The impacts of invasive plants on springtail diversity on sub-Antarctic Marion island

Kgopong, Rashawe Modiwa (2019-03)

Thesis (MSc)--Stellenbosch University, 2019.

Thesis

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.

AFRIKAANSE OPSOMMING: Indringerspesies is doelbewus asook onbewustelik wêreldwyd – in beide vastelandasook geïsoleerde eilandekosisteme – versprei, met die mees skadelike effekte wat op eilande as gevolg van hul isolasie en hoë endemisme van spesies plaasvind. Verskeie sub-Antarktiese eilande is deur plante, diere en insekte, meestal van Europese oorsprong, ingedring. Marion-eiland vorm deel van die Prins Edwardeilande en is oor tyd deur verskeie spesies ingedring. Vaatplante, hoofsaaklik in die Poaceae, Caryophyllaceae en Juncaceae families uit Europa, het suksesvol op die eiland weens hul breë omgewingsverdraagsaamheid gevestig en het daarin geslaag om die meerderheid van die ses habitat-gemeenskapskomplekse op Marion-eiland te oorheers. Springsterte wat op Marion-eiland aangetref word, bewoon al ses habitatkomplekse, waar hulle een van die vollopste ongewerweldes is. In hierdie studie het ek die invloed van plantegroei op die verspreiding en vollopheid van springstertspesies op Marion-eiland spesifiek ondersoek. Ek het bevind dat springsterte op Marion-eiland met beide indringer- en inheemse plantegroei geassosieer word, met indringerspringsterte wat habitatte in laerliggende kusareas verkies waar inheemse Poa cookii en Cotula plumosa, asook die indringers Poa annua, Agrostis stolonifera en Sagina procumbens oorheers. Hierdie kusplantegroei word egter deur die teenwoordigheid en vollopheid van indringerspringsterte soos Isotomurus maculatus en Ceratophysella denticulate oorheers. Ceratophysella denticulata kom in baie hoë vollopheid voor waar dit teenwoordig is en dus kon hierdie spesie moontlik inheemse springsterte verplaas het – soos waargeneem in Hypogastrura viatica wat ‘n indringer op ander subAntarktiese eilande is. Verder kan C. denticulata potensieel inheemse spesierykheid op hierdie eilande verminder. Terwyl die meeste indringerspringsterte warmer kushabitatte verkies, is Pogonognathellus flavescens en Megalothorax minimus in hoërliggende habitatte gevind. Die teenwoordigheid van P. flavescens op hierdie hoogtes is verrassend, aangesien hierdie spesie voorheen slegs in 'n paar kusareas gevind is. Uit die resultate is dit duidelik dat beide inheemse en indringerspringsterte sterk op hoogte bo seespieël reageer. Die toename in hoogte lei tot verlaagde springstert vollopheid en spesierykheid, ongeag of die spesie inheems of ‘n indringer is. ‘n Hoofkoördinaat-analise het getoon dat ses uit die nege inheemse springstertspesies op die eiland in koeler, middelhoogte habitatte gevind word, met die uitsondering van Folsomotoma marionensis, Mucrosomia caeca en Cryptopygus dubius wat laerliggende habitatte verkies. Ander inheemse spesies soos Cryptopygus antarcticus travei en Tullbergia bisetosa het die meeste in klam komplekse, byvoorbeeld naby riviere en moerasse wat op middelhoogtes geleë is, voorgekom. Die seldsame inheemse springstertspesies kan die risiko loop om uit te sterf, weens hul huidige lae getalle wat verder kan afneem namate habitatte deur indringerplantegroei en klimaatsverandering gewysig word. Met toenemende klimaatsopwarming is dit moontlik dat hierdie veranderinge spesifieke indringerspesies kan bevorder, aangesien hulle droë en warmer toestande beter as inheemse spesies kan verduur. Daarbenewens is die toename in die verspreiding van indringerplantegroei soos C. fontanum, S. procumbens en kuslangse A. stolonifera na hoërliggende areas van groot kommer, aangesien hierdie spesies 'n afname in inheemse plantegroei kan veroorsaak wat in wese die habitat van inheemse springsterte is. Groot areas van indringerplante is reeds oor die hoogtegradiënt teenwoordig, met die effek daarvan op inheemse springsterte wat deur die aanwesigheid van indringerplante op die eiland vererger word. Die impak van indringerspringsterte op inheemse spesies word nog nie volkome verstaan nie en moet eksperimenteel getoets word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105612
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