COS 59-2 - CANCELLED - Disease drives rapid shifts in a keystone-mediated grassland ecosystem

Background/Question/Methods

Habitat loss and changing climate have direct impacts on native species but can also interact with disease pathogens to influence wildlife communities. In the North American Great Plains, black-tailed prairie dogs (Cynomys ludovicianus) are considered a keystone species, serving as a prey resource for raptors and carnivores while simultaneously engineering habitat structure for numerous associated species. Severe reductions of grassland habitat paired with lethal control driven by agricultural conflict has severely reduced the abundance of this species. Novel disease dynamics caused by epizootic plague (Yersinia pestis) within prairie dog colonies have further destabilized associated wildlife communities, leading to collapse of many colony complexes that did not co-evolve with this novel pathogen. We capitalized on a natural experiment — collecting data on prairie dog distributions, vegetation structure, avian abundance, and mesocarnivore and ungulate occupancy before (2015–2017) and after (2018–2019) a major plague event in northeastern Wyoming, USA.

Results/Conclusions

Plague decimated black-tailed prairie dog populations in what was then the largest extant colony complex in the world, reducing colony area from over 16,000 ha to less than 100 ha. We documented dramatic declines in mesocarnivore occupancy and raptor abundance post-plague, with probability of occupancy or abundance approaching zero in species that rely on prairie dogs for a high proportion of their diet (e.g., ferruginous hawk [Buteo regalis], American badger [Taxidea taxus], and swift fox [Vulpes velox]). Following the plague outbreak, abnormally high precipitation in 2018 hastened vegetation recovery from prairie dog disturbance on colonies where constant herbivory had formerly maintained shortgrass structure necessary for certain colony-associates. As a result, we observed large shifts in avian communities on former prairie dog colonies, including near-disappearance of mountain plover (Charadrius montanus) and increases in mid-grass associated songbirds (e.g., lark bunting [Calamospiza melanocorys]). Our research demonstrates how disease-induced loss of a keystone species can induce drastic and rapid shifts in wildlife communities, highlighting the interactive role of precipitation in these shifts. Although grassland taxa co-evolved with high spatiotemporal variation, fragmentation of remaining North American rangelands paired with higher-than-historical variability in climate and disease dynamics are likely to destabilize these systems in the future.