Full dataset for paper: Positive feed-back between invasive species in a Sub-Antarctic ecosystem: a case of invasional meltdown?

Invasional meltdown, where interactions between non-native species amplify their ecological impacts, is often evidenced through weaker cases involving direct benefits of one invader to another. However, stronger versions involving reciprocal effects remain poorly explored, particularly in extreme environments. This study explores inter-trophic facilitation, encompassing direct and indirect effects, on a sub-Antarctic island, an ecosystem of high conservation value traditionally considered resistant to invasions. We hypothesised that the invasive grass <i>Poa annua</i> directly enhances the performance of the invasive predatory beetle <i>Trechisibus antarcticus</i> by improving microclimatic conditions, increasing food availability, and reducing physiological stress on South Georgia Island. Additionally, <i>T. antarcticus</i> preys on the native herbivore <i>Hydromedion sparsutum</i>, whose larvae preferentially feed on <i>P. annua</i>, suggesting a potential positive feedback loop reinforcing <i>P. annua</i>’s invasion. Our findings reveal that <i>P. annua</i> increases the abundance, weight, size, and physiological performance of <i>T. antarcticus</i>, ameliorates environmental stress, and provides more food than native vegetation and bare soil. This direct facilitation represents a critical mechanistic link supporting a strong version of invasional meltdown. This study presents the first documented case of invasional meltdown in an Antarctic ecosystem, highlighting the potential for cascading inter-trophic interactions to drive invasion success in ecologically sensitive and climatically challenging ecosystems.