ander twee renosterveld areas. Op grond van die resultate kan mens aanneem dat habitat karaktereienskappe die grootste effek op die insekdiversiteit van die renosterveld het, wat bepaal word deur faktore soos graad van versteuring en topografie. Deur hierdie bydraende faktore in ag te neem, het die studie bevind dat die insekdiversiteit grotendeels verskil tussen Weskus Renosterveld areas met slegs 20% van die spesies wat tussen areas gedeel word. Dit beklemtoon die belangrikheid om al die oorblywende renosterveld areas te bewaar. Met hierdie studie se dokumentasie en verduideliking van die insekdiversiteit wat in Weskus Renosterveld gevind word, kan toekomstige navorsing nou op spesifieke taksa en plant-insek verhoudings fokus om ʼn beter begrip van die ekologiese funksionaliteit van insekte in renosterveld te kry.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100209
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