Browsing by Author "Kgopong, Rashawe Modiwa"
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- ItemThe impacts of invasive plants on springtail diversity on sub-Antarctic Marion island(Stellenbosch : Stellenbosch University, 2019-03) Kgopong, Rashawe Modiwa; Wossler, Theresa; Chown, Steven; Janion-Scheepers, Charlene; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Invasive species have been intentionally and accidentally introduced globally to both mainland and isolated island ecosystems, with the effects more harmful on islands given their isolation and high endemism of species. Several sub-Antarctic islands have been invaded by plants, animals and insects, mostly of European origin. Marion Island forms part of the Prince Edward Islands and has been invaded by species over time. Vascular plants, mainly from the families Poaceae, Caryophyllaceae and Juncaceae from Europe, have successfully established on the island due to their broad environmental tolerance and have managed to dominate most of the six habitat community complexes on Marion Island. Springtails found on Marion Island occupy all of the six habitat complexes, where they are amongst the most abundant invertebrates. In this study, I investigated the influence of vegetation on the distribution and abundance of springtail species on Marion Island specifically. I found that springtails on Marion Island are associated with both invasive and native vegetation, with invasive springtails preferring habitats in lower lying coastal sites where native Poa cookii and Cotula plumosa, and invasive Poa annua, Agrostis stolonifera and Sagina procumbens dominate. However, this coastal vegetation was dominated by the presence and abundance of invasive springtail species such as Isotomurus maculatus and Ceratophysella denticulata. Ceratophysella denticulata occurs in very high abundance when present, thus this species may have displaced native springtails, such as observed for Hypogastrura viatica, which is invasive on other sub-Antarctic islands. Furthermore, C. denticulata may potentially reduce native species richness on these islands. While most invasive springtails prefer warmer coastal habitats, Pogonognathellus flavescens and Megalothorax minimus were found in higher altitudinal habitat. The presence of P. flavescens at this higher altitude is surprising, as this species was previously only found at a few coastal sites. From the results, it is clear that both native and invasive springtails respond strongly to altitude. The increase in altitude results in decreased springtail abundance and richness irrespective of whether the species is native or invasive. Principal coordinates analysis showed that six out of the nine native springtail species on the island are found in cooler, mid-altitude habitats with the exception of Folsomotoma marionensis, Mucrosomia caeca and Cryptopygus dubius which prefer lower lying habitats. Other native species such as Cryptopygus antarcticus travei and Tullbergia bisetosa were found to be most abundant in moist complexes, for example near rivers and mires that are found in mid-altitude areas. The rare native springtail species could face the risk of becoming extinct due to their current low numbers, which may further decrease as habitats are transformed by invasive vegetation and climate change. With increased climatic warming, it is possible that this change could favour particular invasive species as they can tolerate dry and warmer conditions better than native species. In addition, the increase in altitudinal distribution of invasive vegetation, such as C. fontanum, S. procumbens and coastal A. stolonifera, is of great concern as these species may cause a decline in native vegetation which is essentially habitat to native springtails. Large stands of invasive plants are already present along the altitudinal gradient with their effects on native springtails further exacerbated by the presence of invasive springtail species on the island. The impact of invasive springtails on native species is poorly understood, and should be experimentally tested.