Living on the edge in species distribution models: The unexpected presence of three species of butterflies in a protected area in southern Spain

Abstract

MaxEnt (Maximum Entropy) modelling method is probably the most popular technique to model species distributions based only on the presence records across broad spatial scales. Although it is widely used, there is much controversy about the transferability of models between different geographical areas. Transferability might be more questionable when it comes to predict the distribution of peripheral populations at the margin of the species geographical range, where they may be affected by and adapted to environmental conditions different from those of core populations. To explore transferability of MaxEnt models among sectors of the geographic range, we selected three butterfly species with wide distributions and peripheral populations at their southernmost margin in the Iberian Peninsula, namely Plebejus argus, Cyaniris semiargus and Pyronia tithonus.Using data from the Atlas of the butterflies of the Iberian Peninsula and Balearic Islands as well as both climate and land use data, we modelled their potential distribution ranges in Spain. In addition, we also independently modelled their distributions separately in three concentric sectors of their range. We then investigated the transferability of the models between sectors and the effect of varying the regularization parameter.Our results show that when developing species distribution models the quality of occurrence data should be carefully checked, paying special attention to both their number and spatial distribution and avoiding possible significant biases.The transferability of the models tends to decrease when data from increasingly distant sectors are used as test data. More precisely, and independently of the regularization parameter value, models built using occurrence data either from the core or the intermediate sectors failed to adequately predict the distribution of the three butterfly species in the peripheral sector, especially in Doñana National Park.