The biogeography of alien plant invasions in the Mediterranean Basin

Abstract

Aims: Humans have deeply eroded biogeographic barriers, causing a rapid spread of alien species across biomes. The Mediterranean Basin is a biodiversity hotspot but is also known as a hub of alien plant invasions, particularly in its European part. Yet, a comprehensive inventory of alien species in the area is missing and understanding of the drivers of Mediterranean invasions is poor. Here, we aim to identify the main alien plant species in the European part of the Mediterranean Basin and quantify their invasion success in order to understand the plant species flows from other biomes of the world. Location:The Mediterranean region of Europe, Anatolia and Cyprus. Methods:We analyzed 130,000 georeferenced vegetation plots from the European Vegetation Archive (EVA) and identified 299 extra-European alien plant species. We identified their biomes of origin and quantified the mean geographic distance, trade exchange and climatic similarity from each biome to the study area. After estimating the invasion success of each species in the study area, we tested which biomes have donated more alien species than expected by chance and which drivers best explain these non-random patterns. Results:We found that other Mediterranean climatic regions, as well as temperate and xeric biomes of the world, are the main donors of successful alien species to Mediterranean Europe, beyond what would be expected by chance. Our results suggest that climatic matching, rather than geographic proximity or trade, has been the most important driver of invasion. However, climatic pre-adaptation alone also does not appear to predict the invasion success of established species in the study area. Conclusions:Our results highlight the need to pay special attention to alien plant species from the same or climatically similar biomes, but also suggest that further research is needed for early screening of the most problematic alien species.

Invasion success on European coastal dunes

“…However, we should note that the relationship between geographic origins and the invasion success of alien plants was not statistically significant. This result confirmed those of Cao Pinna et al (2020), focused on the Mediterranean part of Europe and remarks that invasion success is not predictable by the species origin at continental scale. A possible explanation could be that species origin is more related to propagule pressure, depending especially on distance and human trade (van Kleunen et al 2015;Seebens et al 2015Seebens et al , 2017Moser et al 2018), than our three components of invasion success.…”

“…However, these components are not always correlated and could be highly variable, making it sometimes difficult to unequivocally identify the most successful aliens. In this sense, other authors proposed to consider these three components together in order to quantify the invasion success (Carboni et al 2016;Cao Pinna et al 2020).…”

“…Different studies have highlighted the importance of life forms and geographical species origin as factors related to invasion success (van Kleunen et al 2015;Giulio et al 2020;Cao Pinna et al 2020). Life forms (Raunkiaer 1934) are among the most simple but informative ecological traits (Acosta et al 2006), defining species ecological strategies in an extremely synthetic way.…”

Invasion dynamics and potential future spread of sea spurge across Australia’s coastal dunes

“…Finally, during the invasion process, E. paralias has been exposed to similar environmental conditions as those encountered in the native range, the result of which is almost no abandonment and little pioneering. This confirms the general assumption that environmental similarity with the region of origin is a critical factor for successful invasions (Cao Pinna et al, 2020;Ficetola et al, 2007).…”

Neophyte invasions in European grasslands

“…Long-term presence on the continent and relatively short distances between European countries, as opposed to intercontinental distances, can cause neophytes of European origin to be on average more common in the secondary part of their European range than neophytes originating from outside Europe (Lambdon et al, 2008). For non-European neophytes, establishment success is influenced by the time since the introduction and the degree to which the invaded area in Europe resembles their native range, expressed by climate matching at a coarse scale (Thuiller et al, 2005;Cao Pinna et al, 2021). Since geographical patterns of neophyte invasions might considerably differ among broad vegetation types at the country level (Divíšek & Chytrý, 2018), we need to explore the patterns in grasslands and other vegetation types at the European level separately, rather than inferring them from the patterns found for the whole flora or other vegetation types.…”