4.2 Niche overlap analysis
New England and eastern cottontail had unusually high niche overlap and low niche differentiation for two species. Niche overlap analyses with other species have found a mix of both high and low niche overlap (Liu et al. 2017, Pascual-Rico et al. 2020, Quiroga and Souto 2022), but few studies with two mammalian species have found similarly high niche overlap values and low proportions of the native species niche not overlapping with the introduced species niche. Although New England and eastern cottontail niches were highly similar, they were not equivalent. The lack of equivalency suggests outside conditions or pressures may influence the prevalence of eastern cottontail across the state despite high niche overlap with New England cottontail.
One possible mechanism for the high observed overlap in environmental space, but not geographic space, is competition. Previous studies have identified competition between the two species and supported eastern cottontail as the dominant competitor (Probert and Litvaitis 1996, Cheeseman et al. 2018, Bischoff et al. 2023b ). Competition between New England and eastern cottontail was first observed in behavioral studies but lacked evidence of interference competition (Probert and Litvaitis 1996). A resource selection study of radio-tracked individuals associated interspecific competition with displacement of New England cottontail from young forest and shrubland habitat (Cheeseman et al. 2018). Relative abundance studies further supported interspecific competition, where patches with high numbers of eastern cottontail had lower New England cottontail abundance (Bischoff et al. 2023b ). A rigorous experimental test of New England cottontail-eastern cottontail competition, during all seasons and parts of the annual life cycle, would confirm the mechanism(s) and provide insight into paths for New England cottontail conservation in the continued face of eastern cottontail range expansion.