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Bergmann's rule predicts an inverse relationship between body size and environmental temperature in endotherms. The larger the organism, the lower the rate of heat loss by radiation; thus, larger organisms should be more likely to survive in colder places. This relationship is less clear in ectotherms. We tested Bergmann's hypothesis for a sample of 260 individuals of Anolis nebulosus from four Mexican populations ranging from a continental island to a forest at 2,100 m in elevation. Using analysis of variance, we tested for differences in body size (first principal component extracted from seven morphometric variables) among populations. Average body size was expected to be significantly larger in higher localities. Results did not conform to expectation; the island population was significantly larger in body size than the rest likely because of lower predation pressure. Also, we examined the relationship between body size, perch temperature (PT), and the difference between body temperature and PT. There were significant differences among populations in the range of PTs used. Individuals from highlands, where temperatures are colder and vary greatly, used a broader range of PTs and used perches that were colder than their body temperature. Only the largest individuals, mostly males, were able to use the coldest perches. In contrast, at lower sites, which had less thermal variation, lizards showed less variance in PTs, and there was no relationship between PT and size. In general, variation in PT and body size was smaller for females than for males. Results suggest a combination of heliothermy and heat conservation by size as regulatory strategies, and a trade-off between mating strategies and heat loss. For these populations, body size is one of a number of factors involved in temperature regulation; the particular combination of these factors on a population is probably a response to local environmental conditions.
For decades there has been confusion and uncertainty on how to clearly identify the two distinct species, Pinus strobiformis Engelm. and Pinus ayacahuite Ehrenberg. Pinus ayacahuite is further defined as two varieties, var. ayacahuite and var. veitchii. These species are of ecological importance throughout much of Mexico because they offer valuable ecosystem services. The objective in this work was to examine the morphological characteristics of cones and seeds from parent trees from six sites in northern Mexico and three sites in southern Mexico. The results show that the mean seed width and length per tree, mean cone weight per tree, and the 100-seed weight per tree were the best variables to accurately separate P. strobiformis from P. ayacahuite. Using these criteria, we found that P. ayacahuite var. veitchii is more similar to P. strobiformis than to P. ayacahuite var. ayacahuite.
Three species of robber flies (Asilidae) are recorded as preying on workers of Pogonomyrmex harvester ants in eastern New Mexico and western Texas: Cerotainiops abdominalis, Saropogon combustus, and Saropogon pritchardi. Of 379 prey records for C. abdominalis, 66% were Pogonomyrmex workers. Two species of Saropogon were collected in association with a large number of harvester ant workers: S. combustus (40% of 263 prey records) and S. pritchardi (94% of 288 prey records). All three species show a statistical preference for Hymenoptera, specifically for harvester ant workers, and avoidance of Diptera, Hemiptera, Lepidoptera, and Orthoptera prey. A brief review of invertebrate predators of Pogonomyrmex workers is given, with emphasis on asilid predators. For the three asilid predators mentioned in the article, seasonality, observed behaviors, and a list of known prey taxa are included.
The cloud forests comprise high levels of species richness and endemism, and are the most threatened habitat in Mexico. They are listed as priority regions for conservation nationwide. Here, we estimated species richness and relative abundance of birds and mammals using camera-traps in a cloud forest located in a biodiversity hotspot of Mexico. From December 2013 to December 2014, we sampled 538 independent records from 27 species, including 11 species listed with some level of threat. Expected species richness, using first-order Jackknife estimator, was 37.08 species DE ± 2.86. We reported the greatest number of birds and mammals observed in cloud forests using camera-traps, and a high relative abundance index for some species. We found a significant difference between species composition observed in our study and other studies using camera-traps in Mexico. We observed a similar species composition in a nearby tropical rainforest habitat, suggesting that the recorded species are not restricted to cloud forests and move between different habitats. This highlights the importance of this region as a connector with “Los Chimalapas,” the largest and northernmost rain forest patch in Mexico.
The Sprague's pipit (Anthus spragueii) is a passerine of North American prairies, breeding in the northern United States and southern Canada, and overwintering in the grasslands and deserts of the southern United States and northern Mexico. In recent decades, pipit populations have declined in both breeding and wintering ranges because of degradation and loss of native prairie. Previous research on this species has focused primarily on its breeding habitat and provided limited information on its wintering habitat. To help fill in these data gaps, we assessed wintering density along the Texas Gulf Coast Plain, as well as characteristics of the associated habitat. We used a distance-based line-transect sampling technique to estimate pipit densities during the winters of 2013–2014 and 2014–2015 at seven conservation sites and found Sprague's pipits at all sites. The highest number of detections and the highest density estimates were at the Attwater Prairie Chicken National Wildlife Refuge. Habitat associated with pipits included open grasslands with mixed forbs and low vertical cover. Although wildlife biologists consider pipits to be native grassland specialists in their breeding range, our analyses did not identify proportion of native grasses as an important variable. Instead, the physical structure of the vegetation (short and sparse grass cover) was most important to pipit presence. Our results suggest that habitat management to benefit wintering populations of this species should focus on vegetation structure, though native grassland cover might be important at a larger scale.
Steep-walled catchments are a source of wildlife mortality. Incidental to searching for carcasses under five wind turbines in the panhandle of Texas, we discovered vertebrate carcasses on a frequent basis in concrete oil-catchment basins associated with each turbine's transformer. During 2015 and 2016, we found remains of 62 vertebrates trapped in these basins. We recommend new designs that prevent entrapment and addition of escape ramps to existing basins to reduce the frequency of trapped animals. Mitigation of mortality of the level that we observed could significantly reduce this unnecessary impact on wildlife from what is a far-reaching and growing industry.
We conducted a study to determine whether the nonnative axis deer (Axis axis) exhibited behaviors that could be negatively impacting ponds and pools in ephemeral channels. To assess behaviors, we collected game camera-trap images at two sites within the Texas Hill Country with naturally occurring standing water sources frequented by A. axis. We analyzed images of A. axis for behaviors including wallowing, territorial marking, and drinking. We also analyzed water samples for turbidity and Escherichia coli, in order to determine potential impacts of axis deer on water quality. During this study, we observed only drinking behaviors by A. axis. Water quality parameters did not significantly correlate with A. axis visitation rates. The observations suggest limited impact of A. axis on water sources, contributing to a greater understanding of A. axis behaviors and potential impacts within the Texas Hill Country.
Blood-squirting from ocular sinuses is a unique defensive behavior widespread in horned lizards. During an ecological study in the state of Mexico, Mexico, we captured 24 males and 23 females of Phrynosoma orbiculare, of which three males squirted blood during gentle handling. Two individuals were of juvenile size, suggesting, with data from large adults, that P. orbiculare defensive strategy may be employed throughout life.
Wildlife biologists believe the red wolf (Canis rufus) is limited in the wild to the Red Wolf Recovery Experimental Population Area on the Albemarle Peninsula, North Carolina. Several black-and-white photos from trail cameras placed on the Environmental Studies Area of East Texas Baptist University in Marshall, Texas, indicate the presence of a large canid possessing wolf-like characters. Two pictures, in particular, indicate the wolf-like characters with estimated morphometrics at the upper range reported for body length, shoulder height, width of head, and width of nose pad. Hair samples and tracks from this location indicate the presence of Canis rufus in east Texas.
The Cajun dwarf crayfish (Cambarellus shufeldtii) is among the most broadly ranging dwarf crayfish species in North America. Little is known about the species' reproductive cycle in east Texas populations, and even less is known about the relationship between female body size and reproductive traits. This study seeks to characterize some reproductive traits of female C. shufeldtii as they correlate to body size. We recorded measurements of 23 berried specimens collected from an east Texas freshwater marsh, and established a positive correlation between female carapace length and number of eggs, as well as female total length and number of juveniles. Females were larger and had larger clutches than those reported from Louisiana. We also present some laboratory evidence for females reproducing multiple times in a single reproductive season.
We report the sighting of a mangrove cuckoo (Coccyzus minor) in June 2019 at Parque Bicentenario, Mexico City, Mexico. This record from the Trans-Mexican Volcanic Belt (TMVB) is 182 km from the closest published record within the TMVB, and 217 km away from its known distribution range in the Atlantic Slope and 475 km from the Pacific Slope. This sighting, and several recent sightings during the breeding season, might indicate dispersal into a new biogeographic province from its predominantly lowland range. Within this biogeographic province, this finding helps to better understand its distribution and habitat use in Mexico.
In this study we focus on the pollen morphology of Physaria kingii subsp. kaibabensis and two congeners, Physaria arizonica and P. kingii subsp. latifolia, found on the Kaibab Plateau, Arizona, to differentiate further among these species. We collected plant material from 2 sites/species, with 10 plants/site used to image 10 pollen grains/plant. We described pollen grains (i.e., polar axis [P], equatorial diameter [E], P/E ratio, shape, exine structure, and aperture number) using scanning electron microscopy. All species imaged had pollen grains with reticulate surfaces and were pentacolpate. We found significant differences among species for equatorial diameter and P/E ratio, but not for polar axis. This study provides additional information that can be incorporated in species descriptions.