Boom and bust cycles of black-tailed prairie dog populations in the Thunder Basin grassland ecosystem

Abstract

Black-tailed prairie dogs (Cynomys ludovicianus) exhibit boom and bust cycles in landscapes where they are affected by outbreaks of plague caused by the introduced bacterium Yersinia pestis. We examined spatiotemporal dynamics of black-tailed prairie dog colonies in the Thunder Basin National Grassland, Wyoming over a period of 21 years. The colony complex experienced three plague epizootics during that time, and consequently three boom and bust cycles. The entire prairie dog colony complex collapsed over a 1-year period during the first and third epizootics, and over a 3-year period during the second epizootic. The boom and bust cycles were characterized by relatively rapid contractions in total area occupied by prairie dogs during a plague outbreak (e.g., >99% decline from 10,604 ha to 47 ha over 1 year [2017–2018]) followed by much slower recovery times (e.g., an increase from 410 ha to 10,604 ha over 11 years [2006–2017]). Prairie dogs occupied a total of 10,604 ha during at least one survey within the study period, but much of the area was not continuously occupied over time. We found that each of the three plague outbreaks occurred in years with highly connected prairie dog colonies and slightly above-average temperatures and summer precipitation, which were preceded by a dry year. Although plague outbreaks were associated with climatic conditions, we were unable to detect a role of climate in driving colony expansion. Our results illustrate the cyclic and extreme nature of fluctuations in black-tailed prairie dog colony size and distribution in a landscape where plague occurs and illuminate some of the drivers of these cycles. Further, our work shows how introduced diseases can dramatically influence populations of a keystone species, with important consequences for the broader ecological system.

Disease and weather induce rapid shifts in a rangeland ecosystem mediated by a keystone species (Cynomys ludovicianus)

“…Our conceptual model focused on disease as a driver of wildlife community structure independent of climate, but climatic variability can also influence the probability of plague epizootics (Eads & Biggins, 2017). There have been three major plague outbreaks in Thunder Basin in the past 20 years, with each occurring in a relatively average precipitation year following a dry one (Davidson et al, 2022). While this pattern does not hold true in every landscape (Savage et al, 2011; Stapp et al, 2004), other studies have also linked plague epizootics with transitions from dry to wet years (Eads & Biggins, 2017).…”

“…Prairie dog colonies were dominated by western wheatgrass, plains prickly pear (Opuntia polyacantha), and short-lived forb species (e.g., wooly plantain [Plantago patagonica], desert madwort [Alyssum desertorum], common pepperweed [Lepidium densiflorum]). Typical of most extant prairie dog complexes, the Thunder Basin Ecoregion has experienced multiple cycles of colony growth followed by outbreaks of sylvatic plague (2000 and2007;Cully Jr. et al, 2010), with the most extreme event in the last 20 years occurring at the end of the growing season in 2017 (Davidson et al, 2022).…”

“…Following a plague event in the summer and fall 2017, mapping efforts were complicated by extreme contraction in active colonies. In response, we used a two-phase approach to mapping in 2018 (Davidson et al, 2022), with the first phase consisting of surveys conducted in April-July of point grids spaced at 600 m intervals to detect signs of prairie dog occupancy. In autumn, phase two consisted of revisiting areas with activity and mapping active burrows.…”

“…Mapping in 2019 consisted of revisiting previously identified occupied areas and mapping in those areas. Please refer to Davidson et al (2022) for additional methodological details. We did not directly quantify prairie dog density in the study area over time, but did observe burrow densities of 150/ha and confirmed active (via scat or active digging) burrow densities of 68/ha in 2017 (Duchardt et al, 2021).…”

“…Drastic fluctuations in local prairie dog abundances across time due to plague ("boom-and-bust" cycles [Davidson et al, 2022]) are likely to impact wildlife communities by reducing the availability of both prey and habitat. However, in considering the impacts of plague at the community level, it is important to recall that many rangeland wildlife species possess innate coping strategies for habitat variability.…”