Print PageBiological invasions are a major threat to biodiversity, especially on islands. Islands have been considered more prompt to invasion than mainland due to their ecological singularities. However, recent studies suggest that differences may depend on the interaction with environmental and history factors such as differences in propagule pressure, human factors or habitat heterogeneity. We compared the level of plant invasion in coastal habitat types between Menorca island and Catalonia mainland (NE Spain). Four habitat types encompassing a gradient of human influence were sampled: forests, scrublands, dunes and cliffs. Alien plant richness at patch level was compared between island and continent, between habitat types and related to climate and landscape variables by variance partitioning methods.
Results/Conclusions
131 alien species were registered in Catalonia while only 27 in Menorca. The mean alien species richness at patch level was also higher in Catalonia (S=5.04) than in Menorca (S=0.53). The four coastal habitats in the island had similar degree of invasion whilst in the mainland, forests and scrublands had significant higher level of invasion than dunes and cliffs. Variance partitioning of alien plant richness revealed that landscape variables had similar effects than habitat type and insularity. In contrast, climate variables were less important. Alien plant richness was negatively related to percentage of natural vegetation and positively to percentage of built-up area in the landscape. Overall, our results suggest that islands are not always more invaded than their mainland counterparts and that the differences in the degree of invasion could be due to variation in human influence and landscape heterogeneity. These findings are critical for the management of plant invasion in coastal habitats because they imply that invasion at the local scale is influenced by the characteristics of the highly anthropic coastal landscape.
