The number of desert bighorn sheep (Ovis canadensis mexicana) in Pusch Ridge Wilderness (PRW), Santa Catalina Mountains, Arizona has declined to between 50 and 100 animals. Sheep have restricted movements to the southwest corner of PRW. I developed a model based on nitrogen (N) content of forage and forage quantity to measure seasonal changes in nutritional carrying capacity of sheep use areas in PRW. Forage based estimates of animals numbers were greater for April to September than for October to March. My study suggests that forage is not limiting desert bighorn sheep in PRW and illustrates the potential to support more desert bighorn sheep in PRW than the current population. Seasonal fluctuations in range productivity should be examined in relation to human disturbances proximal to desert bighorn sheep habitat and fire management programs for PRW.

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The interaction between Xylocopa californica and Chilopsis linearis was used to test the hypothesis that nectar robbing is costly to plants. No evidence for these costs, either in terms of decreased pollination or increased energy demands, was found. In fact, the mean number of seeds per fruit and the mean individual weight of seeds per fruit was higher from fruits that developed from robbed flowers than from fruits that developed from unrobbed flowers, indicating that the presence of Xylocopa californica enhanced pollination. Chilopsis linearis pollen was isolated from the tips of the abdomens of robbing Xylocopa californica and it was determined that these bees could be transferring pollen from flower to flower as they position themselves to rob. This association was found to be one of mutual benefit rather than one of exploitation.

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Disturbance events can alter habitat properties, leading to species displacement, isolation and/or local extinction. In addition, introduced species have been recognized as a threat to biodiversity of native species. Understanding the interacting impacts of fire on native and introduced wildlife species, and the influence on a native species of competition with an introduced species after ecosystem change is critical. Tree squirrels are indicators of forest health; we used two species to determine thresholds and assess behavioral responses to determine adaption to habitat alterations. We studied native Arizona gray squirrels (Sciurus arizonensis), which are believed to favor riparian habitat, and introduced Abert's squirrels (S. aberti), which prefer open parklike ponderosa pine (Pinus ponderosa) in the Santa Catalina Mountains, Arizona, USA. We examined how native but reportedly declining Arizona gray squirrels and introduced Abert's squirrels use areas within widespread fires that burned the study area in 2002-3. Fires burned in a mosaic pattern of unburned, low, moderate, and high burn severity patches. To determine how fire may affect squirrel habitat and behavior, we examined how fire altered habitat use and occupancy, and used distance sampling to determine squirrel abundance, distribution and use within a mosaic of burn severities. Occupancy and habitat use indicate that introduced Abert's squirrels are better adapted to post-fire conditions whereas native Arizona gray squirrels may be adversely impacted by fire disturbance. Our results suggest that Arizona gray squirrel populations may be locally imperiled due to post-fire habitat alteration and loss exacerbated by competition with Abert's squirrels. Abert's squirrels predominantly occupied unburned ponderosa pine and mixed conifer zones with open understories. In contrast, Arizona gray squirrels were documented at only four sites and primarily occupied unburned to low burn riparian areas with dense understories. Abert's squirrels predominately nest and feed in unburned coniferous areas whereas Arizona gray squirrels nest in unburned to low burn nonconiferous areas. Arizona gray squirrels have a reduced distribution and potentially in decline but only remain at lower elevations on the Santa Catalina Mountains. Fire management and restoration efforts should include examination of the differential impacts of fire on native and invasive species.