Biodiversity conservation in a fragmented landscape : arthropod assemblages in smaller corridors within a production landscape

van Schalkwyk, Julia (2015-04)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: Habitat loss and fragmentation are major threats to global biodiversity. A cornerstone of traditional conservation involves setting aside land as formally protected areas (PAs). However, for effective biological conservation in the long term there needs to be connectivity between these PAs. When possible, improved connectivity can be achieved using natural corridors at a landscape scale. Even better is to establish a network of corridors and nodes in the form of ecological networks (ENs). ENs are currently being employed by commercial forestry companies in South Africa. While larger corridors and nodes are considered optimum, factors other than design, such as management and environmental heterogeneity, have also been found to be important for species maintenance. This study aims to explore the role of corridor width in driving the composition of invertebrate assemblages across a transformed landscape in KwaZulu-Natal, South Africa, and to investigate other possible environmental variables significant for species distributions. In Chapter 2, I investigated the contribution of smaller grassland corridors within a timber production matrix to overall biodiversity conservation using two important bioindicator taxa. Ants and dung beetles were sampled in grassland corridors of three size classes, plantation blocks and a nearby PA, iMpendle Nature Reserve. The two taxa showed differential responses to landscape level fragmentation. Dung beetles showed a decrease in species richness and corresponding increase in species turnover with increased fragmentation, while ants were unaffected, although counter intuitively smaller corridors even contained more unique ant species compared to larger corridors. Dung beetle assemblages also showed strong differences between the PA and grassland corridors. While the conservation effectiveness of large corridors undoubtedly exceeds that of smaller corridors, for ants it seems that smaller corridors contribute to their overall conservation within this production landscape. In Chapter 3, I explore the importance of spatial and environmental factors for species distribution across this landscape. Dung beetles were split into functional guilds according to size and nesting behaviour for analyses. Within grassland corridors, tunnelling dung beetle species richness was sensitive to landscape level fragmentation, especially for larger species, while elevation and vegetation type influenced ant species richness. Since rolling dung beetles showed a close association with the PA, the marked difference in dung beetle assemblages between these two land-uses may be due to the presence of pellet producing grazers in the protected area and their replacement by pat producing cattle in the grassland corridors. Other environmental variables that were found to be important for dung beetle species composition were elevation, vegetation type, and soil hardness. For ant species composition, only elevation was found to be important. In conclusion, as large corridors were comparable to the PA in dung beetle and ant species richness, ENs act as extensions of formally PAs, given that they are large enough. Nevertheless, smaller corridors had surprisingly high species richness. Including additional information other than species data improved our knowledge of the underlying factors that drive dung beetle species composition. Even though dung beetle and ant species responded differentially to habitat fragmentation, environmental heterogeneity seemed important for both taxa. Incorporating habitat heterogeneity into the current management scheme may improve the conservation effectiveness within this transformed landscape.

AFRIKAANSE OPSOMMING: Die vermindering en fragmentasie van natuurlike habitat is ‘n groot bedreiging vir globale biodiversiteit. ‘n Belangrike tradisionele benadering tot natuurbewaring behels die afbakening van land vir formele beskermde areas (BAs). Ten einde effektiewe biologiese bewaring oor die langtermyn te verseker moet daar verbinding wees tussen hierdie BAs. Indien moontlik kan verbeterde verbinding verkry word deur die gebruik van natuurlike gange op ʼn landskaps-vlak. Nog beter is om ʼn netwerk van gange en nodes in die vorm van ekologies netwerke (ENe) saam te stel. ENe word tans deur kommersiële bosboumaatskappye in Suid Afrika aangewend. Terwyl groter gange en nodes as optimaal beskou word, is ander faktore behalwe ontwerp, soos bestuur en omgewingsheterogeniteit, ook al gevind as belangrik vir die onderhouding van spesies. Hierdie studie is gemik daarop om die rol van gangwydte as dryfkrag vir die samestelling van invertebraatversamelings oor ʼn getransformeerde landskap in KwaZulu-Natal, Suid-Afrika, te ondersoek, asook ander moontlike omgewingsveranderlikes wat belangrik vir spesiesverpreidings kan wees. In Hoofstuk 2 het ek die bydrae van kleiner gange tot totale biodiversiteit-bewaring ondersoek deur twee belangrike bio-indikator taxa te bestudeer. Miere en miskruiers is versamel in grasland-gange van drie grootte-klasse, plantasie blokke en ‘n naby geleë BA, iMpendle Natuurreservaat. Die twee taxa het verskillende reaksies tot landskaps-vlak fragmentasie getoon. Miskruiers het ‘n verlaging in spesiesrykheid en ‘n gesamentlike verhoging in spesiesomset met verhoogde fragmentasie gewys, terwyl miere nie geaffekteer is nie, alhoewel kleiner gange het trouens meer unieke mierspesies bevat as groter gange. Die miskruierversamelings in die BA het ook opmerklik verskil van dié in die grasland-gange. Alhoewel die bewaringsdoeltreffendheid van groot gange beslis dié van kleiner gange oorskry, kom dit voor dat kleiner gange wel bydra tot die totale bewaring van miere binne hierdie produksielandskap. In Hoofstuk 3 het ek die belangrikheid van ruimtelike en omgewingsfaktore vir spesiesverspreiding oor hierdie landskap ondersoek. Miskruiers is ook in funksionele groepe verdeel volgens grootte en nes-gedrag vir aparte analise. Binne grasland-gange was tonnellende miskruierspesies sensitief vir landskaps-vlak fragmentasie, veral groter spesies, terwyl hoogte bo seevlak en vegetasie tipe mier spesiesrykheid beïnvloed het. Aangesien rollende miskruierspesies ‘n nabye assosiasie met die BA gewys het, mag die opmerklike verskil in miskruier versamelings tussen hierdie twee grondgebruike ʼn gevolg wees van die aanwesigheid van korrel-mis produserend beweiders in die BA en hulle vervanging deur nat-mis produserende beeste in die grasland-gange. Omgewingsveranderlikes uitsluitende ganggrootte wat belangrik gevind is vir miskruier spesiessamestelling was hoogte bo seevlak, vegetasie tipe en grond-hardheid. Vir mier spesiessamestelling was slegs hoogte bo seevlak belangrik. Om af te sluit, aangesien groot gange vergelykbaar was met die BA in miskruier en mier spesiesrykheid, tree ENe op as uitbreidings van BAs, mits hulle groot genoeg is. Desnieteenstaande het kleiner gange ‘n verbasende hoë spesiesrykheid gehad, veral onder miere. Die insluiting van addisionele inligting buiten spesiesdata het ons kennis van die onderliggende faktore wat miskruier spesiessamestelling dryf verbeter. Alhoewel miskruier- en mierspesies verskillend gereageer het op habitat fragmentasie, het dit voorgekom asof omgewingsheterogeniteit belangrik was vir die spesiesverspreiding van beide taxa. Die insluiting van habitatheterogeniteit binne die huidige bestuursplan mag die doeltreffendheid van bewaring binne hierdie getransformeerde landskap verbeter.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/96752
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