Effects of habitat destruction and resource supplementation in a predator-prey metapopulation model.

We developed a mean field, metapopulation model to study the consequences of habitat destruction on a predator-prey interaction. The model complements and extends earlier work published by Bascompte and Solé (1998, J. theor. Biol.195, 383-393) in that it also permits use of alternative prey (i.e., resource supplementation) by predators. The current model is stable whenever coexistence occurs, whereas the earlier model is not stable over the entire domain of coexistence. More importantly, the current model permits an assessment of the effect of a generalist predator on the trophic interaction. Habitat destruction negatively affects the equilibrium fraction of patches occupied by predators, but the effect is most pronounced for specialists. The effect of habitat destruction on prey coexisting with predators is dependent on the ratio of extinction risk due to predation and prey colonization rate. When this ratio is less than unity, equilibrial prey occupancy of patches declines as habitat destruction increases. When the ratio exceeds one, equilibrial prey occupancy increases even as habitat destruction increases; i.e., prey "escape" from predation is facilitated by habitat loss. Resource supplementation reduces the threshold colonization rate of predators necessary for their regional persistence, and the benefit derived from resource supplementation increases in a nonlinear fashion as habitat destruction increases. We also compared the analytical results to those from a stochastic, spatially explicit simulation model. The simulation model was a discrete time analog of our analytical model, with one exception. Colonization was restricted locally in the simulation, whereas colonization was a global process in the analytical model. After correcting for differences between nominal and effective colonization rates, most of the main conclusions of the two types of models were similar. Some important differences did emerge, however, and we discuss these in relation to the need to develop fully spatially explicit analytical models. Finally, we comment on the implications of our results for community structure and for the conservation of prey species interacting with generalist predators.

Implications of raccoon latrines in the epizootiology of baylisascariasis.

Raccoons (Procyon lotor) frequently establish defecation sites, termed latrines, on large logs, stumps, rocks, and other horizontally oriented structures/surfaces. These latrines are important foci of infective eggs of Baylisascaris procyonis, a nematode parasite of raccoons which is pathogenic to numerous species of mammals and birds. To examine the role of raccoon latrines in this animal-parasite interaction, we documented animal visitations to raccoon latrines in two large forested tracts and two woodlots in Indiana (USA) during 1994 and 1995. Species richness of vertebrate visitors did not differ between sites or years, but species composition differed by site and year. Fourteen mammal and 15 bird species were documented visiting raccoon latrines. Small granivorous mammals, including white-footed mice (Peromyscus leucopus), eastern chipmunks (Tamias striatus), and tree squirrels (Sciurus carolinensis, S. niger, Tamiasciurus hudsonicus) were the most common visitors to latrine sites. White-footed mice, chipmunks, white-breasted nuthatches (Sitta carolinensis), and opossums (Didelphis virginiana) were photographed foraging on undigested seeds in raccoon feces. Active foraging at latrines also was shown experimentally; seeds embedded in raccoon feces were removed at a greater rate at latrine sites than at nonlatrines. We conclude that raccoon latrines are visited routinely by a variety of vertebrates, especially small granivorous rodents and birds which forage for seeds in raccoon feces, and that raccoon latrines are probable sites of transmission of B. procyonis to susceptible mammals and birds.

Spotted fever group rickettsiae or Borrelia burgdorferi in Ixodes cookei (Ixodidae) in Connecticut.

Immatures and females of Ixodes cookei, a hard-bodied tick, were collected from woodchucks and other mammals in the northeastern United States and examined for spotted fever group rickettsiae and Borrelia burgdorferi. Of the 93 nymphs analyzed by a hemolymph test, 4 (4.3%) harbored rickettsiae. Six (15%) of 40 females were also infected. All infected ticks were collected from woodchucks in Connecticut. Indirect fluorescent antibody staining of midgut tissues from 128 nymphs revealed B. burgdorferi in two (1.6%) ticks, whereas larval and female ticks were negative. Further consideration should be given to I. cookei as a possible vector of spotted fever group rickettsiae or spirochetes that cause Lyme borreliosis.

Identification of volatile components of bobcat (Lynx rufus) urine.

Bobcat (Lynx rufus) urine reduces scent-marking activity of woodchucks (Marmota monax) and feeding activity of snowshoe hares (Lepus americanus) and deer (Odocoileus virginianus, O. hemionus). In order to identify the semiochemicals responsible for these behavior modifications, a dichloromethane extract of the bobcat urine was analyzed by GC-MS. Among the known compounds identified in the extract are phenol, indole, dimethyl sulfone, and 3-mercapto-3-methylbutanol. Compounds for which spectroscopic data are presented for the first time include one sulfide, two disulfides, and two trisulfides. The sulfur compounds are derived from an amino acid,S-(l,1-dimethyl-3-hydroxypropyl)cysteine ("felinine"), which was identified several years ago in the urine of the domestic cat (Felis domesticus).

Aversive responses of white-tailed deer,Odocoileus virginianus, to predator urines.

We tested whether predator odors could reduce winter browsing of woody plants by white-tailed deer (Odocoileus virginianus). Urine from bobcats (Lyra rufus) and coyotes (Canis latrans) significantly reduced browsing of Japanese yews (Taxus cuspidata), and repellency was enhanced when urine was reapplied weekly as a topical spray. Urine of cottontail rabbits (Sylvilagus floridanus) and humans did not reduce damage, suggesting that deer do not respond aversively to odors of nonpredatory mammals or occasional predators with which they lack a long evolutionary association. Bobcat and coyote urine were more effective in tests conducted with eastern hemlock (Tsuga canadensis), which is less palatable to white-tailed deer than Japanese yew. A dichloromethane extract of bobcat urine was as effective as unextracted urine in reducing damage to hemlocks. Testing of the organic components of bobcat urine, particularly the volatile components, may enable identification of the compounds responsible for the repellency we observed.