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Mesocarnivores play an important ecological role in terrestrial communities. However, there is little information on the abundance of most of these species, which is essential for establishing conservation strategies. The aim of this study was to estimate the population density and temporal variation of species of mesocarnivores in two types of vegetation in southeastern Mexico, and to evaluate the relationship between abundance of each species with vegetation characteristics, human presence, predators, and prey. Using camera traps, we sampled from July 2014–June 2015 and estimated density through the random encounters model, obtaining 640 independent records of 11 species of mesocarnivores. Density in all species did not differ significantly between seasons, although Conepatus semistriatus, Leopardus pardalis, Leopardus wiedii, and Mustela frenata showed significant differences between vegetation types and were present in high densities. We found a positive relationship between abundance of C. semistriatus and Eira barbara with the presence of L. pardalis, but found a negative relationship between E. barbara and human presence. Presence of prey positively affected abundance of L. pardalis and L. wiedii. Density for most mesocarnivores differed from the range known for regions with similar environments. However, estimates for C. semistriatus, E. barbara, M. frenata, and Galictis vittata represent the first approximations of this parameter in Mexico. The high densities that we encountered for some species considered at risk by Mexican law may be due to the good condition of the cloud forest in this region.
Males of the tarantula hawk wasp Hemipepsis ustulata defend individual trees and shrubs growing on ridges and peaks in the Sonoran Desert of Arizona. Territories occupied by males of this wasp species have been monitored in the Usery Mountains of central Arizona for nearly 4 decades. Although previous research indicated that males abandoned their territories by midday, in this study some territories continued to be occupied until as late as 1600h Mountain Standard Time (MST). Territories held into the afternoon included those that were taken early and late in the flight season and which were most-frequently occupied overall. Individual plants that were most likely to attract territorial males during five previous studies were also the most popular territories in 2016. Likewise, many other features of the territoriality of male tarantula hawks have usually been similar during most of the five previous studies of the wasps, including the tendency of larger males to occupy highly ranked territories as residents, the total number of sites occupied by resident males, the mean duration of residency, the total number of male territorial residents during the flight season, and the maximum number of occupied territories on any given day. Results from 2016 provided confirmation that the standard pattern is robust with one partial exception, 1998, a spring in which for unknown reasons the number of tarantula hawk wasps was unusually large and the number of occupied territories was correspondingly large.
In Carlsbad Cavern, New Mexico, a small maternity colony (∼100 individuals) of fringed myotis (Myotis thysanodes) regularly roosts >200 m below the surface of the ground and >1.5 km from the nearest opening to the cavern. With many passageways in the cavern that are closer to surface openings, we investigated why females selected a remote area to bear and raise young. Using radiotransmitters and light tags, we determined that bats traveled 1.8 or 2.1 km, depending on which of only two openings was used to exit the cavern. Air temperatures in the passageway containing the maternity colony and adjacent rooms were the warmest in the cavern, and air moisture also was greater in those areas. Warm and stable air temperatures, high humidity, low predation risk, and infrequent human disturbances were advantages of the roost site. For this colony of M. thysanodes, such advantages seemed to outweigh energetic costs and other disadvantages of commuting to a remote area of the cavern on a nightly basis.
Spatial patterns of sexual size dimorphism for the American black bear (Ursus americanus) from 12 localities in eastern United States were investigated. Forty-four measurements from 371 (187 males and 184 females) adult specimens (≥4.5 years old) were recorded using digital calipers. Males were larger than females for all characters except braincase width and length of m3 for specimens from Virginia. The degree of sexual size dimorphism (SSD) for characters across localities ranged from 4.1–22.5%, with most being from 6.6–17.0%. For 39 of the 44 characters (88.8%), there was no statistically significant difference in degree of SSD across localities, indicating it was approximately the same at each locality. This was further supported by results of principal component analysis. Results followed a similar pattern reported for U. americanus in western North America, which supports a growing generalization for medium-sized and large-sized terrestrial carnivores of a uniform pattern of sexual size variation across geographic space; this is likely due to bioenergetic factors associated with growth and reproduction, with selective pressure responsible for size dimorphism acting uniformly throughout the range of the species.
The deer mouse species group centers around Peromyscus maniculatus and contains four peripherally distributed species. In order to address phylogenetic, taxonomic, and biogeographic questions concerning the westernmost deer mice, we analyzed mitochondrial sequence variation for 174 specimens from California to Washington and compared these to relevant reference specimens. These analyses confirm the genetic distinction of a clade of physiographically bounded deer mouse populations from Southern and Baja California and the close affinity of this clade to the endangered and island-endemic Peromyscus sejugis. In accordance with the phylogenetic species concept and taxonomic priority, we recommend that all populations currently recognized as Peromyscus maniculatus coolidgei (Baja California) and those of Peromyscus maniculatus gambelii from south of the San Francisco Bay and west of the Sierra Nevada mountains be recognized as Peromyscus gambelii. Despite its low level of mitochondrial sequence divergence compared to P. gambelii, the genetic and morphologic distinctness, insular allopatry, and threatened status all argue for the retention of P. sejugis.
Microphyllous and rosetophyllous desert scrub plant communities dominate large parts of the state of Coahuila, Mexico, yet differences in how livestock grazing impacts these two plant communities are not well documented. In order to address this knowledge gap, we assessed livestock impact on plant species composition and vegetation structure in microphyllous and rosetophyllous desert scrublands in this northwestern Mexican state. We collected plant density, frequency, and cover data from sites with and without livestock grazing pressure that were otherwise similar in plant composition. We quantified intersite differences using the importance value index (IVI) and the Bray-Curtis similarity index. The species with the highest IVI for microphyllous scrubland were lechuguilla (Agave lechuguilla), honey mesquite (Prosopis glandulosa), and creosote bush (Larrea tridentata); however, in sites with presence of domestic herbivores, desert willow (Chilopsis linearis) and spiny hackberry (Celtis pallida) also showed high values. Plant species with the highest IVIs in rosetophyllous scrublands were lechuguilla, creosote bush, mariola (Parthenium incanum), and blue grama (Bouteloua gracilis) for both land use types. The Bray-Curtis similarity index between microphyllous desert scrub and rosetophyllous desert scrub was 62%. Moreover, microphyllous scrub with and without livestock had 48% similarity, whereas rosetophyllous scrub sites with and without livestock were 65% similar. Results indicate that livestock grazing significantly modifies plant species composition and vegetation structure in both types of the studied desert scrublands.
Sonoran Desert toads (Incilius alvarius) are known to consume invertebrates, small lizards, other toads, and mice. Here we report an attempt by a Sonoran Desert toad to consume a western desert tarantula (Aphonopelma chalcodes) at Sabino Canyon, Arizona. Despite nearly being completely swallowed, the tarantula was able to escape after a struggle lasting ≥50 s, likely due to defensive bites and urticating hairs.
Extensive research has described the behavioral response of fishes to electrofishing, but few investigations have measured the response of frogs. As electricity continues to be used as a tool to conduct frog and other amphibian surveys, and because frogs inhabit many of the same environments where electrofishing surveys are conducted for fish species, documenting the response of frogs to electricity is important. We measured the voltage gradient and power density thresholds that resulted in immobilization of early life stages of American bullfrog, Lithobates catesbeianus, and Southern leopard frog, Lithobates sphenocephalus, for a range of pulse frequencies (15–120 Hz) and ambient water conductivities (250–1,381 μS/cm). Voltage gradients of 0.40–1.00 V/cm at power densities of 58–1,461 μW/cm3 induced immobility. The lowest power densities causing immobilization were at pulse frequencies of 60 and 120 Hz; more power was required at lower frequencies and in water with a higher conductivity.
We estimated the cranial capacity of 128 Brazilian free-tailed bats, Tadarida brasiliensis, from Oklahoma by filling each cranium with a gelatin suspension. There was no significant difference between the mean cranial capacity of males and females.
Walnut Canyon National Monument, in northern Arizona, was named for its population of Arizona walnut (Juglans major). To increase knowledge of the species' population size and status, the National Park Service conducted a census in 2011–2012 of all Arizona walnut trees in the monument and evaluated their characteristics. The monument contained 2,065 Arizona walnut trees. All size classes were well represented, from seedlings (<1.4 m tall) to mature trees over 15 m tall. The largest individuals had a diameter (at 1.4 m) of 103 cm and a height of 23 m. Over 80% of trees exhibited at least medium vigor (>50% live crown), indicating that trees were healthy across size classes.
The fitness benefits of copulation are evident, but copulation can also incur costs to participating individuals. Many insects copulate for prolonged periods of time during which the female carries or drags the male. This behavior could result in decreased mobility, which in turn might influence the copulating pair's ability to escape from predators and to forage or thermoregulate. Here, I tested how copulation influences movement speed in the common squash bug (Anasa tristis) by measuring average movement speed of unpaired individuals and copulating pairs in an arena trial. Copulating pairs moved significantly slower but, surprisingly, the degree of size disparity between male and female did not influence movement speed. These results suggest that copulation incurs a mobility cost in this species, with potential consequences for survival, but that it is unlikely that mobility costs during copulation lead to selection for smaller male size.
The tendency by individual birds to return to winter sites in subsequent years can be important in assessing the potential influence of habitat changes during the nonbreeding period. We recaptured five Brewer's (Spizella breweri), seven sagebrush (Artemisiospiza nevadensis), and three black-throated (Amphispiza bilineata) sparrows from 1–3 subsequent years at the same winter location following their initial capture. Two Brewer's and one sagebrush sparrow returned to the same winter location at least 4 y after their initial capture. Levels of feather deuterium indicated that birds captured together on winter sites had different breeding ranges. Although individuals of these species returned to specific sites used in previous years, the low recapture rate suggests that wintering individuals may use an itinerant strategy adapted to seasonal food resources.