Genetic analyses are more sensitive than morphological inspection at detecting the presence of threatened Mojave desert tortoise (Gopherus agassizii) remains in canid scat and raven pellets

Subsidization of predator populations increases predation pressure on prey species, which is exacerbated when natural resources are scarce. Estimating the frequency of predation by subsidized predators on vulnerable species, especially low-density, long-lived species such as the federally threatened Mojave desert tortoise (Gopherus agassizii), allows landscape managers to evaluate the need for actions like reducing subsidies, discouraging predation by taste aversion, or predator removal. Most studies of Mojave desert tortoise predation have relied on morphological analysis to identify hard parts in predator scat. Here, we developed and validated a qPCR assay to test for the presence of Mojave desert tortoise in DNA extracted from scat and pellets. We used the assay to detect tortoise DNA in scat and pellets collected in a conservation easement adjacent to Boulder City, Nevada, from three Mojave desert tortoise predators: coyotes (Canis latrans), desert kit foxes (Vulpes macrotis arsipus), and common ravens (Corvus corax)-all of which consume anthropogenic resources. We compared the results of our qPCR assay to results from morphological analysis of the same samples and found that the qPCR method is much more sensitive at detecting the presence of tortoise remains. Although neither method can determine whether consumption was the result of predation or scavenging, nor how many individual tortoises were consumed, our findings indicate that conservation managers may benefit from focusing efforts on reducing subsidies that attract and support predators and on reducing tortoise mortality from predation.

Automated summary

Subsidization of predator populations increases predation pressure on prey species. The development and validation of a qPCR assay for detecting Mojave desert tortoise DNA in predator scat have shown that this method is more sensitive than morphological analysis. Conservation managers can benefit from reducing subsidies and predation to improve the protection of the tortoise.