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Ana Desiree Davidson
Research
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 (Cynomys gunnisoni and C. ludovicianus) and banner-tail kangaroo rats (Dipodomys spectabilis) on plant and arthropod communities. We 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. Our 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.
We established a long-term, large-scale experiment in the Janos grasslands, Chihuahua, Mexico that simultaneously manipulates both cattle and prairie dogs (C. ludovicianus). The goal of our 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. I am leading this research project under the advisorship of Dr. Gerardo Ceballos and Dr. Jim Brown, 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).Our 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).
Janos Biosphere Reserve
The Janos Biosphere Reserve was established in 2009. It covers one million hectares in northern Mexico, and borders the United States. The researve 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 and agricultural development are seriously threatening the biodiversity of this region (Ceballos et al. 2010). The Janos Prairie Dog and Cattle Study (JPACS) is a part of a much broader conservation and research effort to restore and properly 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.
Restoration Ecology and Burrowing Mammals
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. 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.
During the summer of 2005, my colleagues and I relocated several hundred prairie dogs from the Santa Fe Railyard to the SNWR 1) to help restore the SNWR grassland to its native state and 2) to study the ecological effects of the prairie dogs on the grassland landscape as they recolonize the grassland. This work has been a part of a large collaboration among biologists with Prairie Ecosystems Conservation Association, the United States Fish and Wildlife Service, and the Sevilleta Long-Term Ecological Research Program, Department of Biology at UNM. Duing the summer of 2010, we collaborated again with the USFWS to reintroduce another 600 prairie dogs to the Sevilleta in additional study plots.
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.
My colleagues and I are currently 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 vertebrate extinction risk to help inform conservation. In our recent PNAS papers, we 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). We have a number of related papers in preparation.
We are working 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 (Brown et al., In Review).
Information contained in this document is © copyright Ana D. Davidson, 2010. All rights reserved.
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