The potential of ecoregional range maps for boosting taxonomic coverage in ecology and conservation

Expert range maps (ExpRMs) are frequently used to inform species distributions, but often incomplete or missing for many species, particularly among plants and invertebrates. Many species without ExpRMs also have too few occurrence records for reliable application of species distribution models (SDMs). Here we evaluate the performance of commonly used range surrogates and recommend tools that can help fill this significant knowledge gap across a wide range of understudied taxa. Specifically, we explore an alternative range surrogate (ecoregional range maps; EcoRMs), assess its performance versus traditional approaches for 624 North American butterfly species, and outline its use alone and as part of SDMs. As an alternative range estimate, we use terrestrial ecoregions that represent a regionalization of biogeographical zones and we suggest geographical filters and simplifications that improve their performance. We show that consistently across different spatial scales and both in comparison with ExpRMs and SDMs, EcoRMs have an exceptionally high sensitivity and generally a high mean performance. Particularly for species with fewer than 100 occurrence records, EcoRMs outperform other range surrogates. The congruence of species richness patterns was also similar for all approaches. The use of EcoRMs as substitute for data-poor species without ExpRMs will strongly boost taxonomic coverage of range maps. Additionally, integrating EcoRMs as domains/masks/offsets into SDMs promises significant improvements to model accuracy. For butterflies alone, EcoRMs would thereby provide new range information for 17% and improve basic range information for 43% of all approximately nineteen thousand species. Other technical advantages of generating EcoRMs may also help to overcome issues of the availability, updateability, reproducibility, and circularity of ExpRMs, SDMs and minimum convex hulls (MCVs). In summary, ecoregion-based range maps offer a versatile tool for ecology and conservation of terrestrial taxa and the application of the EcoRM approach may prove similarly useful for freshwater and marine ecoregions.

Automated summary

This study evaluates the performance of range surrogates and recommends methods for filling knowledge gaps in species range maps. The study explores an alternative range surrogate for North American butterfly species and demonstrates its high sensitivity and performance, particularly for species with few occurrence records.