The response of biological communities to natural and anthropogenic habitat fragmentation in South Outeniqua Sandstone Fynbos, South Africa

Autor: Sandberg, Rory Nimmo
Rok vydání: 2013
Předmět:
Druh dokumentu: Diplomová práce
Popis: Thesis (MSc)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Habitat fragmentation through the loss and modification of natural ecosystems poses a serious threat to biodiversity globally. Mechanisms and ecological implications of fragmentation have been extensively studied, yet new and meaningful insights continue to be produced. The highly diverse and ecologically complex fynbos shrubland communities that occur in the Cape Floristic Region of South Africa are amongst the most threatened by habitat fragmentation by urban, agricultural and silvicultural land uses and to the spread of invasive alien plants. Fynbos vegetation communities are fire-adapted and exploit the post-fire regeneration niche. Natural stochasticity in the fire regime means that these communities are temporally unstable; a factor that allows for the coexistence of such extreme diversity. Few studies have attempted to assess the influence of habitat fragmentation on this stochasticity, or to investigate the response of biological communities to the conditions that result. It is unknown whether this temporal instability will lead to delayed extinctions in fragmented communities, thus generating extinction debt. South Outeniqua Sandstone Fynbos occurs as a unique landscape mosaic of both insular and extensive habitats, suited to study through an island biogeography framework. Vegetation community stability was assessed through the comparison of historic and recent data sets. The responses of local vegetation and avifaunal communities to habitat fragmentation were assessed and compared on the basis of their differing motility. The unique habitat configurations also allowed for the investigation of extinction debt in the local communities and provided an opportunity to assess the influence of the surrounding matrix on species persistence and on connectivity in the artificial fragments. Data were analysed through simple regression analyses, modified Chi-squared tests and through ordination analyses. Ultimately the value of the artificial habitat fragments for the conservation of biological communities was assessed. Stability was observed in the vegetation species-area relationship for the natural islands and the mainland sites over twenty-two years. Smaller islands were found to receive fewer fires than large islands and the mainland. This consistently over-extended fire-return interval reduces the stochasticity of the local fire regime causing stable yet depauperate vegetation communities to result. Vegetation communities in the artificial fragments were found to hold area-related extinction debt, possibly due to the relatively long-term demographic turnover that typically occurs in fynbos. Avifaunal communities varied in their response to fragmentation relative to the vegetation. Birds – being motile – were found to be unaffected by isolation distance or surrounding matrix type – their response due more to changes experienced in the vegetation community than to geographic constraints. Fynbos-typical birds responded to the post-fire age of vegetation. Frugivorous birds and the matrix-habitat edge were identified as sources of alien and non-fynbos plant species that colonise the artificial fragments, potentially reducing the quality of these habitats for avifauna. Fragmented communities of South Outeniqua Sandstone Fynbos have the potential to function as biological reserves. This potential can be realised through the implementation of a fire regime that acknowledges the stochasticity required by the vegetation, the frequency required by the vegetation and the avifauna, and the practicality required by surrounding anthropogenic land-uses.
AFRIKAANSE OPSOMMING: Habitat-fragmentering, deur die verlies en verandering van natuurlike ekosisteme, hou 'n ernstige bedreiging in vir biodiversiteit wêreldwyd. Meganismes en ekologiese implikasies van die fragmentering is al breedvoerig bestudeer, maar nuwe en betekenisvolle insigte word voortaan vervaardig. Die hoogs diverse en ekologies komplekse fynbos-struikveld gemeenskappe wat in die Kaapse Floristiese Streek van Suid-Afrika voorkom, word meeste bedreig deur habitat-fragmentering deur verstedeliking, landbou en houtteeltkundige grondgebruike en die verspreiding van indringerplante. Fynbos gemeenskappe is aangepas tot vuur en die uitbuiting van post- vuur herlewing nis. Natuurlike stogastisiteit in die vuur-bedeling beteken dat hierdie gemeenskappe tydelik onstabiel word, 'n faktor wat die mede-bestaan van uiterste diversiteit moontlik maak. Min studies het al die invloed van habitat-fragmentering op hierdie stogastisiteit ondersoek, of die reaksie van biologiese-gemeenskappe tot die voortspruitende omstandighede. Dit is onbekend of die tydelike onstabiliteit sal lei tot vertraagde uitsterwing in gefragmenteerde gemeenskappe, dus genereer uitsterwings-skuld. Suid Outeniqua Sandsteen Fynbos kom as 'n unieke landskap mosaïek van beide die eilande en uitgebreide habitatte voor, geskik om deur 'n eiland biogeografie raamwerk bestudeer te word. Plant-gemeenskappe se stabiliteit is bestudeer deur die vergelyking van historiese en onlangse data stelle. Die reaksies van die plaaslike plantegroei en voëllewe gemeenskappe tot hul habitat is bestudeer en vergelyk op grond van hul verskillende beweeglikheid. Die unieke habitat konfigurasies het ook toegelaat vir die ondersoek van uitsterwings-skuld in die plaaslike gemeenskappe en 'n geleentheid gebied om die invloed van die omliggende habitat-matriks op spesies volharding en op konneksie in die kunsmatige fragmente te bepaal. Die data is ontleed deur middel van eenvoudige regressie analises, aangepasde Chi -kwadraat toetse en deur koördinerings ontledings. Ten einde die waarde van die kunsmatige habitat fragmente vir die bewaring van biologiese gemeenskappe te bepaal. Stabiliteit in die plantspesies-area verhouding vir die natuurlike eilande en die vasteland van webwerwe oor twee en twintig jaar was waargeneem. Kleiner eilande het minder brande aangeneem as groot eilande en die vasteland. Hierdie herhaalde oor-uitbrei over-extended vuur-interval het die stogastisiteit verminder van die plaaslike vuur-bedeling wat stabiele tog spesie-arme plantegroei gemeenskappe veroorsaak het. Plantegroei gemeenskappe in die kunsmatige fragmente is bevind om spesie- area -verhouding uitsterwings-skuld te bevat, moontlik as gevolg van die relatiewe lang termyn demografiese omset wat tipies voorkom in fynbos. Voëllewe gemeenskappe het gewissel in hul reaksie tot die fragmentering relatief tot die plantegroei. Voëls – weens hul beweeglikheid – blyk om nie beinvloed te word deur isolasie afstand of omliggende habitat-matriks tipe nie - hul reaksie blyk meer asgevolg van veranderinge wat ervaar word in die plantegroei gemeenskap as geografiese beperkinge. Fynbos-tipiese voëls reageer op die post- vuur ouderdom van plantegroei. Vrugte-etende voëls en die habitat-matriks rand is geïdentifiseer as bronne van uitheemse en nie-fynbos plantspesies wat die kunsmatige fragmente koloniseer, wat potensieel die kwaliteit van hierdie habitatte vir voëls verminder. Gefragmenteerde gemeenskappe van Suid Outeniqua Sandsteen Fynbos het die potensiaal om as biologiese reserwes te funksioneer. Hierdie potensiaal kan verwesenlik word deur die implementering van 'n vuur-bedeling wat erkenning verleen aan die stogastiesiteit vereis deur die plantegroei, die frekwensie wat deur die plantegroei en die voëllewe vereis word, en die praktiese vereistes van die omliggende menslike grondgebruike.
Databáze: Networked Digital Library of Theses & Dissertations
Externí odkaz: