PBS interview on prairie dog ecology and conservation

Ecology and Conservation of Burrowing Mammals

The world’s grasslands are fundamentally shaped by an underappreciated key functional group of social, semi-fossorial, herbivorous mammals. Examples include the phylogentically similar species of prairie dogs of North America (NA) (Cynomys spp.), ground squirrels (Sciuridae spp.) of NA, Eurasia, and Africa, and marmots (Marmota spp.) of NA and Eurasia, but also more distantly related but functionally similar plains vizcachas (Lagostomus maximus), Patagonian maras (Dolichotis patagonum) and degus (Octodon degus) of South America, pikas (Ochotona spp.) of Asia, ice rats (Otomys sloggetti) and springhares (Pedetes capensis) of Africa, and burrowing bettongs (Bettongia lesueur) and southern hairy-nosed wombats (Lasiorhinus latifrons) of Australia. These burrowing mammals often live in colonies ranging from 10s to 1000s of individuals. They collectively transform grassland landscapes through their burrowing and herbivory, and by grouping together socially, they create distinctive habitat patches that serve as areas of concentrated prey for many predators.  

Yet, burrowing mammal populations have declined dramatically because of human impacts. Indeed, because grasslands provide the world’s most important habitat for agricultural and livestock production, burrowing mammals are often in direct conflict with human activities. Human-mediated introductions of exotic species, including disease-causing organisms, and overhunting are also reducing their populations. What we know about the few well-studied species suggests that burrowing mammals likely play widespread and important ecological roles, and that their loss can have cascading effects on grassland ecosystems on which both humans and wildlife depend. My research seeks to address these challenges facing prairie dogs and associated species in the central grasslands of North America.
(Davidson et al. 2012, Frontiers

Islands of Habitat

Diagram illustrating the distinctive islands of habitat that burrowing mammals create across multiple spatial scales with their mounds (top), individual colonies (middle), and colony complexes (bottom), resulting in increased habitat heterogeneity and biodiversity across the landscape. This illustration is based on black-tailed prairie dogs in the Great Plains grasslands of NA. Drawing is by Sharyn N. Davidson.  (Davidson et al. 2012, Frontiers)

  Ecological Role

Conceptual diagram showing the trophic (herbivory, prey) and ecosystem engineering (clipping, burrow construction, and mound building) effects of burrowing mammals on the grassland ecosystem, based on the roles of the best-studied species: the black-tailed prairie dog (C. ludovicianus) in NA. Plus signs indicate an increase, minus signs indicate a decrease. Black arrows depict the effects of burrowing mammals (e.g., prairie dogs), green arrows depict the impacts of megaherbivores (e.g., bison), and the red arrow indicates the role of predators. Drawings are by Sharyn N. Davidson.  (Davidson et al. 2012, Frontiers)

Prairie dogs (Cynomys spp.) play important roles in shaping the central grasslands of North America. By grazing and clipping vegetation they create a low mat of dense forbs and grazing tolerant grasses, and dot the landscape with numerous mounds. Their colonies represent unique islands of open grassland habitat that attract numerous animals, such as burrowing owls and mountain plovers (Charadrius montanus), and predators that rely on prairie dogs as a primary food source, such as coyotes, American badgers (Taxidea taxus), raptors, and the highly endangered black-footed ferret (Mustela nigripes). Although the magnitude of these impacts can vary by prairie dog species, colony density, or other site-specific factors, prairie dogs play important ecological roles in grasslands across their range.

Prairie dog populations have declined by about 98% over the last century, and are consequently identified as a Species of Greatest Conservation Need by the state of New Mexico. Much of their decline is due to poisoning, introduced sylvatic plague, habitat loss, shooting 6, and increasingly, climate change in the southern portion of their range. The dramatic decline in prairie dogs has resulted in consequent losses in associated species and grassland habitat. Indeed, because prairie dog populations have undergone severe numerical reductions, their key ecological roles have been greatly diminished throughout much of their geographic range. Loss of prairie dogs has resulted in declines in species associated with the habitats they create, including the burrowing owl and mountain plover, and those dependent or heavily reliant upon prairie dogs as prey, including black-footed ferrets and ferruginous hawks (Buteo regalis). Additionally, grasslands have been invaded by shrubs in areas where black-tailed prairie dogs (C. ludovicianus) have been poisoned in the southern distribution of their range, demonstrating their role in maintaining grasslands and the ecosystem services they provide to humans. Prairie dogs are needed in large numbers across the greater grassland landscape in order to support associated species and maintain the unique islands of important grassland habitat and associated biodiversity. Because of their ecological importance there is much interest in restoring and protecting their populations. In fact, the USFWS black-footed ferret recovery plan specifically states, “We believe the single, most feasible action that would benefit black-footed ferret recovery is to improve prairie dog conservation. If efforts were undertaken to more proactively manage existing prairie dog habitat for ferret recovery, all other threats to the species would be substantially less difficult to address” 

Cascading effects of keystone species declines

Conceptual diagram illustrating how the loss of a keystone species cascades throughout an ecosystem, using the black-tailed prairie dog (Cynomys ludovicianus) in North America’s central grasslands as an example. Declines in prairie dogs result in the loss of their trophic (herbivory, prey) and ecosystem engineering (clipping, burrow construction, and mound building) effects on the grassland, with consequent declines in predators [e.g., black-footed ferrets (Mustela nigripes), raptors, swift and kit foxes (Vulpes velox, V. macrotis), coyotes (Canis latrans), badgers (Taxidea taxus)], large activity [e.g., Bison (Bison bison)], invertebrate pollinators, and species that associate with the open habitats and burrows that they create [e.g., burrowing owls, (Athene cunicularia), mountain plovers (Charadrius montanus), pronghorn (Antilocapra americana), swift and kit foxes, cottontail rabbits (Sylvilagus spp.), rodents, and many species of herpetofauna and invertebrates]. Black arrows depict the effects of prairie dogs. Plus signs indicate an increase in an ecosystem property as a result of the loss of prairie dogs, minus signs indicate a decrease. Drawings are by Sharyn N. Davidson. (Figure taken from Bergstrom et al. 2013)​

Keystone Species Interactions

 A fundamental goal of ecology is to understand the underlying mechanisms that regulate community structure and biodiversity. In many ecosystems, certain species play a central role in the organization of communities. These species are often referred to as keystones, and are defined by having distinctive and disproportionately large impacts on community structure and ecosystem function relative to their abundance. Such species can affect ecosystems through a variety of processes, from top-down effects through the consumption of prey to bottom-up effects through ecosystem engineering. Although keystone species co-occur in many systems, their interactive effects have received little attention.

For my dissertation, under the advisorship of Jim Brown and in collaboration with Dr. David Lightfoot, I evaluated the separate and interactive effects of prairie dogs (C. gunnisoni and C. ludovicianus) and banner-tail kangaroo rats (Dipodomys spectabilis) on plants, arthropods, and lizards. I found that the impacts of prairie dogs and kangaroo rats were unique, and the habitats they created supported different assemblages of plants and  arthropods, and lizards. Where both rodent species co-occurred, there was greater heterogeneity and species diversity on the landscape. These results suggest that the interaction of multiple keystones, especially those with engineering roles, results in unique and more diverse communities in time and space (Davidson and Lightfoot 2006, Ecog.; 2007, Ecog.; 2008, JAE; and Davidson et al. 2008, JAE). 

Grassland Ecology and Mammalian Herbivores 

 Janos Prairie Dog and Cattle Study (JPACS)

Grasslands are among the most imperiled ecosystems in the world due to agricultural intensification, desertification, and the loss of native species. In order to manage and conserve these systems in the face of multiple, and often conflicting interests, there is a critical need to understand the mechanisms that drive grassland ecosystem dynamics and biodiversity. 

Megaherbivores and small burrowing mammals are known to play key roles in the structure and function of grasslands worldwide. Although domestic livestock have replaced native megaherbivores throughout much of the world, surprisingly little is known about their interactive effects with native wildlife and the consequent effects on grassland ecosystems.

A critical issue for conservation of grasslands around the world is the need to maintain the important functional role of keystone burrowing mammals, like prairie dogs, while simultaneously managing for livestock production. Competition with cattle has been used to justify extensive programs to eradicate prairie dogs and other herbivorous rodents from grasslands throughout the world. In the U.S., a century of prairie dog “pest control” programs have been largely responsible for reducing their populations to 2-5% of their historic numbers, and these control efforts still continue today. 

I established a long-term, large-scale experiment in the Janos grasslands, Chihuahua, Mexico that simultaneously manipulates both cattle and prairie dogs (C. ludovicianus), for my postdoctoral research under the advisement of Drs. Gerardo Ceballos and James H. Brown. The goal of this work is to help elucidate the relationships and interactive roles of these important herbivores, key to understanding the impact of human activities on global grassland decline and implementing proper management. This work is in collaboration with a team of researchers from the National University of Mexico (UNAM), the University of New Mexico (UNM), and the United States Department of Agriculture - Agricultural Research Service (USDA-ARS). The research to date is showing that prairie dogs and cattle can have mutually beneficial relationships, and their combined effect on the grassland ecosystem can be synergistic (Davidson et al. 2010, Ecology).

JPACS study site on El Uno Ranch, owned by The Nature Conservancy and located within the Janos Biosphere Reserve

Here is a slideshow highlighting the initial results from the JPACS study

Janos Biosphere Reserve

Map of the Janos Biosphere Reserve
Our research group at UNAM led the establishment of the Janos Biosphere Reserve, which was decreed in 2009.  It covers one million hectares in northern Mexico, and borders the United States.  The reserve supports one of the largest remaining colony complexes of black-tailed prairie dogs, and a high diversity of threatened and endangered wildlife, including bison and black-footed ferrets.  

Yet, pressures from cattle grazing, agricultural development, and climate change are seriously threatening the biodiversity of this region (Ceballos et al. 2010, PLoS ONE). The Janos Prairie Dog and Cattle Study is a part of our much broader conservation and research effort to restore and sustainably manage this grassland system. Our approach is to recognize human well-being and the local agricultural community as an integral part of the ecological system and conservation strategy.  Our projects include studying: 1) population genetics and disease ecology of Janos prairie dogs; 2) prairie dog population dynamics under a rapidly changing climate; 3) the ecological relationships of prairie dogs and cattle and how their interactions impact the grassland ecosystem; 4) the role of prairie dogs and cattle in mesquite establishment and control; 5) ecosystem services prairie dogs provide; 6) sustainable cattle management; 7) porcupine population ecology. We also have a number of innovative and large-scale grassland restoration projects, including working with local agriculturalists to re-seed the land with native grasses, and reintroducing black-footed ferrets, bison, and prairie dogs

Restoration Ecology and Burrowing Mammals

Historic (red polygons) and current (yellow polygons) distribution of Gunnison’s prairie dogs at the SNWR
Ecological restoration involves initiating the recovery of an ecosystem through human intervention. In grassland ecosystems, ecological restoration often includes restoration of natural fire regimes, reintroduction of native species, reseeding of native perennial grasses, and/or removal or reduction of domestic livestock grazing.

The central grasslands of North America that stretch from southern Canada to northern Mexico have experienced large declines in its once most abundant native herbivore: the prairie dog. Prairie dogs are considered keystone species and ecosystem engineers of this grassland system, creating important habitat for many plants and animals through their burrowing and herbivory. They also provide an important prey resource for many predators. However, as a result of century long poisoning campaigns, sports shooting, introduced sylvatic plague, and habitat loss from desertification, agricultural development, and urbanization, their populations have declined by about 98% across their range.

The loss of the ecological role of prairie dogs from much of their range has resulted in a cascade of effects throughout the grassland system, reducing grassland biodiversity (Bergstrom et al. 2013, Conservation Letters). Indeed, many species associated with prairie dogs have declined to threatened or endangered species status, including black-footed ferrets, burrowing owls, ferruginous hawks, mountain plovers, and swift foxes.

Consistent with range-wide trends, Gunnison’s prairie dogs (C. gunnisoni) have been almost entirely eliminated from the Sevilleta National Wildlife Refuge (SNWR) Socorro County, NM, as a result of extensive poisoning campaigns in the 1960’s (before the refuge was established). Since these efforts, the SNWR has been missing this important herbivore from its grasslands.

Since 2005, we have relocated thousands of prairie dogs from urban areas to the SNWR. Prairie dogs now occupy four colonies across about 50 ha of the SNWR (Davidson et al. 2014, JWM). The goal of this work is to: 1) help restore the SNWR grassland and its native keystone rodent, 2) study the population dynamics of the reintroduced prairie dogs over time to inform management and conservation efforts in the semi-arid parts of their range under climate change, and 3) quantify the ecological effects of the prairie dogs on the grassland landscape as they recolonize it. This project is a large collaborative effort among the SNWR, the Sevilleta Long-Term Ecological Research Program, Department of Biology at UNM, Prairie Dog Pals of Albuquerque, and the New Mexico Department of Game and Fish. Our recent efforts involve conducting comparative studies with recently reintroduced populations in a wetter grassland environment at the Vermejo Park Ranch in northern New Mexico.

The reestablished colonies play an important role in education and outreach. Currently, a graduate student, Chuck Hayes, is conducting his doctoral research on the physiology and demography of the reintroduced animals, and an undergraduate, Kevin McKormic, recently completed his senior honor's thesis on their behavioral ecology. Additionally, every summer undergraduates through the National Science Foundation's Research Experiences for Undergraduates Program and student interns with the Sevilleta LTER and SNWR assist in the ongoing restoration and research.  

Here's a video of the prairie dog relocation efforts on the SNWR, created by undergraduate students working on the project.

Location of the Gunnison's prairie dog reintroduction study site at the SNWR
I recently started new research on our reintroduced colonies at the Sevilleta NWR to: 1) test the value of using non-invasive sampling techniques (camera traps) for studying prairie dog population dynamics and 2) determine if our reintroduction efforts have helped restore the functional roles of prairie dogs in the Sevilleta grasslands. ​This work is being funded by New Mexico Department of Game and Fish's Share with Wildlife Program. Our preliminary results from the Sevilleta NWR are exciting and encouraging, with over 1600 photos of animals from just our spring camera trapping alone. Our camera traps are capturing large numbers of photos of species associated with prairie dog colonies, including burrowing owls, black-tailed jackrabbits, desert cottontails, and coyotes, and many more photos of these animals on the prairie dog colonies compared to off-colony grassland areas. This is just the beginning of our project; we are still cataloging many photos. We also are obtaining neat photos that capture behavior of vertebrate species on prairie dog colonies, such as the photo of a burrowing owl pouncing on a badger as it crosses a prairie dog colony, in attempt to chase the badger off the colony. Burrowing owls will engage in this behavior while prairie dogs are also sounding alarm calls of a predator entering a colony (image E, below). This is a neat example of multiple species working together to fend off a shared predator. Overall, our very preliminary results suggest that the reintroductions of prairie dogs at the Sevilleta NWR may be helping to restore their functional role to the grassland ecosystem, and that the camera traps are able to capture large numbers of prairie dog photos. With this encouraging initial data, we are hopeful that the camera traps and associated occupancy analysis of this data may be able a viable non-invasive technique for sampling prairie dog populations and understanding their population dynamics for conservation and management purposes. 
Photos from our camera traps at the Sevilleta NWR showing: A, B, C) prairie dogs, D) a coyote, E) a burrowing owl pouncing the back of a badger crossing a colony, F ) a burrowing owl on a mound and a spotted ground squirrel standing up next to the mound, G) a coachwhip snake looking over grass, H) a pronghorn, I) a black-tailed jackrabbit, J) pronghorn running, K) an oryx, and L) mule deer running. 

Global Conservation, Biogeography, and Macroecology

Human impacts on Earth’s biodiversity are occurring at unprecedented rates. Biogeography and macroecology provide ecologists with the ability to evaluate large-scale patterns and statistical distributions of biodiversity and the causal factors driving those patterns. These approaches provide broad, global-scale information for informing basic ecological theory and guiding conservation and policy.

I am applying such approaches to understanding global-scale patterns in biodiversity loss and the human impacts driving those trends.  A major focus of this research centers around developing traits-based and spatially-explicit predictive models of mammalian extinction risk to help inform conservation (Murray et al, 2013, GCB).  In my recent papers, I used machine learning approaches to develop a map of the ecological pathways to extinction across mammals (Davidson et al. 2009, PNAS), and to identifty the drivers and global hotspots of extinction risk in marine mammals (Davidson et al. 2012, PNAS).  I have a number of related papers in preparation.

I am working with colleagues to address other basic ecological questions as well, such as how energy is allocated to production across different mammalian lineages (Hamilton et al. 2010, Proc R Soc B). Here, we found that despite striking differences in life histories among placental, marsupial, and monotreme mammals, the scaling of production rates is statistically indistinguishable across mammalian lineages. This suggests that all mammals are subject to the same fundamental metabolic constraints on productivity.

My colleagues and I also are taking a human macroecologcial perspective to understanding the energetic basis of human economies and its implications for economic and ecological sustainability (Brown et al. 2011, BioScience), and to providing macroecological insights for sustainability science (Burger et al. 2012, PLoS BiologyNekola et al. 2013, TREE; Brown et al. 2013, Ecological Engineering).