Linking alternative food sources to winter habitat selection of herbivores in overbrowsed landscapes

During winter, ungulates in boreal forests must cope with high energetic costs related to locomotion in deep snow and reduced forage abundance and quality. At high density, ungulates face additional constraints, because heavy browsing reduces availability of woody browse, the main source of forage during winter. Under these severe conditions, large herbivores might forage on alternative food sources likely independent of browsing pressure, such as litterfall or windblown trees. We investigated the influence of alternative food sources on winter habitat selection, by studying female white-tailed deer (Odocoileus virginianus) living in 2 landscapes with contrasted browse abundance, recently logged and regenerated landscapes, in a population at high density and on a large island free of predators. We fitted 21 female white-tailed deer with Global Positioning System (GPS) collars and delineated winter home ranges and core areas. We measured snow conditions in different habitat categories and sampled vegetation in the core areas and in the rest of the home ranges to determine how forage abundance, protective cover, and snow conditions influenced habitat selection within the home range. In both landscapes, deer were less likely to use open habitat categories as snow accumulated on the ground. At a finer scale, deer inhabiting the regenerated landscape intensively used areas where balsam fir cover was intermediate with greater balsam fir browse density than in the rest of the home range. In the recently logged landscape, deer were more likely to be found near edges between clear-cuts and balsam fir stands and in areas where windblown balsam fir trees were present; the latter being the most influential variable. Although balsam fir browse was sparse and mainly out of reach in this landscape, deer increased the use of areas where it was present. Our results offer novel insights into the resource selection processes of northern ungulates, as we showed that access to winter forage, such as woody browse and alternative food sources, depends on climatic conditions and stochastic events, such as abundant compacted snow or windthrows. To compensate for these scarce and unpredictable food supplies, deer selected habitat categories, but mostly areas within those habitat categories, where the likelihood of finding browse, litterfall, and windblown trees was greatest. © 2011 The Wildlife Society.     

An inexpensive camera system for monitoring cavity nests

ABSTRACT A variety of pole‐mounted cameras have been developed for monitoring nest cavities. However, currently available camera systems may either be prohibitively expensive or difficult to assemble. I developed an inexpensive (<$500 US) and easily assembled camera system that allows researchers to monitor cavity nests from the ground. The system consists of a small camera, a cable connecting the camera to a ground‐level power source and laptop computer, and a flexible neck connecting the camera to a telescoping pole. During a study of Red‐headed Woodpeckers (Melanerpes erythrocephalus), I used this camera to inspect 16 nests and found that the images were clear and allowed accurate counts of eggs and nestlings. This camera system uses standard, off‐the‐shelf components, and can easily be altered. The design is not appropriate for humid or dense‐canopy environments because of the inclusion of a laptop and its wired design. However, this design makes the system inexpensive and allows researchers to save, edit, and view nest inspection recordings.     

Alternative stable states in communities with intraguild predation

Intraguild predation (IGP) is a widespread ecological phenomenon in which two consumers that share a resource also engage in a predator-prey interaction. Theory on IGP predicts the occurrence of alternative stable states, but empirical evidence of such states is scarce. This raises the question of whether alternative states are a rare phenomenon that is unlikely to be observed in nature. Here we analyze a model in which the resource exhibits logistic or chemostat dynamics and consumers have saturating (Type II) functional responses. We show that alternative states can arise for a wide range of biological scenarios and that environmental constraints can make their detection difficult. Our analysis identifies three possible combinations of alternative states: (i) IG prey or IG predator, (ii) coexistence or IG predator, and (iii) coexistence or IG prey. Bifurcation diagrams reveal that alternative states are possible over large regions of the parameter space. However, they can be limited to narrow ranges along the resource productivity axis, which may make it difficult to observe the occurrence of alternative states in communities with IGP. Microcosm experiments provide a promising avenue for detecting combinations of asymptotically stable states along a productivity gradient.     

Periplasmic protein EipA determines envelope stress resistance and virulence in Brucella abortus

Molecular components of the Brucella abortus cell envelope play a major role in its ability to infect, colonize and survive inside mammalian host cells. In this study, we have defined a role for a conserved gene of unknown function in B. abortus envelope stress resistance and infection. Expression of this gene, which we name eipA, is directly activated by the essential cell cycle regulator, CtrA. eipA encodes a soluble periplasmic protein that adopts an unusual eight‐stranded β‐barrel fold. Deletion of eipA attenuates replication and survival in macrophage and mouse infection models, and results in sensitivity to treatments that compromise the cell envelope integrity. Transposon disruption of genes required for LPS O‐polysaccharide biosynthesis is synthetically lethal with eipA deletion. This genetic connection between O‐polysaccharide and eipA is corroborated by our discovery that eipA is essential in Brucella ovis, a naturally rough species that harbors mutations in several genes required for O‐polysaccharide production. Conditional depletion of eipA expression in B. ovis results in a cell chaining phenotype, providing evidence that eipA directly or indirectly influences cell division in Brucella. We conclude that EipA is a molecular determinant of Brucella virulence that functions to maintain cell envelope integrity and influences cell division.