Extinction dynamics of endemic trees in exotic-dominated ecosystems – EDENE

Regional species assemblages have been shaped by colonization, speciation and extinction over millions of years. During the last centuries, humans have dissolved natural biogeographic barriers. The introduction of alien invasive species (IAS) and subsequent loss of native (often endemic) species is causing the breakdown of regional distinctiveness of the Earth’s biota, a process called ‘biotic homogenization’ (BH). The mode of action of IAS has fuelled several well-established hypotheses referring to three levels of biological organization: 1) species level: hypotheses of vacant niche and competitive exclusion, 2) community level: mutualism disruption, invasional meltdown and novel biochemical weapons, 3) ecosystem level: concept of ecosystem engineers, which alter disturbance regime, succession and productivity. These hypotheses have however seldom been evaluated in natura using threatened native species, which makes it difficult to identify which ecological mechanisms prevail in causing BH. Our project aims to fill this gap by asking two questions: Q1) through which processes do IAS act? Q2) Do these processes change along the species extinction trajectory i.e. the decline of threatened species? These questions will be addressed by combining: 1) plot inventories set up around populations of at least 40 threatened woody plants endemic to the Mascarenes islands and botanised > 10 years ago, 2) joint species distribution models, a fast-developing method for analysing community data, supplemented by experiments under controlled conditions, 3) remote sensing analyses of major ecosystem shifts and exogenous disturbances that occurred during the last > 50 years over inventoried populations. The complementary nature of biological measurements and their nested scales will reveal what type of pressure IAS exert on VU, EN and CR endemic species, thus allowing targeting the ultimate mechanisms of BH in local conservation efforts and upcoming international agendas.