DOGS, DEATH, AND DIETARY BREADTH: THE LINK BETWEEN SPECIES DURATION AND DIETARY SPECIALIZATION IN CANIDS

Understanding the factors contributing to extinction risk in species is vital for understanding macroevolutionary patterns and planning conservation strategies. One factor which has been frequently cited as driving the extinction of taxa is dietary specialization, whereby increasingly narrow dietary niche space is hypothesized to reduce resilience to environmental perturbations. This pattern, dubbed the macroevolutionary ratchet, has been exemplified in the exceptional fossil history of the Canidae. However, dietary specialization and its link to extinction has traditionally been inferred from morphological traits rather than from direct dietary reconstructions. Dietary plasticity, which is not captured by morphology, truly defines a species’ dietary niche. We tested the association between dietary specialization and extinction by quantifying the dietary niche of 10 extinct and 4 extant North American canids spanning 33.3 million years of evolution using Dental Microwear Texture Analysis (DMTA). DMTA quantifies microscopic wear patterns on tooth enamel to capture a comprehensive picture of dietary resource use. Species’ dietary specialization was calculated using multi-dimensional Bayesian standard ellipsoid volumes of DMTA parameter space. Species durations, estimated from occurrences via PyRate, were used to create a series of multiple linear regressions for correlation with the standard ellipsoid volumes and morphological traits from published studies used to previously estimate dietary specialization in canids. Model ranking for fossil canids shows higher support for correlation between DMTA derived dietary niche breadth and species durations than between morphological traits and species durations (ΔAICc >3). Counter to expectations, we observed a positive correlation between dietary specialization and lineage duration (p=0.02; R²_adj = 0.54), and that specialization was not correlated with traditionally used dietary categories (i.e. hypo-, meso-, or hypercarnivory). Our results therefore contradict the prevailing hypothesis, suggesting that specialization in diet alone was not enough to drive extinctions in canids. Instead, we suggest that dietary specialization offers selective advantages that facilitated the coexistence of a diverse canid community through time.