Species invasions on islands: searching for general patterns and principles

Numerous islands worldwide are being increasingly invaded by exotic species. However, the effects of invading species on native floras remain underexplored, particularly whether island biogeography theory is applicable to native, exotic, and the newly assembled floras. Inter-group comparisons across different regions or island groups through a collection of individual studies have the potential of offering additional insights. Here, I comparatively analyze 10 datasets involving bird and plant invasions on nine island groups around the world and make detailed comparisons between two sets. I show that, although similarities exist, different taxonomic groups and different geographic settings exhibit drastically different invasion patterns on islands. Island biogeography theory still better explains native and overall (natives plus exotics) diversity patterns, such as the species-area-isolation relationships. In contrast, the corresponding patterns for exotic species are highly variable. The varying degrees of human intervention in species invasion relative to natural dispersal on different islands, along with differences between taxonomic groups, highlight the challenges of searching general patterns and applying island biogeography theories to island invasion and conservation.