Study area
The Prince Edward Islands (PEIs) consist of Marion Island (46° 54’ S, 37° 45’ E; area: c . 270 km2) and the smaller Prince Edward Island (46° 38’ S, 37° 57’ E area: c . 45 km2), which are located in the Southern Indian Ocean. The islands are of volcanic origin, and are believed to be approximately half a million years old (Chown and Froneman, 2008). Marion Island, the higher of the two islands, reaches an altitude of 1230 m (Chown and Froneman, 2008). The PEIs are home to a considerable population of globally threatened seabird species, and several plant and insect species (Crawford et al., 2003, Jones and Ryan, 2010, Chown and Convey, 2016, Chau et al., 2020). The islands have two major biomes: the sub-Antarctic tundra, located in lowland areas, and sub-Antarctic polar desert, which lacks vascular plants and is limited to higher elevations (Smith and Mucina, 2006). The tundra vegetation has been broadly divided into three mapping units: Coastal Zone, Inland Vegetation and Fellfield Vegetation (van der Merwe et al., 2023).
The PEIs have an oceanic climate with average annual temperatures of approximately 6.5°C, annual precipitation of around 2000 mm, high humidity and strong winds (Chown and Froneman, 2008). Climatic conditions on the islands are changing rapidly in step with global climate change, with temperatures having increased by 1.2°C and precipitation decreased by 25% since the 1960s (le Roux and McGeoch, 2008, Smith, 2002). Additionally, invasion by some plant and animal species is transforming some of these islands’ landscapes, especially on the more heavily impacted Marion Island (Gremmen et al., 1998, McGeoch et al., 2015, Houghton et al., 2019). Biologically, the PEIs constitute a fairly simple system, with few vascular plant species (around 22 native and 6 persistent invasive aliens) (Chau et al., 2020, Greve et al., 2017). Because of these factors, as well as the island’s isolation, Marion Island is a good model system for studying various ecological processes.