Vickie Bakker

Education

Research interests

Data

Publications

Education

Ph.D. Ecology, 2003. University of California, Davis.

Post-baccalaureate coursework, 1990 -1994. University of Alaska and University of Washington.

B.A. English and environmental studies, 1989. Dartmouth College.

Research interests

· Movement and territorial behavior of animals in fragmented landscapes

· Demography and habitat relations of rare and endangered species

· Evolution of body size

Movement and territorial behavior of animals in fragmented landscapes

I am interested in understanding how animals perceive habitat and in testing key assumptions of conservation biology theory linked to behavior. I pursued these questions in several ways through my dissertation research on red squirrels (Tamiasciurus hudsonicus) in fragmented forests of southeastern Alaska. Conservation biology theory calls for reserve systems that allow inter-reserve movement, typically via corridors, yet we know little about the factors influencing movement behavior. I examined movement behavior at multiple spatial scales, forcing red squirrels to make decisions by releasing them off their home ranges in an array of settings, recording ensuing movements with direct observation, tracking spools, and radiotelemetry.

On a fine scale, I performed a correlative study of path selection to determine microhabitat features squirrels favored when on unfamiliar ground, then corroborated my results experimentally by releasing squirrels in manipulated test plots (Bakker in revision). Manipulations altered movements, suggesting microhabitat restoration could enhance travel in certain areas.

Working at a larger spatial scale, I identified determinants of gap-crossing (Bakker and Van Vuren 2004) by red squirrels and found that squirrels were more likely to cross clearcut gaps if the detour efficiency (distance across clearcut/distance via forested detour) was low. Detour efficiency has recently been shown to influence the movements of forest passerines, but my research is the first demonstration of its importance to a mammal, hinting at a potentially more general pattern among forest vertebrates. These animals appear able to compare both the relative risk or cost of travel in different habitats and the length of alternate routes. Consequently, they may cross risky habitats in favor of safer routes such as corridors if long detours are required.

To further investigate how red squirrels perceive habitat, I examined seeds remaining on cones foraged upon by red squirrels in clearcuts. I found that giving-up densities (GUDS) increased with distance from the forest edge, indicating that squirrels perceived predation risk as higher in the center of clearcuts. I also studied whether habitat differences explained variation in territorial behavior. Sitka spruce (Picea sitchensis), an uncommon food resource, predicted territorial behaviors such as calling rate, midden presence and excursions, while mean tree size, which may serve as an indicator of overall food resources, predicted home range size.

Demography and habitat relationships of rare and endangered species

A second research interest is identifying scientifically based measures for protecting rare species, acting in partnership with government agencies or non-profit organizations responsible for species and land management. I am currently working with The Nature Conservancy (TNC) to perform demographic analyses and design monitoring protocols for the Santa Cruz Island fox (Urocyon littoralis santacruzae), which has declined precipitously in the last decade and is currently one of the most endangered carnivores in North America. My work on behalf of this species is intended to help TNC monitor the effectiveness of its intensive efforts to protect the species.

Similarly, I researched, along with colleague Kim Hastings, the habitats and den trees used by northern flying squirrels (Glaucomys sabrinus) in the Tongass National Forest (TNF) in southeastern Alaska for the US Forest Service. Flying squirrels are one of the forest's vertebrates thought to be most vulnerable to logging. We found that TNF flying squirrels were more dependent on weatherproof dens than those in more southerly forests, often denning low in trees or underground where cavities are more insulated but also more vulnerable to predators (Bakker and Hastings 2002). We formulated simple recommendations for tree retention that took advantage of spatial autocorrelation in features predicting den presence.

Evolution of body size

A third research focus is macroecological investigations of patterns in body sizes at different spatial scales and in different regions to gain insights into the processes driving the evolution of communities and species. I investigated, along with colleague Doug Kelt, the body size distributions of South American mammals from the continental scale to the local scale (Bakker and Kelt 2000). We found that, unlike the patterns reported for North America, body size distributions of mammals did not become uniform at local scales in tropical rainforest areas of South America, although they did in temperate regions of the continent. We concluded that this scaling pattern likely arose because rainforest mammals partitioned resources both horizontally and vertically due to the productivity of the tropical rainforest canopy, underscoring habitat complexity as a factor contributing to the latitudinal gradient in species richness.

I am currently performing two tests of the island rule, which states that large mammals tend toward dwarfism and small mammals toward gigantism when isolated on islands, apparently due to a reduction in resources, predation, and competition. I am evaluating changes in body size and wool traits in feral sheep released from domestication on Santa Cruz Island in 1850. Body mass data from island lambs reared in captivity allow separation of genetic and environmental influences. Similarly, I am comparing the body mass and warning coloration patterns of the Channel Island spotted skunk (Spilogale gracilis amphiala) to those of mainland skunks using capture records and museum specimens.

Data

Gap-crossing decisions and potential predictors, supplemental data for Bakker and Van Vuren 2004.

Publications

Bakker, V. J and D. H. Van Vuren. 2004. Gap-crossing decisions by the red squirrel (Tamiasciurus hudsonicus), a forest-dependent small mammal. Conservation Biology 18: 689-697.

Bakker, V. J. The influence of micro-habitat features on the movements of red squirrels (Tamiasciurus hudsonicus) on unfamiliar ground. In revision.

Bakker, V. J., D. K. Garcelon, E. T. Aschehoug, K. R. Crooks, C. Newman, G. Schmidt, D. H. Van Vuren, and R. Woodroffe. Current status of the Santa Cruz Island Fox (Urocyon littoralis santacruzae). In press. Proceedings of the Sixth California Islands Symposium.

Bakker, V. J. and K. Hastings. 2002. Den trees used by northern flying squirrels (Glaucomys sabrinus) in southeastern Alaska. Canadian Journal of Zoology 80: 1623-633.

Bakker, V. J. and D. A. Kelt. 2000. Scale-dependent patterns in body size distributions of Neotropical mammals. Ecology 81: 3530-3547.

Last revised: May 16, 2004