The Use of Climatic Niches in Screening Procedures for Introduced Species to Evaluate Risk of Spread: A Case with the American Eastern Grey Squirrel

Mirko Di Febbraro,Heroen Verbruggen,Sandro Bertolino,Luigi Maiorano,Marco Girardello,Piero Genovesi,Peter W W Lurz

doi:10.1371/journal.pone.0066559

Abstract

Species introduction represents one of the most serious threats for biodiversity. The realized climatic niche of an invasive species can be used to predict its potential distribution in new areas, providing a basis for screening procedures in the compilation of black and white lists to prevent new introductions. We tested this assertion by modeling the realized climatic niche of the Eastern grey squirrel Sciurus carolinensis. Maxent was used to develop three models: one considering only records from the native range (NRM), a second including records from native and invasive range (NIRM), a third calibrated with invasive occurrences and projected in the native range (RCM). Niche conservatism was tested considering both a niche equivalency and a niche similarity test. NRM failed to predict suitable parts of the currently invaded range in Europe, while RCM underestimated the suitability in the native range. NIRM accurately predicted both the native and invasive range. The niche equivalency hypothesis was rejected due to a significant difference between the grey squirrel’s niche in native and invasive ranges. The niche similarity test yielded no significant results. Our analyses support the hypothesis of a shift in the species’ climatic niche in the area of introductions. Species Distribution Models (SDMs) appear to be a useful tool in the compilation of black lists, allowing identifying areas vulnerable to invasions. We advise caution in the use of SDMs based only on the native range of a species for the compilation of white lists for other geographic areas, due to the significant risk of underestimating its potential invasive range.

Highlights

Species introduction represent one of the main factors in the ongoing biodiversity crisis, with important impacts on ecosystems [1,2,3], and huge economic losses [4,5]
Because of potential problems with multi-collinearity [54] we further reduced our variables to four: Mean Temperature of the Wettest Quarter (MTWQ); Mean Temperature of the Coldest Quarter (MTCQ); Precipitation of the Wettest Quarter (PWQ); Precipitation of the Coldest Quarter (PCQ)
The geographical projections of the grey squirrel’s climatic niche predicted by the three models showed that NRM failed to predict a large extent of the invasive range in the Eastern parts of the United Kingdom, whereas it accurately predicted an unsuitable area in Western Scotland, where the species is absent

Summary

Introduction

Species introduction represent one of the main factors in the ongoing biodiversity crisis, with important impacts on ecosystems [1,2,3], and huge economic losses [4,5]. Given that eradication and control of established populations of introduced species is costly and difficult to implement [6,7,8,9], strategies aiming at mitigating these impacts should focus on prevention and early warning and rapid response. The implementation of such strategies requires the development and adoption of screening tools designed to identify potentially harmful species before importing them into a country [10], or to facilitate prompt response in the event of new introductions [11]. When recording a new invasion, it is important to have quick screening tools to support decision making in terms of appropriate responses [11]

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