The Sweet Spot: A Holistic Method of Taxonomically Adjusted Range Delineation for Global Unification

Wildlife conservation is an increasing necessity as well as a challenge, partially due to the absence of a consistent framework among countries. One of the basic needs for conservation planning is species range delineation, where a variety of methods are used for mapping species distributions, reflecting the variety in parties providing data as well as the tools and methods used to determine boundaries. So far, a unified method that can be adopted for all types of data and taxonomic units is absent. Here, we compare the advantages and drawbacks of the three main types of range delineation methods found in the literature: political, hand-drawn, and modelling boundaries. Further, we present a pragmatic and holistic method to determine a taxonomically adjusted minimum segment length, defined as the distance connecting any two vertices and which end-to-end alignment can be used for drawing ranges for all animal taxa, derived from the median of all species’ range area within a taxonomic unit. Our recommended minimum segment lengths vary from 1.13 km to 3.40 km (at the equator), with the value for most taxonomic groups being between two and three kilometers. Using two example species, we demonstrate the efficacy of our method in comparison to other methods in terms of sensitivity and unnecessary polygon complexity, and advocate for the combination of model outputs and expert knowledge using our recommended segment lengths. We encourage range maps to be drawn in consideration of known occurrence records and highlight the value of the continual collection of range data both from citizen science and targeted surveys. Overall, our recommendation guides conservation planners towards a unified method to delineate ranges that can be globally adopted.