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We studied the seasonal fluctuations in the eviscerated body weight, liver, fat bodies, and volume of food eaten in a population of viviparous lizard Sceloporus torquatus torquatus inhabiting the southern part of the Valley of Mexico. Observed changes in the mass of fat bodies of females suggest that most of the stored lipids in these structures are used for maintenance during the two driest months of the year. During the dry season, females consumed nearly seven times less food than during the rainy season, and their physical condition (mean eviscerated weight) was much lower in April (the driest month) than in May (start of the rainy season). Liver mass in females was higher during the rainy season than in the dry period. Males stored fewer lipids in the fat bodies than did females. However, the stored energy in these structures may be important at the beginning of the dry season to support activities related with their reproductive behavior and to survive during the driest months of the year. There were no significant monthly changes in carcass mass or quantity of food eaten by males. In contrast, the liver mass of males changed significantly during the study year although the biological significance of these changes is unclear.
Human modification of the environment can result in the fragmentation and isolation of natural populations. If isolated populations are small, they may experience higher probabilities of extirpation from genetic, demographic, and environmental effects. One approach for managing fragmented and isolated populations is facilitated migration in which individuals are moved between habitat fragments. Here we report on a study of a single system in which we followed the genetic and population consequences of facilitated migration. We moved a small number of pupfish (Cyprinodon nevadensis pectoralis) from one small spring into another small spring that had become isolated as a consequence of human modification of surface hydrology. We followed the fate of immigrant, resident, and admixed fish over multiple generations using molecular identification of individuals and mark-recapture methods. The mark-recapture data revealed that survival probabilities for admixed individuals were about 20% greater than those for the original resident fish. Furthermore, there was a steady increase in the proportion of admixed individuals, suggesting that immigrant alleles spread through the population consistent with the estimate of relative fitness. Overall, the results suggest facilitated migration can have restorative effects over the course of very few generations, and these results, in the context of other studies, suggest facilitated migration is likely to be an effective strategy for managing populations that have become isolated as a consequence of human modification of landscapes.
We characterized the distribution of migrating birds in high-elevation forested habitat in north-central New Mexico during spring migration. In contrast to many other stopover studies in the American southwest, we focused on a range of forested upland habitats rather than lowland riparian corridors. We censused birds in piñon-juniper woodland, ponderosa pine forest, and spruce-fir forest to ascertain the effects of mountain range and habitat on abundance and richness of Nearctic-Neotropical migrants. We detected 28 migratory species and found that migrants were associated with the two southern ranges (Manzano and Sandia mountains) significantly more than with the northernmost Sangre de Cristo Mountains, and Nearctic-Neotropical migrants were more abundant and species-rich in piñon-juniper and ponderosa pine habitats. The nonrandom distribution of migrating birds in this study, and the potential for climate-driven habitat change and anthropogenic use of forested habitat to affect migrating birds, indicates that upland forest in the southwestern United States deserves more research during the migratory period.
Over the past decade, large populations of invasive quagga mussels (Dreissena rostriformis bugensis) have become established in reservoirs along the lower Colorado River in the southwestern United States. We were interested in whether genetic patterns among these populations have changed during continuing expansion and establishment, and how current genetic patterns in reservoirs along the lower Colorado River would compare with other invasive D. rostriformis bugensis populations. We examined the neutral genetic structure among six populations from different reservoirs along the lower Colorado River. We genotyped individual quagga mussels at 10 microsatellite DNA loci to analyze patterns of genetic diversity and population structure. As in past studies of some of these same populations, overall genetic divergence among populations was negligible and no single reservoir population was significantly differentiated from the overall group. Some populations did exhibit significant, if slight, pairwise genetic differentiation, and there was a moderate pattern of isolation-by-distance. Studies of microsatellite DNA-based population genetic patterns in invasive D. rostriformis bugensis in other parts of the world have been limited to recently established populations and likewise show similar absences of strong genetic structuring.
The impacts of small impoundments on headwater streams have received little attention despite their potential to have local and broad-scale ecological impacts. These impoundments might alter stream hydrology, geomorphology, and facilitate the spread of invasive species. Given that prairie stream communities have adapted to highly variable conditions, they might resist disturbances associated with small impoundments. To test the resistance of aquatic communities to the disturbances associated with small impoundments, we surveyed intermittent headwater prairie streams in both unimpounded and impounded watersheds. We observed greater fish density and species richness in unimpounded watersheds and two species occupying a greater proportion of sites in unimpounded than impounded watersheds. In contrast to fish communities, we observed no difference in crayfish density or the community structure and biomass of aquatic insect and snail communities between unimpounded and impounded watersheds. Increased sensitivity to disturbances associated with small impoundments by fishes might be attributed to their limited dispersal capabilities.
Cross-cutting multidisciplinary evidence sufficiently demonstrates that wild, free-ranging bison (Bison bison) that occupy portions of the House Rock Valley and Grand Canyon North Rim in northern Arizona are native wildlife at the southwest edge of their historical range. Wildlife at the edge of historical range can play an important role in the conservation of species after declines in distribution and abundance. Very low density bison likely approximate long-term prehistoric and historic conditions on the southwestern Colorado Plateau. Small, low-density bison herds managed as free-ranging wildlife could approximate these historic conditions, coexist with sensitive landscape and cultural resources, and contribute to a bison metapopulation, thereby contributing to the continental conservation of this species.
In an effort to identify landscapes that provide honey bee (Apis mellifera L.) colonies with the most sustainable pollen sources, we conducted an extensive palynological analysis on trapped pollen collected from honey bee hives located in various agricultural landscapes. Collected pollen, honey bee preferences, and potential exposure to pesticides through collected crop pollen were investigated. We collected 128 trapped pollen samples throughout the 2015 season from 16 honey bee colonies distributed in four different agricultural landscapes: a high agricultural (High-AG) area, a moderate agricultural (Mod-AG) area, a low agricultural (Low-AG) area with high levels of urban activity, and a nonagricultural (Non-AG) area. We carried out comprehensive pesticide residue analyses on representative sets of pollen samples. Our results indicate that the Low-AG area with high levels of urban activity had significantly greater pollen diversity than other locations and had the least fluctuation in pollen types across the season. We recorded the lowest pollen diversity in both the High-AG and Non-AG areas with only 23 pollen types, suggesting that both settings lack a diversity of plant species attractive to honey bees. Noncrop pollen collected by honey bees largely exceeded the crop pollen in number and amount, indicating that bees' pollen-diet relies on a large spectrum of noncrop flowers. None of the pesticide residues identified in the pollen samples approached the honey bee 50% lethal dose concentrations.
We studied factors that affect the abundance of feces of the eastern cottontail (Sylvilagusfloridanus) in an ecological reserve in Mexico City. We measured the abundance of fecal pellets as an estimator of cottontail abundance, as well as different factors that may affect their abundance: predator presence, terrain ruggedness, soil depth, and plant cover. We found that predator presence was the most important factor reducing the abundance of cottontails, whereas terrain ruggedness was the second most important because the cottontail cannot climb effectively. Plants were less significant than expected but Manfreda scabra had a substantial positive effect on cottontail abundance.
We obtained 23 new records of nine-banded armadillos (Dasypus novemcinctus) in the state of Sonora, Mexico, that extend their known distribution range. Nine-banded armadillos are not well known in Sonora, where their habitat encompasses vegetation types that include tropical thornscrub, a transitional biome between Sonoran desertscrub and tropical deciduous forests, and oak woodland, excluding the Sonoran desertscrub. They occur from 50 to 1,656 m above sea level. Precipitation restricts their distribution to areas with a mean annual precipitation of ≥300 mm; otherwise, they occupy irrigation areas and riparian habitats. It is possible that the range of nine-banded armadillos is expanding in Sonora.
We tested the influence of grasshopper coloration on the foraging preferences of juvenile collared lizards (Crotaphytus collaris) that prey on grasshoppers. The study site harbored three grasshopper species with coloration that varied considerably: Melanoplus differentialis (yellow), Syrbula admirabilis (green), and Ageneotettix deorum (brown). The yellow M. differentialis were also heavier per unit body length than the other two species, which may decrease their net profitability if the additional mass indicates a thicker exoskeleton. We conducted prey-choice trials in the field that involved the simultaneous presentation of three tethered S. admirabilis (green) grasshoppers matched for total length, but we painted each grasshopper differently to mimic the green, brown, or yellow coloration of each prey species. Coloration influenced foraging choice by lizards, with fewer attacks on prey painted yellow to mimic M. differentialis, despite their relatively larger biomass. Results suggest that foraging choices based upon prey color, which may influence net profitability, merit further experimentation in collared lizards.
We evaluated the concentrations of three heavy metals (cadmium, chromium, lead) in eggs and caudal scutes of nesting female Crocodylus moreletii in El Carpintero Lagoon, Tamaulipas, Mexico, in the months of May to August 2013. Samples were processed and analyzed based on the method of flame atomic absorption spectrophotometry at the Centro de Investigación and Tecnología en Saneamiento Ambiental (CITSA). Our results showed the presence of cadmium, chromium, and lead in both caudal scutes and eggs. The three heavy metals showed values in nesting females of 20.3, 5.0, and 28.0 mg kg-1, respectively. We observed significant differences in levels of cadmium and lead among nests but not with levels of chromium. The variations in heavy metal concentrations in eggs suggest that extrinsic and intrinsic factors simultaneously affect crocodiles during the reproductive season. Our levels were high compared with other species of crocodilians and are above thresholds established by Mexican pollution laws.
We collected the skeleton of a big free-tailed bat (Nyctinomops macrotis) at a wind energy facility in Starr County, Texas. This is the first specimen record from the Lower Rio Grande Valley in southern Texas.
Caddisflies in the genus Phylloicus are often considered to be dominant shredders, or consumers of terrestrial leaf litter, in tropical and subtropical streams. However, few studies of their diet have been conducted in the field. In this article we report observational and stable isotope data demonstrating that Phylloicus mexicanus larvae also consume animal detritus in Ramsey Canyon, a montane headwater stream in southeastern Arizona. These data support the hypothesis that Phylloicus rely on animal material to meet nutritional demands and should be considered generalist detritivores rather than obligate consumers of leaf litter. Our work also suggests that the drought-driven loss of predatory Hemipterans, which leave behind animal carcasses after feeding, could exacerbate the effects of stream drying on Phylloicus populations.
In Mexico, the ferruginous pygmy-owl (Glaucidium brasilianum) is widely distributed and is considered a generalist predator consuming insects, mammals, reptiles, and amphibians. In this note we report the first evidence of a ferruginous pygmy-owl consuming an entire iguana (Iguana iguana) in the state of Veracruz, Mexico, on 7 July 2012 near Rio Jamapa, and include feeding behavior. Although the ferruginous pygmy-owl has been known to feed on reptiles, this is the first documented case of this owl feeding on this species of lizard. This event permits us to increase the knowledge about the diet of this predator and provides the way in which the pygmy-owl consumes prey items.
We present new information on 12 species of birds from the state of Hidalgo, Mexico. Five species are considered new to the state of Hidalgo: fulvous whistling-duck (Dendrocygna bicolor), mottled duck (Anas fulvigula), Clark's grebe (Aechmophorus clarkii), magnificent frigatebird (Fregata magnificens), and yellow-headed parrot (Amazona oratrix). Prior to this study, these species were unknown in the state of Hidalgo. In addition, we present new information on seven species previously recorded from the state of Hidalgo: Virginia rail (Rallus limicola), russet-naped wood-rail (Aramides albiventris), upland sandpiper (Bartramia longicauda), scissor-tailed flycatcher (Tyrannus forficatus), Cassin's sparrow (Peucaea cassinii), Brewer's sparrow (Spizella breweri), and white-crowned sparrow (Zonotrichia leucophrys). Researchers have not recorded the upland sandpiper (B. longicauda) in Hidalgo in more than 100 years. Other species, such as the Virginia rail (R. limicola), and the russet-naped wood-rail (A. albiventris), have only received ambiguous references in the literature.
We documented between-winter site fidelity of orange-crowned warblers (Oreothlypis celata) in the Lower Rio Grande Valley of Texas, between 2004 and 2017. Overall, we recaptured 13.9% of the 201 banded birds in ≥1 subsequent winter season: 20.8% of the 101 birds banded in urban natural areas, and 7.0% of the 100 banded in rural areas. We recaptured 8 birds ≥3 winters after their initial capture, indicating extended winter site fidelity.