Species migrations and range shifts: A synthesis of causes and consequences

In increasingly changing environments, plant species are forced to either adapt to novel conditions or shift their ranges to track their ecological niches. Those species that can successfully track their niche may minimize extinction risks. However, establishment of new species into recipient communities will lead to species rearrangement and novel biotic interactions. Currently, we have a limited understanding of how these processes affect communities and ecosystems. In this review we synthesize current knowledge on range-expanding species. We start with addressing the many terms used for describing different aspects of range expansions, such as native-invasive, encroachers, and intra-continental invasive species. Thereafter, we describe the factors driving range expansions, and the effects on recipient communities and at the ecosystem level. Our research indicates that, similar to the study of biological invasions, current knowledge on range expansions is highly biased, with most of the studies focusing on Europe and North America. A large part of the available research targets trees and shrubs and the most investigated habitats are grasslands, savannas and high-elevation habitats. One potential consequence of such research bias is that range expansion of many herbaceous species (especially of those species not important for agriculture) may go undetected. Another important finding is that the same factor may promote or hinder range expansion depending on habitat, life form, spatial and temporal scale at which the process is studied. Finally, while many range expansions have negative consequences on local biodiversity and community stability, some of them have positive effects (e.g. mangroves). Although an increasing number of studies investigated the effects of range expansion on recipient communities, our research indicates that we still have a limited knowledge of such processes. Future efforts should integrate both empirical and modeling approaches to disentangle the joint effects of biotic, abiotic and anthropogenic factors on range expansion. Such research should focus both on the immediate-and longer-term implications of range expansions.