Conservation in human-influenced areas : epigaeic arthropods in the Cape Floristic Region Lowlands

Boonzaaier, Carmen (2006-12)

Thesis (MSc)--University of Stellenbosch, 2006.

Thesis

ENGLISH ABSTRACT: The conservation of biodiversity is becoming increasingly challenging as habitats are disturbed, fragmented or destroyed. Although nature reserves now cover more than 10 % of the earths’ surface it has become clear that more will have to be done to ensure the long-term survival of species. Therefore, focus is increasingly shifting towards conserving biodiversity in natural and semi-natural remnants in human-influenced areas. This study aimed to determine the contribution of remnants in human-influenced areas to the conservation of biodiversity in the Cape Floristic Region (CFR) lowlands, using ground-dwelling arthropods, specifically ants, as the focal taxon. Initially, base-line information of arthropods and in particular ants was obtained. Sampling arthropods generally involves a large sample effort. Therefore maximizing sampling effort for ants in the CFR was investigated by trapping ground-dwelling ants at a single locality. Doubling the number of grids of pitfall traps was found to be more effective in trapping a greater number of species than doubling the duration of sampling. Therefore increasing spatial sampling intensity rather than sampling duration maximizes sample effort for CFR ants. Also, the seasonal changes of ground-dwelling arthropods, including ants, were determined by sampling four times during the year at a single locality. Overall arthropod abundance was found to peak in summer while dropping to a minimum in winter. This pattern was mirrored by that of the ants, indicating that ant results have a broader relevance than to ants only. The ground-dwelling fauna was dominated by ants emphasizing their importance in the CFR lowlands, and demonstrating that ants are an appropriate flagship taxon for epigaeic arthropod diversity in the CFR. Finally the contribution of remnants in human-influenced areas to the conservation of the CFR was investigated. A nested hierarchical approach was used, where five localities were selected across the CFR, each containing one reserve site and one site with natural remnants. Ants were sampled, along with environmental variables, namely weather, vegetation and soil. Overall, remnants were found to support similar ant assemblages to those of reserves. However for individual localities some remnants were significantly different to their reserve counterparts. Differences in ant assemblages were found to be greater between localities than between reserves and remnants. The relatively high heterogeneity of ants found in this study emphasizes the conservation significance of invertebrates along with that of plants in the CFR. Remnants clearly show the potential to conserve ant assemblages, however correct management is needed for these areas to maximize their potential. Disturbances such as the presence of the invasive Argentine ant and increasing soil nutrients by fertilization, pose a distinct threat to the ability of remnants to conserve ant assemblages. This study has shown that remnants currently support ant assemblages representative of those present in the CFR today. Therefore, some remnant patches of habitat in agricultural areas currently do contribute highly to the conservation of a functional important taxon in this global biodiversity hotspot, and if managed correctly, may continue to do so in the future.

AFRIKAANSE OPSOMMING: Die vernietiging en fragmentering van habitatte maak die bewaring van biodiversiteit al hoe meer van ‘n uitdaging. Alhoewel natuur reservate reeds meer as 10 % van die aarde se oppervlak beslaan is dit duidelik dat meer gedoen sal moet word vir die lang-termyn voortbestaan van spesies. Dus word die fokus van biodiversiteit-bewaring toenemend gerig op bewaring van natuurlike en semi-natuurlike fragmente in menslik-beinvloede gebiede. Die doel van hierdie studie was om te bepaal wat die bydrae van fragmente van natuurlike veld in menslik-beinvloede gebiede is tot die bewaring van die streek. Dit is gedoen deur van grond-lewende geleedpotiges en spesifiek, miere in die Kaapse floraryk (CFR) gebruik te maak. Aanvanklik is kennis ingewin oor die geleedpotiges en spesifiek miere in die omgewing. Omdat die versameling van geleedpotige diere gewoonlik baie moeite vereis is ‘n maksimum steekproef gedoen by ‘n enkele lokaliteit. Daar is gevind dat ‘n verdubbling van die aantal ruitsteekproefnemings met vanggate meer effektief is om miere te vang as ‘n verdubbling in die tydperiode wat vanggate oop is. Dus, is ‘n hoër ruimtelike steekproef intensiteit meer effektief in vergelyking met ‘n langer tydsduur vir miere in die CFR. Die seisoenale veranderinge van grond-lewende geleedpotiges, sowel as miere, was ook bepaal. Dit was gedoen deur vier seisoenale steekproewe te doen by ‘n enkele lokaliteit. Die totale geleedpotige-talrykheid was die meeste gedurende die somer en die minste in die winter. Die miertalrykheid het ook hierdie patroon weerspieël. Dit dui daarop dat veranderinge in mier versamelings van breër belang is vir alle grondlewende geleedpotiges. Miere was die dominante grond-lewende geleedpotiges en beklemtoon die belangrikheid van miere in die CFR, sowel as hulle toepaslikheid as vlagskip taksa vir grond-lewende geleedpotige diversiteit in die CFR. Laastens was die bydrae van gefragmenteerde natuurlike veld in menslik–beinvloede gebiede tot die bewaring van die CFR ondersoek. ’n Krimpende/ genestelde hiërargies benadering is gebruik in vyf geselekteerde lokaliteite, elk het bestaan uit ‘n area in ‘n natuur reservaat en ‘n area in ‘n naasliggende fragment. Miere was versamel saam met ‘n verskeidenheid omgewings veranderlike, naamlik weer, plantegroei en grond. In die algemeen is gevind dat fragmente en reservate gelyksoortige mier versamelings het. Daar was wel gevind dat party fragmente aansienlik verskillend was van die reservaat teenstuk. Verskille in mier versamelings tussen lokaliteite was groter as verskille tussen reservate en fragmente. Die relatief hoë heterogeniteit van miere beklemtoon die bewaringsbelang van invertebrate saam met dié van plante in die CFR. Dit is duidelik dat fragmente wel ‘n potensiale bydrae kan maak om die mier versamelinge te bewaar, maar gepaste bestuur is nodig om hierdie potentiaal te maksimaliseer. Versteurings soos die teenwoordigheid van die indringer Argentynse mier en toenemende grondvoedingstofkonsentrasie as gevolg van bemesting is ‘n groot bedreiging tot die vermoë van fragmente om mier versamelings te bewaar. Hierdie studie wys dat mier versamelings in gefragmenterde areas verteenwordigend is van die algemene mier versamlings wat op die oomblik in die CFR is. Dus lewer party fragmente in landbou gebiede op die oomblik ‘n wesenlike bydrae tot die bewaring van ‘n funksioneel belangrike takson in hierdie globale biodiversiteitsbrandpunt en die bydra sal volhoubaar wees met korekte bestuur.

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