Abstract
Niche conservatism is the tendency of related species to retain ancestral tolerances after geographic separation. We used Ecological Niche Modelling and Principal Components Analysis of bioclimatic and habitat variables to describe the extent of the species niche, and degrees of bioclimatic–habitat niche conservatism within the mountain hare (L. timidus) clade. Mountain hare niche space was contrasted with that of the European hare (L. europaeus), to shed light on species interactions in contact zones throughout Europe. All five subspecies of mountain hare had quantifiably distinct niches. Fennoscandian (L.t. sylvaticus, L.t. timidus) and highland (L.t. scoticus, L.t. varronis) subspecies, however, were most similar, exhibiting greatest apparent niche conservatism. They inhabit tundra, boreal forest and uplands, and, hence are presumed most similar to the ancestral form. The Irish hare was distinct, being consistently distinguished from other mountain hares in both 2D and nth dimensional (4D) niche space. The ecological distinctiveness of the Irish hare provides further evidence that it is an Evolutionarily Significant Unit, particularly vulnerable to displacement by introduced European hares with which it competes and hybridises. Projections under global climate change suggest that, by 2070, bioclimatic space for invasive European hares in Ireland will expand (by 79%) but contract for endemic Irish hares (by 75%), further facilitating their replacement. The near complete species replacement of the heath hare (L.t. sylvaticus) in southern Sweden, where the European hare has also been introduced, may suggest a similar fate may be in store for the Irish hare.
Highlights
The controversial concept, ‘niche conservatism’, is the tendency of emergent species to retain their ancestral ecological traits such that closely related species may be more ecologically similar than would be expected based on their phylogenetic divergence (Wiens et al 2010)
We aimed to describe the degree of niche conservatism within the mountain hare clade in Europe, capturing the niche of each subspecies
The range polygons for each mountain hare subspecies were extracted from the parent IUCN range polygon and sub-divided into geographically isolated populations i.e. Ireland, Scotland, and the Alps, whilst the Fennoscandian mountain hare subspecies ranges were delineated according to Bergengren (1969)
Summary
The controversial concept, ‘niche conservatism’, is the tendency of emergent species to retain their ancestral ecological traits such that closely related species may be more ecologically similar than would be expected based on their phylogenetic divergence (Wiens et al 2010). A niche comprises a multivariate set of abiotic and biotic conditions which facilitate the persistence of a species, and to which it is suitably adapted (Hutchinson 1957). The fundamental niche is unconstrained by limiting biotic factors such as ecological competition, predation, dispersal ability, and environmental conditions (Hutchinson 1957; Wiens and Graham 2005). The realised niche is described as the fundamental niche constrained by limiting factors, i.e. the space occupied by, and the resources available to, an organism (Hutchinson 1957; Soberon 2007). Population viability depends on a degree of environmental stability or adaptive predictability, and climate and habitat are key factors (Soberon and Peterson 2005; Jakalaniemi 2011). In the absence of gene flow, populations may diverge genetically while occupying similar habitat to ancestral species, and the species niche is conserved
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