3.2 Niche overlap and niche dynamics
New England cottontail and eastern cottontail environmental niches had high overlap (D =0.79, I = 0.89). We found support for hypothesis 1, that niches would have more overlap than random, withD both more similar (p -value <0.01) and equivalent (p -value 0.01) than random and I more similar than random (p -value 0.01;Table 1).
Overall, support for hypotheses 2-4 differed based on the test used for niche conservatism (similarity versus equivalency; Table 1). For hypothesis 2, we found the expansion value, or the proportion of the eastern cottontail niche without New England cottontail is higher than random, was supported under the equivalency test (p -value 0.00) but did not find support for this hypothesis under the similarity test (p -value 0.97). For hypothesis 3, we found the stability value, or the proportion of the New England cottontail niche also containing the eastern cottontail niche was higher than random, was supported for the similarity test (p -value 0.03), but not the equivalency test (p -value 1.00). For hypothesis 4, we found the unfilling value, or the proportion of the New England cottontail niche without eastern cottontail was lower than random, was supported under the similarity test (p -value <0.01), but not the equivalency test (p -value 0.87; Table 1).
Overall, we found niche dynamics for New England cottontail and eastern cottontail changed minimally with current environmental conditions (Figure 4a). The PCA explained 30.10% of the variation observed in the predictors with dimension 1 accounting for 17.67% and dimension 2 accounting for 12.43% of the variation (Figure 4b). The first dimension largely represented a gradient of increasing proximity to young forest and understory vegetation represented by negative correlation values with distance to regenerating forest, transitional to forest, and barberry, mixed invasive and greenbrier understories (r = -0.66, -0.55, -0.61, -0.59, -0.51). Dimension 2 largely represents a gradient of decreasing annual precipitation, elevation, and distance to building represented by negative correlation values (r = -0.64, -0.62, -0.60). We found varying annual precipitation, elevation, and distance to shrublands did show niche shifts, where annual precipitation below 1375 mm, elevation above 125 m, and adjacent to shrublands favored New England cottontail (Figure 5).