Evaluating ecological relationships and niche breadth among historically sympatric <i>Canis</i> taxa using isotope analysis

Abstract Persecution of wild North American wolf-like canids (subfamily Caninae, genus Canis) by humans has severely reduced their geographic ranges and diversity. This is notably evident in the Southern Great Plains region spanning the states of Texas, Oklahoma, and New Mexico, United States. Historically, this region supported the now locally extinct Great Plains Wolf (C. lupus nubilus) and Red Wolf (C. rufus). Current wild wolf-like canid diversity largely consists of the Coyote (C. latrans), while the Mexican Wolf (C. lupus baileyi) is primarily restricted to the recovery program area. As interspecific antagonism and competition are known to affect behavior and resource use among wolf-like canids, historical sympatry raises important ecological questions. Stable isotope analysis (δ13C, δ15N) of bone collagen was employed to evaluate potential change in the isotopic niche of coyotes following wolf extirpation within the study region and to examine niche breadth and overlap among modern wolves and coyotes. Stable isotope data and radiocarbon dates were additionally obtained for a sample of wolves purported to be pre-Industrial, and niche breadth was compared to modern wolf samples. Kernel estimation density methods were used to estimate isotopic niche breadth and degree of overlap in group-wise comparisons. Results suggest a reduction in the isotopic niche breadth of coyotes following wolf extirpation, and substantial overlap in niche area between red wolves and coyotes, suggesting potential historical competition. Mexican wolves had a more constrained and divergent niche breadth, which may be shaped by habitat and prey preference as well as competition. Overlap was minimal among modern and pre-Industrial wolves, likely reflective of sample size and collection localities. These findings provide insights into how Coyote niche breadth may shift following reduced wolf presence and resource use patterns among sympatric wolf-like canids.