Ecological Niche Shifts Are Rare in Invasive Mammals

ABSTRACT

Huntley and Wilkinson ( Journal of Biogeography , 53, 2025) analysed climatic niche conservation in the invasive eastern grey squirrel ( Sciurus carolinensis ) and concluded that a niche shift occurred between North America and Europe. Nevertheless, their study suffers from two major flaws: ignoring prior literature and misinterpreting ecological niche theory. Previous research (Qiao et al. Scientific Reports , 7, 2017) demonstrated that reported niche shifts in this species were methodological artefacts, emphasizing the need for rigorous quantitative approaches and consideration of accessible environments. Huntley and Wilkinson relied on qualitative visual assessments, neglecting established methods for niche comparison. Furthermore, their framework confuses realized and fundamental niches, the latter being key to detecting evolutionary changes. Differences in realized niches may still be informative but often reflect environmental availability or biotic interactions, not physiological adaptation. True niche shifts in mammals require rapid evolutionary changes, which are unlikely during invasions. Thus, claims of niche shifts in S. carolinensis remain unsupported and should be interpreted cautiously for this and other mammal invaders.