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).