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Long-tailed weasels (Mustela frenata) are known to feed on mice and voles. However, in the Canadian Prairies, where Richardson's ground squirrels (Urocitellus richardsonii) are abundant (particularly during drought periods), long-tailed weasel predation on these medium-size rodents is poorly documented. In this study, predation by long-tailed weasels on Richardson's ground squirrels was documented from April 2008 to September 2008 in southwestern Saskatchewan during a drought period. I found that Richardson's ground squirrel remains were the dominant food item in percentage of occurrence, volume, and biomass from April to July. In August–September, however, deer mice (Peromyscus maniculatus) and insects became more important. During years of Richardson's ground squirrel abundance, weasels may temporarily switch predation onto these rodents.
To better understand the evolutionary radiation of the Simulium arcticum complex of black flies (Diptera: Simuliidae), we compared the geographic distributions of present-day larvae to their sex-chromosome diversity. We used the 5 known data sets including collections and sex-chromosome analysis from 307 geographic locations of 31 taxa of approximately 20,000 larvae from throughout the geographic range of distribution of the complex, from Alaska, western Canada, and the western United States to southern California, Arizona, and New Mexico. Siblings (reproductively isolated in sympatry) have considerably larger geographic distributions than do cytotypes (not reproductively isolated in sympatry), suggesting that the former may have been in existence longer than the latter. Simulium negativum (the oldest member of the complex), S. brevicercum (standard noninverted sex chromosomes), S. saxosum (sex determination on the X chromosome), and S. arcticum s. s. (IIL-3) share geographic distributions with all other siblings. Notably, 21 of 22 cytotypes share geographic distributions within those of siblings. Cytotypes are almost always discovered within the geographic distributions of siblings, suggesting that the former might be arising sympatrically.
Roots play a critical role in carbon storage, carbon cycling, and resource acquisition in dryland ecosystems, yet their distribution and production patterns are poorly understood. We aimed to compare the vertical and horizontal distribution of roots of the dominant plant functional types across 3 dryland ecosystems in the western Great Plains of the United States. We collected consecutive soil cores from directly under plants to 29 cm away from the center of plant individuals (horizontal plane), to a 20-cm depth (vertical plane). Across the 3 ecosystem types, grass root biomass decreased with depth and, for the sagebrush steppe, at a distance beyond 6.5 cm from the center of the plant. At the 10–20 cm depth increment, there was no horizontal pattern in root biomass. Uniformity in root biomass in the 10–20 cm depth and at distances >6.5 cm from the plant center is best explained by the overlap of roots of individual and neighboring plants to maximize belowground resource uptake. There was much lower root biomass in the surface 20 cm adjacent to shrubs than adjacent to grasses in the sagebrush steppe, and while grass root biomass decreased significantly with depth and distance as described above, shrub roots were uniform in both planes. Our study confirms that root distribution in drylands differs among plant functional types, with grasses exploiting surface soils both horizontally and vertically to capitalize on surface resources, and shrubs capitalizing less on those resources.
Sylvilagus audubonii (desert cottontail) and Lepus californicus (black-tailed jackrabbit) occur in sympatry in the southwestern United States and northern Mexico. During the daytime, both species occupy shallow excavations under shrubs known as forms. Comparisons of form and shrub characteristics between the 2 species can provide insights into connections between body size, physiology, and behavior. I examined forms of the 2 species in the Chihuahuan Desert in southern New Mexico, USA, from 2014 to 2016. In response to temperature, S. audubonii varied the structure of its forms and dug burrows, whereas L. californicus did not. Sylvilagus audubonii forms were most commonly located in the centers of patches of shrubs, whereas L. californicus forms were most commonly on the edges of patches. Overhead canopy depth and exposure to direct sunlight were not different between the 2 species, but canopy heights were less at S. audubonii forms than at L. californicus forms. Sylvilagus audubonii individuals were less visible to predators than L. californicus individuals at predator eye level in all directions, and the horizontal extent of canopies was greater at S. audubonii forms than at L. californicus forms in all directions except to the left side. An asymmetry was evident in the exposure of S. audubonii to predators, which may be the result of brain lateralization. Although distance to nearest neighbor shrubs was not different between the 2 species, open space around L. californicus forms was greater than around S. audubonii forms. Lepus californicus forms were located under Larrea tridentata in proportion to its availability and more often than forms of S. audubonii, which were located under L. tridentata less often than it was available. These observations are consistent with concordant ensembles of adaptations in which S. audubonii is smaller, more sensitive to heat, and more inclined to hide rather than run from predators in comparison with L. californicus.
For population studies that rely on aural or visual observations of individuals, methods that induce a detectable response can greatly improve sample sizes and reduce costs. Numerous authors have reported improved detections using broadcast surveys in forested areas for various species of raptors; however, to our knowledge, none have attempted to quantify the effects of broadcast surveys on the detection probability (p) in the context of an occupancy study for multiple species. Our objective was to determine whether broadcasting conspecific and heterospecific calls (broadcast surveys) would increase p of raptor species compared to passive surveys. This comparison was accomplished by estimating p during both types of surveys using a multiscale occupancy framework. We conducted 8400 surveys for Cooper's Hawk (Accipiter cooperii), Swainson's Hawk (Buteo swainsoni), White-tailed Hawk (Geranoaetus albicaudatus), Harris's Hawk (Parabuteo unicinctus), Red-tailed Hawk (Buteo jamaicensis), and Great Horned Owl (Bubo virginianus) in 2015 and 2016 in south Texas. We conducted 10-min passive surveys in both years, 10-min broadcast surveys in 2015 including calls from each of the target hawk species, and 10-min broadcast surveys in 2016 using calls from Great Horned Owls. Our results suggest that p is improved with multiple-hawk broadcast surveys (0.16, SE 0.04) over passive surveys (0.04, SE 0.02) for Harris's Hawks; p was not affected in broadcast surveys for the other hawk species considered. Great Horned Owls had a higher p during broadcast surveys using Great Horned Owl calls (0.35, SE 0.04) than during passive surveys (0.19, SE 0.02). Our results do not support the use of broadcast surveys to improve the detection probability of multiple species of hawks. However, our results do indicate that using broadcast surveys for occupancy studies focused on Harris's Hawks or Great Horned Owls should significantly reduce the effort required over passive surveys, resulting in improved power and reduced costs.
Scutellaria mexicana (Lamiaceae) is a common shrub in the Mojave and northern Sonoran Deserts in North America. The plant produces small tubular and bilabiate flowers that are nototribic by enclosing 2 pairs of stamens and a style within a hooded upper corolla lip. I investigated the pollination of the species in southern Nevada during April 2018 by aspirating insects from flowers. I estimated amounts of S. mexicana pollen on the front of the head and dorsum of the thorax, determined proportions of conspecific pollen on the head, thorax, and middle and hind legs, and examined correspondence between measurements of insect and flower structure. All insects collected on flowers were similarly sized bees in Anthophora (Apidae), mostly comprising A. coptognatha females, followed by A. centriformis males and females. Bees landed on flowers and fed on nectar with the front of the head against lobes that extended laterally from the base of the upper corolla lip. Large and varying amounts of conspecific pollen were carried on the head and thorax of bees, consistent with S. mexicana's nototribic flowers. Bees appeared specific to the plant because they carried high proportions of S. mexicana pollen. Proportions of conspecific pollen on bees differed among collection sites, likely due to different floral compositions. Lower proportions of conspecific pollen on the legs compared with the head or thorax indicated that pollen from plants other than S. mexicana was more likely to be transferred to the legs by bees of both sexes and transported to larvae by females. The length of Anthophora's long glossa corresponded to the depth of the corolla and the availability of nectar. The vertex of the head and anterior dorsum of the thorax of bees feeding on nectar would align with the anthers and stigma on the flowers. Scutellaria mexicana in southern Nevada appears to be dependent on Anthophora bees for pollination.
The geographically widespread mayfly genus Baetis occurs from the subarctic to tropical regions of the world. Many of the 20 described Baetis species in North America are known to show cryptic species diversity. However, studies of Baetis that have examined morphology and genetic diversity have found mixed results in terms of cryptic species, with some studies indicating a complex of related species and others suggesting a single widespread species. We used Bayesian analyses, intra- and interspecific genetic diversity values, and median-joining haplotype networks to compare cytochrome oxidase I (COI) sequences from Baetis specimens from parts of northern and southern California (n = 742). Our results suggest that genetic diversity at the COI gene region in populations from northern California supports the diversity indicated by morphology (Baetis tricaudatus and Baetis adonis); however, populations in southern California exhibit more genetic diversity than indicated by morphology alone (DNA divergence > 1%), which suggests cryptic species diversity. The putative species that was morphologically and genetically identified as Baetis tricaudatus was the only taxon that occurred in both regions. No haplotypes were shared between regions. Intraspecific diversity within putative species from northern California was >1%. In contrast, intraspecific diversity within species from southern California was always <1%. Such discrepancies highlight the need for locally derived reference libraries in using next-generation sequencing or environmental DNA as a method to examine genetic diversity.
We provide the first documentation of morphological variation in the lower first molar (m1) of Lemmiscus curtatus from southern Canada. A total of 370 specimens were obtained from owl pellets taken from 4 localities in southern Saskatchewan. The 4 most common morphotypes are, in order of descending relative abundance, molars with 5 closed triangles and a well-developed but widely open sixth triangle, molars with 5 closed triangles and a sixth triangle that is pinched at the confluence of the anterior cap, molars with 5 closed triangles and incipient closure of the sixth triangle from the anterior cap, and specimens with 6 closed triangles. As is true of other modern populations of L. curtatus, the samples from Saskatchewan include no morphotypes with only 4 closed triangles. This collection is notable for the relatively high proportion of specimens with pinched, incipient, or full closure of a sixth triangle on the m1, and it also highlights the complex dynamics of dental evolution in arvicoline rodents.
Despite the critical need to improve degraded herbaceous understory conditions in many semiarid ecosystems, the influence of soil properties on seedling emergence of species seeded in shrubland plant communities is largely unexplored. We evaluated emergence patterns of 6 restoration species in soils from wyomingensis (i.e., Wyoming big sagebrush, Artemisia tridentata ssp. wyomingensis [Beetle & A. Young] S.L. Welsh) and vaseyana (i.e., mountain big sagebrush, A. t. ssp. vaseyana [Rydb.] Beetle) plant communities that differed in soil texture, soil organic matter content, and soil water-holding capacity. We conducted 2 separate experiments that regularly wetted soils to standardized soil water potentials (i.e., field capacity; −0.03 MPa) and allowed differences in evaporation to create distinct wet-dry watering pattern cycles over a 26–29 d period. Our objectives were to compare soil attributes of wyomingensis and vaseyana soils, evaluate whether emergence patterns of restoration species vary within these soils, and determine how these patterns are altered by soil water-content levels. We found differences in soil texture and organic matter between soils and thus soil water-holding capacity: finer-textured vaseyana soils held roughly twofold more water than coarse-textured wyomingensis soils. Seeds in vaseyana soils were exposed to fewer wet-dry cycles compared to wyomingensis soils because of the greater capacity of vaseyana soils to retain water. Restoration species also collectively exhibited greater emergence in vaseyana soils than in wyomingensis soils, yet emergence patterns were vastly different among species, and differences between soils became more pronounced under low soil water for only 2 species. We conclude that the manner in which soils and water uniquely influenced emergence patterns provides new insights into species suitability for restoration sites and how inherent soil differences may constrain seeding success.
In this paper I report on the poorly known terrestrial mollusk fauna of Great Basin National Park (Snake Range) of the central Great Basin, USA. Mollusk species and numbers were recorded according to habitat affinities defined by a combination of rock type, geomorphology, plant communities, and water sources. A total of 6892 individuals representing 18 species of land snails and 1 species of slug were identified from 50 stations within GBNP during the period of spring 2014 through summer 2016. Mollusks were surveyed by 186 soil/litter samples and 1755 min of hand searching. Twelve habitat types included 2 xeric limestone/dolomite environments with conifer/aspen woodlands and no perennial waters (10 species in woodland litter and 15 species in rock slides below cliff faces). Two habitats dominated by granite/quartz rock with conifer/aspen woodlands and perennial streams supported 12 species in woodland litter and 13 species in rock slides. Eight species were recorded from a lower-elevation riparian habitat with cottonwood and shrubs. Two high-elevation habitats (approximately 3000 m) without perennial waters and dominated by bristlecone pine supported 1 species in limestone and 3 species in granite/quartz. A single high-elevation habitat (2800 m) of xeric pinyon pine/mountain mahogany and granitic/quartz rock supported 4 species. Two lower-elevation habitats (1800 m) supported 2 species in a sagebrush steppe, while no mollusks were found in pinyon pine/Utah juniper woodland. Two localized mesic habitats were associated with boggy streamsides and natural springs and supported 11 species each. The single species of slug Deroceras laeve and a species of succineid snail are restricted to these 2 habitat types. The 4 most common species of land snails (Pupilla hebes, Vallonia cyclophorella, Euconulus fulvus, and Vitrina pellucida) were present in 7 to 9 of the habitat types and represented 70% of the individual shells recovered. Taxonomic and biogeographical notes are included to allow for a better understanding of the species present in GBNP and the relationship of these species to the larger distribution of the terrestrial mollusks within Nevada and the Great Basin.
The hydrophyte Allenrolfea occidentalis (S. Watson) Kuntze (iodinebush) is a halophytic shrub of the arid southwest that is listed as a facultative wetland species on the National Wetland Plant List. This rating means that the species is usually a hydrophyte but occasionally is found in uplands. We tested for genetic (ecotypic) differences between plants sampled from wetlands versus uplands. We used the technique of genotyping by sequencing to generate data from 132 plants from 30 locations representing both wetland and upland occurrences for over 1300 loci. Analyses indicated that the strongest genetic signal is from differences in geographic distribution: samples that are in close geographic proximity tend to be more similar genetically regardless of whether they occur in wetland or upland locations. We detected no effect of habitat on overall genetic structure, and we found only 2 (of the 1381) loci with a positive association between genotype and habitat; in both cases the association was very weak. We infer that A. occidentalis occurrences near or in wetlands are not influenced by significant differences in genetics, and we find no evidence for wetland and upland ecotypes of this species.
Multiple mechanisms have been suggested to facilitate coexistence among species of burying beetles, including differential use of habitat and food resources. Nicrophorus marginatus and Nicrophorus guttula are similarly sized burying beetles that co-occur in many parts of their range. We used observations to quantify and compare their diel activity patterns and tested for possible niche partitioning between the species. We monitored activity of individuals of each species over four 24-h periods. Both species exhibit bimodal activity patterns with peaks of activity in the morning and evening. Nicrophorus guttula is active earlier in the morning and later in the evening than N. marginatus. This difference suggests possible temporal niche partitioning and may represent an important mechanism for the coexistence of these burying beetle species.
We report what we believe is the first documented observation of Island Scrub-Jay (Aphelocoma insularis) copulation behavior. We compare our observations to the behaviors of other Aphelocoma jays with the aim of identifying potential species-specific elements. There are observable differences between the precopulatory display of the Island Scrub-Jay and that of more distantly related Aphelocoma jays. The display of Island Scrub-Jay and that of the closely related California Scrub-Jay (Aphelocoma californica) are very similar despite the species being isolated from each other for approximately 1 million years.
During the summers of 2015 and 2018, we observed predation on Foothill Yellow-legged Frogs (Rana boylii) by a giant water bug (Abedus indentatus), a California Red-legged Frog (Rana draytonii), and a Diablo Range Gartersnake (Thamnophis atratus zaxanthus) adjacent to 3 separate isolated pools along intermittent reaches of Coyote Creek, Santa Clara County, California, USA. To the best of our knowledge, our observations provide the first published record of California Red-legged Frog and giant water bug preying upon Foothill Yellow-legged Frogs. As pool habitat contracts over the course of the dry season, locally abundant Yellow-legged Frogs may be increasingly vulnerable to predation from a suite of aquatic and terrestrial predators.