Dietary Ecology of Coastal Coyotes (Canis latrans): Marine-Terrestrial Linkages from the Holocene to Present
- Author(s): Reid, Rachel Elizabeth Brown;
- Advisor(s): Koch, Paul L;
- et al.
Coyotes (Canis latrans) have an expanding North and Central American range and have also been shown to benefit from marine subsidies. Identifying the past and present role coyotes play in linking land and sea, and whether those links are lost or gained through time, will have important implications for the future management of this expanding species. The goals of my dissertation were to: (1) characterize the extent, magnitude and importance of a marine subsidy to modern coyotes on the central California coast; (2) determine whether Holocene coyotes on the central California Coast had an equivalent dietary niche; and (3) begin to evaluate (via predation and competition) the impact of this modern marine subsidy (where it occurs) on key terrestrial species.
To address these goals, I seasonally collected scats along coast-to-inland transects at three modern coastal sites around Monterey Bay over a span of two years. I used discriminant function analysis on a set of scat samples DNA-verified to species to show that morphological traits of gray fox, bobcat and coyote scats are not diagnostic of species; predictive models based on morphology have misclassification rates of ~35%. These results suggest that DNA-verification of scats is required in studies using scat to make claims about diet, abundance or habitat use by any of these animals in localities where they are sympatric. I characterized modern coyote diets using traditional scat analysis techniques in tandem with stable isotope analyses of scats themselves. I established a diet-to-feces discrimination factor for coyotes by analyzing multiple tissues from road kill carcasses and validated scat stable isotope dietary predictions by carefully comparing scat stable isotope values with isotopes measured in prey remains sourced from the scats.
For the investigation of Holocene coyote dietary ecology I selected six archaeological sites around Monterey Bay with a range of occupation periods spanning from ~3000 - 700 BP. This allowed for establishment of a Holocene baseline with which to compare modern coyote ecology over millennial timescales. My data point to both the existence of a marine subsidy to modern coyotes, and to a positive impact on coyote abundance. Sub-fossil isotope data suggest that Holocene coyotes did not consume marine-derived foods, despite the nearby presence of a mainland seal rookery. These data suggest that the use of marine resources by contemporary coyotes is a new behavior relative to their recent ancestors, perhaps enabled by reduced competition with either humans or other, now-absent consumers (e.g., grizzly bears, Ursus arctos californicus).