Invasive species risk assessments need more consistent spatial abundance data

Bradley, B. A., Allen, J. M., O'Neill, M. W., Wallace, R. D., Bargeron, C. T., Richburg, J. A., & Stinson, K. (2018). Invasive species risk assessments need more consistent spatial abundance data. Ecosphere, 9(7), e02302. PDF.

Summary

When creating risk assessments of range-shifting invasive species, most spatial models focus on presence-only data.  Presence data are widely available for spatial modeling from museum records and GPS locations compiled by managers, scientists, and public participants (e.g., records uploaded to EDDMapS). But, presence is only one aspect of understanding overall impact.  In order to improve spatial risk assessments, spatial abundance information are needed.  Geographic regions where a species could achieve high abundance are of greater risk than areas where the species is more likely to remain at low abundance.  Bradley et al. (2018) assessed abundance information within the Early Detection and Distribution Mapping System (EDDMapS) and developed recommendations about how abundance data could be collected to better inform spatial risk assessments.  For plants, abundance data were most often collected as percent cover in binned categories (e.g., <1%, 1-5%, 5-25%, >25%).  Binned categories are easier to estimate and enter, and remain highly valuable for spatial analysis.  However, most cover estimates were not accompanied by an estimate of infested area (and vice versa).  GPS locations coupled with both an estimate of cover as well as an estimate of infested area provide the most useful and interpretable information for spatial risk assessments.

Take home points

  • Collecting abundance information in standardized formats across agencies and regions makes it much easier for researchers to access and interpret this valuable information.

  • Reporting both percent cover and estimated infested area provides the best information about abundance.

  • Reporting absence of species combined with surveyed area also provides valuable information for spatial analysis.

Management implications

Managers are doing an outstanding job of documenting spatial occurrence data for invasive species and reporting this information to EDDMapS or iMap Invasives.  Adding estimates of abundance would enable improved spatial modeling of invasion risk by identifying areas with potential for abundant infestations. 

Keywords

Range Expansion; Invasive Plant; Risk Assessment