An aggressive invasive, Sagina procumbens, causes a partial invasional-meltdown on sub-Antarctic Marion Island

Abstract

Invasional meltdown occurs when one invasive species facilitates other invasives’ establishment, spread and abundance, and subsequently increases their impacts. Most studies on invasional meltdown have assessed facilitation of one invasive species by another invader, or of one invader on other invaders on one taxon, but few have assessed meltdowns in different taxa. Therefore, the aim of this study was to assess whether an invader causes invasional meltdowns in two very different taxa. Sagina procumbens (Caryophyllaceae. is an invasive cushion- or mat-forming vascular plant that has spread extensively on sub-Antarctic Marion Island. Little is known about its impacts, though observations suggest that it could be negatively impacting biodiversity and ecosystem functioning on the island. Therefore, we assessed whether S. procumbens is facilitating invasional meltdown of plant and collembolan communities on Marion Island. The abundance, richness, and species composition of native and invasive vascular plants growing on, and of native and invasive collembolans living in, S. procumbens were compared to those of two indigenous plant species (Azorella selago and Clasmatocolea humilus. which are being locally outcompeted by S. procumbens. Neither native nor invasive richness nor composition of the plants growing on S. procumbens differed significantly to that of plants growing on the two native control species. The richness of invasive collembolans was significantly higher in S. procumbens compared to the native control species; however, the richness of native collembolans in S. procumbens were not significantly different to that in A. selago and C. humilis. The abundance of invasive collembolans was significantly higher in S. procumbens compared to the native control species; a similar trend was found for native collembolans. The composition of invasive and native collembolans was significantly different between the three focal plant species. Therefore, we show evidence of an invasional-meltdown in collembolans, but not vascular plants, facilitated by S. procumbens. - Abstract as displayed in the - Abstract booklet. The presentation on the day may differ from the - Abstract.