Current and modeled species distributions reveal global bias in species richness knowledge and invasion risk

Background/Question/Methods

Species distribution models can be used to understand species’ range limits as well as manage the spread of invasive species under current and future conditions. To date, numerous studies have used these models to predict species distributions, and several approaches have been developed. In addition, the availability of species’ presence data has increased, often in the form of open access data repositories. However, little research to date has focused on modeling global patterns in species richness and invasion risk. Here we utilize open access data (Global Biodiversity Information Facility) and a freely available species habitat modeling software (Maxent) to identify richness patterns for current and potential distributions for 31 ascidian (Phylum Chordata, Class Ascidiacea) species globally. We describe current distribution based on documented presence records and model potential distribution using several environmental parameters. By contrasting current and potential distribution for these species, we identify regions with differences between documented species richness and potential richness based on suitable habitat. These regions represent hot and cold spots for either identifying new invaders or for documenting future invasions, which could inform management strategies to help prevent new invasions from occurring.

Results/Conclusions

Current distribution patterns show a clear bias towards higher richness in temperate regions. In addition, these regions are often already settled by most, if not all, species that are modeled to have suitable habitat in these locations. Conversely, richness based on modeled potential distribution is highest in tropical areas. Many tropical regions, especially in and around the Tropical Western Pacific, contain suitable habitat for more species than are documented at present. These suitable but currently ‘under-invaded’ regions represent areas that may be at risk for future invasions if species that are predicted to survive there are introduced. Alternatively, these regions may be understudied and invaded by more species than currently documented. If this is the case, these results highlight regions that could benefit from further study and data collection. Based on either result, utilizing open access data and species distribution modeling provides for the identification of regions that warrant further consideration for research and potential management. Changes in global commercial trade patterns, which are associated with the transport of invaders, and future climate change, which can shift species distributions, have the potential to significantly alter where species have the highest potential for invading and deserve further study.