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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 (see Publications). 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. 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.
Grassland Ecology and Mammalian Herbivores
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 primary mechanisms that drive grassland ecosystem dynamics and biodiversity. Megaherbivores and small burrowing herbivores 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 systems.
The primary objective of my postdoctoral research is to determine the independent and interactive effects of domestic megaherbivores (cattle) and small herbivores (prairie dogs) on semi-arid grassland ecosystems in the Janos region of northern Chihuahua, Mexico. This research manipulates cattle and prairie dogs simultaneously using a long-term experiment to understand how these herbivores impact grassland community structure and ecosystem dynamics. 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).
The Janos region is in the process of being declared a biosphere reserve. The region supports the largest remaining colony of black-tailed prairie dogs (C. ludovicianus), and a high diversity of threatened and endangered wildlife. Yet, pressures from cattle grazing and agricultural development are seriously threatening the biodiversity of this region. 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
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 (bubonic) 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 fox.
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.
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 guiding conservation and policy.
I am now starting to apply such approaches to understanding global-scale patterns in mammalian biodiversity loss and the human impacts driving those trends. This work is in collaboration with Dr. Gerardo Ceballos.
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