I am broadly interested in understanding pathogen spillover, establishment, and persistence in wildlife, with the goal of operationalizing theoretical results for application during emergent disease events. At the moment, this work primarily focuses on pneumonia dynamics of bighorn sheep. While we have excellent information on bighorn sheep pneumonia from a small group of intensively studied populations, understanding whether these findings can be generalized to other bighorn sheep herds living in a wide variety of contexts remains an on-going challenge.
BIGHORN SHEEP PNEUMONIA
It is increasingly accepted that bighorn sheep pneumonia results from introduction of Mycoplasma ovipneumoniae, usually originating from asymptomatic infections in domestic sheep. However, two key questions remain:
- Why do some bighorn populations become infected while others do not?
- Why do some bighorn populations experience on-going disease for decades, while others exhibit only minimal disease for relatively short periods of time?
Answering both of these questions is crucial for developing management strategies that benefit bighorn sheep population recovery throughout the west.
A ewe group at the Asotin Creek population in midsummer.
Our group focuses primarily on describing risk factors associated with pathogen introduction (a movement-centered project), and modeling variation in post-die-off population dynamics (a demography-centered project). A synopsis of some of our research is located at bighornhealth.org.
MOVEMENT AND PATHOGEN INTRODUCTION RISK
Bighorn sheep movements occasionally bring them into contact with domestic sheep, sparking species-to-species pathogen spillover events. Understanding the drivers of bighorn sheep movement is key for forecasting risk. We are working to understand movement dynamics of bighorn sheep in an effort to accurately forecast — and ideally, mitigate — pathogen introduction risk.
Among the hypothesized drivers of bighorn movement are:
- Demographic features of the individual: sex, age, subspecies, reproductive status
- Environmental context: habitat structure, climate, season
- Current demographic features of the herd: population size, sex structure
- Herd history: recent changes in population size, translocation history, etc.
Our work focuses on all four of these categories.
DEMOGRAPHIC RESPONSES AFTER DIE-OFF EVENTS
Bighorn population dynamics vary substantially in the aftermath of die-off events, but the causes of this variation are not well-understood. In this project, we are trying to understand what factors produce the observed variation, with the eventual goal of designing management that could improve post-die-off population responses.
Hypothesized factors associated with variation are:
- Features of the pathogen: M. ovipneumoniae strain involved, and its time since introduction into bighorns
- Features of the individual host: individual’s age, sex, and reproductive status; exposure history; and coinfections, genetic diversity
- Features of the host population: genetic diversity, behavior and movement dynamics, sex structure, reproductive synchrony
We are working to understand the role each of these factors plays in shaping long-term population dynamics after die-off events.
Both the movement and the demography projects couple mechanistic data from long-term intensive monitoring at a few focal populations with landscape-wide data on individuals from many populations, in highly variable ecological contexts. We collaborate with experts intensively studying bighorn sheep at the National Bison Range near Missoula, Montana; the Hells Canyon region of Idaho, Washington, and Oregon; Zion National Park; and the Muddy, Eldorado, McCullough, and River Mountains near Las Vegas, NV. I try to spend a minimum of eight weeks in the field every year, and most of my students put in well more than that!