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The array of island-like mountains that characterizes the Great Basin has long been a model system for studying the effects of past and present climate change on distributions of montane mammals. One of the smallest of these mountains is the Pilot Range (Nevada/Utah). This range has relatively few species of montane mammals, presumably because of its small size and the fact that it was isolated by the waters of Lake Bonneville during much of Pleistocene. One of the species previously assumed to be absent in the Pilot Range is the yellow-bellied marmot (Marmota flaviventris). On 23 May 2016, I documented marmots living in the Patterson Pass area of the Pilot Range. This discovery shows how the use of high-resolution satellite images and geological maps combined with a good understanding of the species' habitat provides an excellent opportunity to confirm the presence or accurately infer the absence of a species in a remote, rugged location.
Age-based differentiation in the timing of avian migration can influence subsequent habitat use and, therefore, reproductive success. Over 2 breeding seasons, we compared arrival dates, pairing success, and fledging success for second-year (SY) and after-second-year (ASY) federally endangered Golden-cheeked Warblers (Setophaga chrysoparia) occupying areas of low (n = 9 sites) and high (n = 10 sites) warbler density. Male warblers arrived on low-density sites on average 6 days later (11 March) than high-density sites (5 March). Male warblers that established territories on low-density sites tended to be younger than male warblers that established territories on high-density sites. Overall pairing and fledging success were similar across low- and high-density sites, but overall pairing and fledging success were lower for SY males compared to ASY males; no SY birds fledged young on low-density sites. We found no difference in pairing or fledging success for ASY males at low- and high-density sites. For some species, habitat that supports fewer birds may be of lower quality. However, warblers in our study area fledged young at low- and high-density sites. As such, low-density sites may fill an important role in conservation efforts for this species.
Roads associated with energy development have fragmented much of the Uinta Basin, the Colorado Plateau in general, and other areas of western North America. Beyond reducing available habitat, spreading exotic species, and creating barriers to dispersal, unpaved roads also increase dust loads on plants and pollinators, which may reduce plant growth and reproduction. We studied the effects of an unpaved road on reproduction of an endangered Utah endemic shrub. We measured the size and reproductive output of 156 plants and the dust deposition in plots at increasing distances from the road. We also hand outcrossed 240 flowers from 80 plants to help determine if any reduced reproduction was due to pre- or postpollination mechanisms. Additionally, we experimentally dusted 3 leaves on 30 plants (n = 90) and measured stomatal conductance pre-dust and post-dust. We also dusted 3 flowers on 10 plants (n = 30) prior to hand pollination and measured fruit set. Generalized linear mixed models were used to examine the relationship between reproduction and dust deposition. When controlling for plant size and distance from the road, fruit set was negatively correlated with increasing levels of dust deposition (F1, 15 = 5.26, P = 0.036). The number of seeds per plant, mean plant seed weight, and the proportion of hand-pollinated flowers that set fruit were also negatively correlated with dust, although not significantly. Dusting significantly reduced stomatal conductance (F1, 58 = 87.56, P < 0.001). Eighty percent of hand pollinated flowers (24 of 30) set fruit after dusting. These results demonstrate that road dust reduces H. suffrutescens reproduction, although the mechanisms are not clear. Although dust negatively affected physiological processes, hand-pollination results suggest that dust might be disrupting pollination. This study documents the effects of road dust on the reproduction of an endangered shrub in Utah's Uinta Basin and highlights the need for further research into the effects of roads and dust on nearby plants.
We evaluated the thermal regime and relative abundance of native and nonnative fish and invertebrates within Kelly Warm Spring and Savage Ditch, Grand Teton National Park, Wyoming. Water temperatures within the system remained relatively warm year-round with mean temperatures >20 °C near the spring source and >5 °C approximately 2 km downstream of the source. A total of 7 nonnative species were collected: Convict/Zebra Cichlid (Cichlasoma nigrofasciatum), Green Swordtail (Xiphophorus hellerii), Tadpole Madtom (Noturus gyrinus), Guppy (Poecilia reticulata), Goldfish (Carassius auratus), red-rimmed melania snail (Melanoides tuberculata), and American bullfrog tadpoles (Lithobates catesbeianus). Nonnative fish (Zebra Cichlids and Green Swordtails), red-rimmed melania snails, and bullfrog tadpoles dominated the upper 2 km of the system. Abundance estimates of the Zebra Cichlid exceeded 12,000 fish/km immediately downstream of the spring source. Relative abundance of native species increased moving downstream as water temperatures attenuated with distance from the thermally warmed spring source; however, non - native species were captured 4 km downstream from the spring. Fish diseases were prevalent in both native and nonnative fish from the Kelly Warm Spring pond. Clinostomum marginatum, a trematode parasite, was found in native species samples, and the tapeworm Diphyllobothrium dendriticum was present in samples from nonnative species. Diphyllobothrium dendriticum is rare in Wyoming. Salmonella spp. were also found in some samples of nonnative species. These bacteria are associated with aquarium fish and aquaculture and are generally not found in the wild.
Conservation practitioners often rely on areas designed to protect species of greatest conservation priority to also conserve co-occurring species (i.e., the umbrella species concept). The extent to which vertebrate species may serve as suitable umbrellas for invertebrate species, however, has rarely been explored. Sage-grouse (Centrocercus spp.) have high conservation priority throughout much of the rangelands of western North America and are considered an umbrella species through which the conservation of entire rangeland ecosystems can be accomplished. Harvester ants are ecosystem engineers and play important roles in the maintenance and function of rangeland ecosystems. We compared indices of the abundance of western harvester ants (Pogonomyrmex occidentalis) and Greater Sage-Grouse (Centrocercus urophasianus) at 72 sites in central Wyoming, USA, in 2012. The abundance of harvester ant mounds was best predicted by a regression model that included a combination of local habitat characteristics and the abundance of sage-grouse. When controlling for habitat-related factors, areas with higher abundances of sage-grouse pellets (an index of sage-grouse abundance and/or habitat use) had higher abundances of ant mounds than areas with lower abundances of sage-grouse pellets. The causal mechanism underlying this positive relationship between sage-grouse and ant mound abundance at the fine scale could be indirect (e.g., both species prefer similar environmental conditions) or direct (e.g., sage-grouse prefer areas with a high abundance of ant mounds because ants are an important prey item during certain life stages). We observed no relationship between a broad-scale index of breeding sage-grouse density and the abundance of ant mounds. We suspect that consideration of the nonbreeding habitat of sage-grouse and finer-scale measures of sagegrouse abundance are critical to the utility of sage-grouse as an umbrella species for the conservation of harvester ants and their important role in rangeland ecosystems.
Piñon-juniper woodland is expanding across much of western North America. In the Great Basin, woodland expansion has encroached on native shrublands, threatening species that have close associations with the sagebrush ecosystem. Piñon-juniper woodlands also harbor great biodiversity, and the response of woodland specialists to expansion has been less well studied than that of shrubland specialists. Here, we use occupancy and abundance modeling, accounting for imperfect detection, to assess habitat use of a woodland specialist, the piñon mouse (Peromyscus truei). Our study occurred in the Toiyabe Range of central Nevada, an area P. truei is thought to have recently colonized. Understanding habitat use at an expanding range margin can have important implications for dispersal-mediated woodland expansion. Peromyscus truei was documented in a wide range of conditions, including nonwoodland and woodland habitats, across the latitudinal and elevational extent of the mountain range. Occupancy models suggest that P. truei occurrences are most associated with the presence of piñon pine. For abundance, our global model was the best supported, indicating that no one environmental factor or set of factors considered were found to structure abundance. Chi-square tests indicate that use of woodland versus nonwoodland habitats by P. truei is not structured by age or sex. Although P. truei was found in a range of habitat types, we cannot conclude whether it is more appropriate to characterize this species as a habitat generalist, or whether postcolonization abiotic and biotic filtering is not yet complete. Research on woodland specialists at expanding local and landscape-scale range margins provides a unique opportunity to study how habitat selection and ecological filtering impact community assembly under environmental change.
Phoradendron juniperinum (Viscaceae) is a dioecious, parasitic plant of juniper trees ( Juniperus [Cupressaceae]) that occurs from eastern California to New Mexico and into northern Mexico. The species produces minute, spherical flowers during early summer. Dioecious flowering requires pollinating insects to carry pollen from male to female plants. I investigated the pollination of P. juniperinum parasitizing Juniperus osteosperma trees in the Cerbat Mountains in western Arizona during June–July 2016. I examined pollen from male flowers, aspirated insects from female flowers, counted conspecific pollen grains on insects, and estimated floral constancy from proportions of conspecific pollen in pollen loads. The tricolpate pollen from P. juniperinum was subangular in shape with open furrows in polar view and oval-spherical in shape in equatorial view. Most insects on flowers were small (<3 mm in length). Insects carrying conspecific pollen to female flowers included 6 species of Hymenoptera in 6 families and 6 species of Diptera in 5 genera and 4 families. Conspecific pollen was found on 41% of the insects, with only 18% carrying >1 grain, and numbers of grains on insects did not differ among the species collected. Phoradendron juniperinum was most likely pollinated by 2 species of flies in Hippelates (Chloropidae) and Desmometopa (Milichiidae) and 1 species of parasitic wasp in Apanteles (Braconidae). Insects in these genera were widespread and frequently collected, with half of specimens carrying conspecific pollen that comprised most of the pollen load. Other Diptera carrying conspecific pollen included 1 species in Olcella (Chloropidae), 2 species in Mythicomyia (Mythicomyiidae), and 1 species in Scatopsidae. Other Hymenoptera with conspecific pollen included 1 species of bee in Lasioglossum (Halictidae), 1 species of wasp in Parancistrocerus (Vespidae), and 3 species of parasitic wasps in Chalcidoidea. Minute flies, such as Tephritidae or Chloropidae, are the most common pollinators among P. juniperinum and the 2 other examined species of Phoradendron (P. californicum and P. coryae). Pollination of Phoradendron likely differs among species due to different host plants, plant communities, and flowering seasons.
Dipteran pollinators are important in the successful reproduction of many plants, yet are less studied than other groups. We know that these insects affect the biodiversity of natural landscapes, yet much remains unknown about the extent of their influence in pollination systems and flight seasons. In this study, we collected hover flies (Diptera: Syrphidae) with 3 Malaise traps at a midelevation site in central Utah throughout the flies' flight season of 2015. We collected 27 genera and 48 species in our traps. We determined seasonal flight times by collecting at weekly intervals throughout the frost-free year. Abundance of all hover flies peaked twice, in June and September, showing a bimodal distribution. We noted a drop in overall abundance during the hottest months of July and August. Species diversity and richness also peaked in June and September. We calculated species richness estimators, which suggest that more than 60 species make up the total assemblage at the study site. Local museum records show 28 species caught in similar locations near the sample site before the year 2000 that were not collected during our study.
During the last century, populations of the endangered Razorback Sucker (Xyrauchen texanus) have declined in the Colorado River Basin. Dramatic changes in habitat resulting from altered flow regimes and the presence of nonnative fishes were likely major factors contributing to this decline. Since 1996, studies in Lake Mead have resulted in the discovery of 4 areas where wild Razorback Suckers were spawning; all of these locations have tributary or wastewater inflows. Since the Lake Mead Razorback Sucker population has persisted near these prominent inflow areas, we hypothesize that complex inflow areas with vegetative cover and turbidity provide important habitat for the species. In 2011, Razorback Sucker investigations at the Lake Powell—Colorado River inflow and the Lake Powell—San Juan River inflow were initiated and, similar to Lake Mead, we found large numbers of Razorback Suckers using both of these inflow areas. Multiple age classes of Razorback Suckers were found in Lake Powell, along with spawning activity and Razorback Sucker larvae, but wild recruitment was more difficult to document due to the large numbers of fish stocked upstream into the Colorado and San Juan Rivers that may have moved into the reservoir. Since Razorback Suckers are present at the prominent inflow areas of Lakes Mead and Powell, we compared reservoir-specific research and monitoring data to highlight the potential for Razorback Sucker recruitment and to promote the importance of these areas for species conservation and recovery. Our research suggests that inflow areas in Lakes Mead and Powell may provide the criteria necessary for Razorback Suckers to reproduce, grow, and persist.
Cheatgrass (Bromus tectorum), Russian thistle (Salsola kali), and tall tumblemustard (Sisymbrium altissimum) are nonnative plants widely distributed throughout the desert and shrubsteppe communities of the western United States. The impact of these invaders on plant community structure, form, and function has been well documented, but investigations determining the impacts of this cumulative invasion on terrestrial vertebrates have not been undertaken. Our objective was to assess community-level rodent responses to changes in plant community features, with an emphasis on dominance of invasive plant species. We sampled rodent and plant communities in the Great Basin Desert (Utah) over 4 years. Using estimates of rodent species richness and average nightly captures (relative abundance) as our response variables, we developed generalized linear mixed models (GLMMs) to determine the effects of invasive species cover. We found that rodent richness decreased with increasing abundance of invasive plant cover. Contrary to other studies, there was a nonlinear relationship between invasive species cover and rodent abundance, where rodent captures increased with invasive plant cover, reached a threshold, and then exhibited a negative response. This nonlinear relationship provides support for the intermediate disturbance hypothesis and suggests that moderate levels of plant invasions, by way of bolstering rodent abundance and rodent biomass, could have bottom-up effects (i.e., positively influencing species that predominantly prey upon rodents). Our findings contradict previous findings on plant invasions in arid portions of the western United States and suggest that the species comprising or dominating a given rodent community may determine the impact of plant invasions.
Feral horses are widespread in the western United States, with the majority of feral horse herds found in the Great Basin. There is a federal mandate to manage these herds in order to maintain “ecological balance”; however, understanding of the specific effects of feral horse grazing on rangeland plant communities in this region is incomplete. To address this research gap, we utilized long-term grazing exclosures and fenceline contrasts to evaluate the impacts of feral horses on several plant community variables (diversity, richness, dominance, and biomass) and species composition. Because the effects of grazing can vary with site precipitation and productivity, we selected 5 sites from 4 different rangeland types (Great Basin Desert, Colorado Plateau, Rocky Mountain grassland, and mixed grass prairie) that spanned a mean annual precipitation gradient of 229 to 413 mm. Our results did not reveal a significant effect of feral horse grazing on plant community composition, species richness, diversity, evenness, or dominance. In contrast, total aboveground herbaceous biomass and grass biomass were significantly reduced with feral horse grazing, but these effects did not vary with mean annual precipitation. Our results suggest that, at least at the sites we studied, feral horses have affected the plant community by reducing herbaceous biomass but have not caused plant community shifts. Additional multisite studies, preferably with standardized exclosures and larger sample sizes, would increase our understanding of feral horse grazing effects and inform management of feral horse herds in the western United States.
The eastern cottontail rabbit (Sylvilagus floridanus; ECR) is highly adaptable to human activities and widely distributed across the Yucatan Peninsula. However, the eastern part of the peninsula, where the Mexican state of Quintana Roo is located, had only marginal records. Herein, we report the collection of one individual and the observation of 7 different individuals of the ECR in northeastern Quintana Roo. These records increase the range of the species by 66 km into the eastern portion of the Yucatan Peninsula. The absence of previous records of the species—even though the mammalian fauna of the region has been surveyed both historically and recently—probably indicates that the species has expanded its range. Further research is required to determine factors that contribute to the species' range expansion as well as its effects on other species.
A specimen of the Inyo shrew, Sorex tenellus, was collected in piñon-juniper woodland at 2017 m elevation in Granite Creek Canyon, Deep Creek Range, Juab Co., Utah. This is the easternmost record for this species and the first record for Utah.