How regional transport networks shape non-native plant distributions across isolated South Pacific islands: the case of French Polynesia

Résumé fourni par la source

Pacific Island ecosystems are particularly vulnerable to plant invasions due to their ecological isolation and high endemism. In a global study (van Kleunen 2015), the Pacific Islands exhibited the highest accumulation rate of naturalised plant species relative to their area. However, invasion processes across these islands are incompletely understood, particularly from a metacommunity perspective. Most ecological studies focus on individual islands, while research on human-mediated transport is typically global in scope, and the role of inter-island transport is understudied. Using French Polynesia as a study system, we compare drivers of species turnover between native and non-native plants to better understand invasion mechanisms, in particular the role of regional transport networks. Native species composition across islands is considered a baseline to which patterns of non-native species composition can be compared. We built a custom database of species-island records for French Polynesia from multiple databases: Nadeaud (Chevillotte et al. 2019), GBIF.org (2025), GIFT (Weigelt et al. 2019) and PaciFLora (Wohlwend 2021). Species native status was verified by cross-referencing regional checklists (Fourdrigniez and Meyer 2008; Wagner and Lorence 2002), PaciFLora (Wohlwend 2021), and POWO (2026), along with local expertise (1315 native; 1032 non-native; 575 non-native outside cultivation). Of the 97 islands in the database, 23 met inclusion criteria for analysis. To quantify human-mediated connectivity, we developed a multi-layer network integrating geographical distance, inter-island flight frequencies calculated from airline schedules (Air Tahiti 2018), and shipping route data (Direction Polynésienne des Affaires Maritimes 2019). Generalised dissimilarity models (Ferrier et al. 2007) were used to evaluate the relative contributions of climate, distance and human-mediated connectivity to species turnover of native and non-native plants (cultivated species excluded). Generalised dissimilarity models of native species explained more variation in turnover than for non-native species, reflecting the role of environmental filtering in shaping native species distributions over long timescales. Incorporating human-mediated connectivity nonetheless substantially improved models of non-native species turnover compared to models using geographical distance (explained deviance increased by 11 percentage points, ΔAIC>7). These results demonstrate and quantify the role of regional transport networks for the spread of non-native plants, highlighting the need for stronger inter-island biosecurity.

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