New publication: ExDet, an EXtrapolation DETection tool for the modelling of species distributions

ExDet: Here be dragonsIntroducing the ExDet tool

Correlative species distribution models (SDMs) often involve some degree of projection into novel covariate space. Most methods for identifying this extrapolation focus on the range of each model covariate individually. However, extrapolation can occur that is well within the range of univariate variation but which exhibits novel combinations between covariates. It is, therefore, important that we develop a better understanding of dragons potentially lurking in the uncharted waters of novel covariate space.

The ExDet tool, based on the Mahalanobis distance, is a free standalone software package with multiple features:

  • measures the similarity between reference and projection domains by accounting for both the deviation from the mean and the correlation between variables
  • provides metrics and maps of Type 1 and Type 2 novelty
  • provides an assessment of the most influential variables leading to dissimilarity
  • provides graphical tools for improved interrogation and understanding of covariate data

The ExDet tool is robust and insightful quantitative method for exploring novelty for and interpreting projections from correlative SDMs. The tool is available for free download as a standalone software package and is described in full in the following paper:

ExDet: Here be dragons• Mesgaran, M.B., Cousens, R.D. & Webber, B.L. (2014) Here be dragons: a tool for quantifying novelty due to covariate range and correlation change when projecting species distribution models. Diversity & Distributions, 20: 1147–1159. [Download]