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Abronia macrocarpa is endemic to Texas and it is listed as endangered by federal and state agencies, but it is believed to have a high potential for recovery. Reintroduction is a potential option for recovery of this species and this could be accomplished using seeds planted in the field or transplanting individuals produced ex situ from seeds. We used a split-plot design to determine the percentage of seeds germinating in the field and to test effects of planting seeds in spring versus autumn. Season of planting significantly influenced percentage of germination. Seeds planted in spring (April 2005) exhibited 27.8% germination, while germination of seeds planted in autumn (November 2005) was only 0.8%. We also investigated the induction of seed germination in the laboratory. Difference in germination was 0–68.6% between the control and treatments. Combining scarification then warm stratification followed by cold stratification resulted in significantly higher germination than other treatments.
Although most cacti that have been studied are long lived, following individually marked plants in Boulder County, Colorado, for >7 years, we determined that average life span of Opuntia macrorhiza, the western prickly pear, is 3 years. A few individuals probably live >10 years. Vegetative reproduction, produced by rooting of cladodes, exceeded reproduction by germination and establishment from seeds. Both types of new recruits, from vegetative reproduction and seeds, had higher death rates than established plants. Size and frequency of flowering increased with age, although size both increased and decreased, sometimes dramatically, between years. Flowering correlated more strongly with size than with age. Estimates of population growth indicated these populations were stable (λ = 1.02). Elasticities suggest that the population was most sensitive to survival of smaller plants.
Abundance of seedlings of functional groups (woody plants, grasses, and forbs) was measured monthly for 2 years under 10 replicates of three nurse plants (Caesalpinia mexicana, Cordia boissieri, and Ebenopsis ebano) at 90, 350, 540, and 670 m above sea level in northeastern Mexico. Across elevations, there were more forbs than grasses and more grasses than woody plants. Grasses and forbs were denser in spring, summer, and autumn than in winter; greatest abundance of seedlings from woody plants occurred during summer and autumn. Abundance of seedlings across elevations was greater under E. ebano and C. boissieri than under C. mexicana. For all species and for functional groups separately, abundance of seedlings was greater at higher elevations than at lower elevations.
We determined that Eupatorium petiolare was either wind pollinated or self-fertilized, that Tagetes lunulata and Verbesina virgata showed autonomous self-fertilization, that Dahlia coccinea seems to be self-incompatible and pollinated by diurnal insects, and that, although overall longevity of capitula of V. virgata was greater in shaded sites, production of fruit per capitulum was greater in sunny sites. Overall longevity of capitula and longevity of capitula in the mature-flower stage showed great variability among species; overall longevity of capitula was longer for those species flowering during the rainy season and longevity of the mature-flower phenophase was shorter for D. coccinea (the only species dependent upon vectors for its pollination). High density of flowers, few barriers to dispersal of pollen (low arboreal coverage), and increased photosynthetic radiation typical of sunny sites seem to favor transfer of pollen, resulting in higher pollination and fruiting success than that experienced by plants in shaded sites.
We studied a population of Plethodon albagula inhabiting an abandoned mine in Garland County, Arkansas, to test whether variables such as fecundity, diameter of egg, total number of eggs produced, and total number of clutches were influenced by precipitation or prescribed burning. We also compared ratios of juveniles to adults during summer, a period when P. albagula sought refuge in the mine, to determine if prescribed burning influenced certain life stages more than others. Comparing years before and after burning and accounting for the influence of precipitation, we did not detect a significant effect of the prescribed burn on any reproductive variable. However, we did discover a decline in some reproductive variables 1.5 years post-burning. There also was no decline in the ratio of juveniles to adults before or after the burn. Prescribed burning in the inactive season did not affect reproduction or age composition of the population of P. albagula.
Parthenogenetic Aspidoscelis tesselata (pattern class C) reaches the northern limit of its distribution in Ninemile Valley, Otero County, Colorado. Its coexistence with gonochoristic A. sexlineata permitted comparison of diets between species of different sizes, reproductive modes, and evolutionary histories. Based on numbers of prey in stomachs, A. sexlineata had a broader diet than A. tesselata C in June and July; however, breadth of diets calculated from volumes of prey were nearly the same for the two species. Despite the larger size of A. tesselata C, dietary resources were not partitioned by size and foods present exclusively in one species were rare in its diet. Overlap of diets in June could be explained by chance, but this was not true for July. Remarkably high dietary overlap in July resulted from both species taking advantage of an annual surge in abundance of grasshoppers. There was no evidence that either species was affected adversely by presence of the other.
We investigated diet of cougars (Puma concolor) in the eastern Sierra Nevada, California, following a decline in the population of mule deer (Odocoileus hemionus). Mule deer declined 84% from 1985 to 1991, a period concurrent with declines in bighorn sheep (Ovis canadensis sierrae; an endangered taxon). An index to numbers of cougars lagged behind those declines, with a reduction of ca. 50% during 1992–1996. We determined diet of cougars by analysis of fecal samples collected during 1991–1995, when the population of mule deer was <25% of its former size. Mule deer was in 79% of 178 feces in winter and 58% of 74 feces in summer. Although most (69%) fecal samples in winter were <5 km from, or within (25%) winter range of bighorn sheep, none contained evidence of bighorn sheep. One fecal sample in summer contained remains of bighorn sheep, indicating that those ungulates were not an important component of the diet during our investigation.
In ponderosa pine-Gambel oak (Pinus ponderosa-Quercus gambelii) forests of north-central Arizona, we examined occupancy and habitats of four species of sciurids (rock squirrel Spermophilus variegatus, golden-mantled ground squirrel S. lateralis, gray-collared chipmunk Tamias cinereicollis, cliff chipmunk T. dorsalis). Numbers of captures were highly variable, suggesting a patchy distribution of species. All four species co-occurred on only one of the study sites. Gray-collared chipmunks and golden-mantled ground squirrels were relatively common on one site only. Golden-mantled ground squirrels were associated with mature forests with high canopy cover and low basal area, whereas gray-collared chipmunks were in locations with large numbers of logs and shallow litter. The two species of chipmunks appeared to be separated in space; gray-collared chipmunks were more common where cliff chipmunks were least common. Rock squirrels were relatively ubiquitous. There was evidence for an association of rock squirrels with increasing rocky cover and decreasing canopy cover, whereas cliff chipmunks occupied rocky areas with high canopy cover and numerous shrubs.
Using mist-netting and observational surveys in southeastern Arizona, we documented use of habitat by 12 species of birds that migrate to this Mexican monsoon region to molt. During the drier monsoon season in 2007, higher proportions of molt-migrants congregated at riparian areas. During the wetter monsoon season in 2008, a wider range of habitats was used. Molt-migrants generally selected habitats similar to those of their breeding territories; however, in some cases, species appeared to shift habitats for molt, in response to environmental effects. For example, high use of grasslands by molting Lucy's warblers (Oreothlypis luciae) in 2007 and by lazuli buntings (Passerina amoena) and lesser goldfinches (Carduelis psaltria) in 2008 suggests variable responses to relative strength of the monsoon season. Our results underscore the need to conserve native grasslands and riparian areas; habitats in which we detected molt-migrants most frequently. Our results also indicate the need to conserve a mosaic of habitats to account for adaptive selection in response to variable environmental conditions.
During 2005 and 2007, we examined status of populations of the American crocodile (Crocodylus acutus) in three rivers at El Cajon Reservoir in central Honduras. Number of crocodiles per kilometer of survey varied by river and time of study. Most observations were of hatchlings and yearlings, but juveniles, subadults, and adults also were observed. Sex ratio in the reservoir was 1∶1.4 male∶female. Assuming that sex ratio and size-class structure were representative of the overall population, our study suggests that the population in El Cajon Reservoir is stable.
Our objectives were to determine which habitat variables had the greatest influence on densities of the Three Forks springsnail (Pyrgulopsis trivialis) and pond snail (Physa gyrina), and to examine interactions between the two species. We measured density and several habitat variables in Three Forks Springs and Boneyard Bog Springs in east-central Arizona. Density of Three Forks springsnails was greatest (500/m2) in shallow water (<5.6 cm), where density of pond snails was less (<4.6/m2), and closer to the springhead (<0.8 m). Density of pond snails was greatest (66/m2) further away from the springhead (≥32 m) and when temperatures were greater (≥15.8°C). Density of pond snails was low (1.1/m2) closer to the springhead (<32 m) when pH was less (<8.4). The two snails apparently partition habitat in response to competition for food or presence of predators.
We examined whether chronic exposure of traps to disinfectant reduced trappability of rodents as compared to new traps. We tested whether rodents initially chose between treated (disinfected) and new traps and if total number of captures differed between these treatments. Disinfectant did not reduce catchability of traps; rodents actually preferred treated traps. In initial pair-wise choice tests, rodents overall and the predominant North American deermouse, Peromyscus maniculatus, chose significantly more treated than new traps, although this difference disappeared as time of exposure of new traps in the environment increased. Total captures of small mammals and North American deermice did not differ between treated and new traps. Therefore, treated traps were never avoided; this has important implications in general, but especially for long-term studies where censuses are conducted using pre-disinfectant and post-disinfectant protocols.
During 2003–2005, I surveyed 82 sites on the North and South rims of Grand Canyon, Coconino County, Arizona, to test effectiveness of four non-invasive techniques for detecting carnivores and to assess patterns of co-occurrence among pairs of species. Techniques were not equally effective for detecting carnivores. Searches of transects for feces, tracks, and other evidence yielded the greatest number of detections; remotely triggered cameras and track plates had the greatest probabilities of detecting common species and also produced detections of smaller and rarer carnivores; and hair traps generally were ineffective. Even after accounting for variation in probabilities of use of habitats by species due to characteristics of sites, two pairs of carnivores had limited co-occurrence. Coyotes (Canis latrans) and bobcats (Lynx rufus) did not co-occur at sites on the North Rim, and coyotes and gray foxes (Urocyon cinereoargenteus) co-occurred less than one-half as frequently as expected in the South Rim.
Small mammals were captured at Swan Lake National Wildlife Refuge, Chariton County, Missouri, using Sherman live traps and Museum Special kill traps in five habitats. Trapping generated 1,078 captures representing 10 species in 6,400 trap nights. Museum Specials captured significantly more small mammals than Sherman live traps. Both types of traps were equally likely to capture males and females and there was no difference in captures among habitats. Significantly more western harvest mice (Reithrodontomys megalotis) and house mice (Mus musculus) were captured in Museum Specials than in Sherman live traps. Museum Specials were sprung-but-empty significantly more often than Sherman live traps.
During two studies of mortality in fawns of desert mule deer (Odocoileus hemionus eremicus) in Crockett County, Texas, and Gila County, Arizona, we recorded rates of retention and problems with vaginal-implant transmitters (VITs). Our objectives were to determine if rates of retention differed between studies, years, timing of insertions, and width of wing of VITs. In Texas, VITs with wings 6.75-cm wide were shed successfully at parturition 73–77% of the time, whereas in Arizona, VITs were shed successfully 43% of the time. Additionally, in Arizona, VITs with 8.20-cm-wide wings were shed successfully 91% of the time. Our data suggested that optimal length of wings of VITs for mule deer may be dependent on locale. When designing a study using VITs, researchers should use the largest wing possible to ensure high rates of retention without physically harming deer.
We examined spatial extent of habitat that anaxyrids responded to in an arid environment. We used surveys of vocalizations and searches to identify toads after rainfall events to examine whether the spatial arrangement and proximity of earthen tanks could influence breeding populations of Anaxyrus cognatus and A. debilis. These species responded to the landscape complement of breeding sites inside a buffer of 5 km, a much larger distance than most studies have addressed.
We describe the migratory pattern of black terns (Chlidonias niger) in the Ojo de Liebre-Guerrero Negro coastal-lagoon complex and Guerrero Negro saltworks on the Pacific coast of Baja California Sur, Mexico. Most black terns (97% of total) were seen July–October, with 6,700 birds being the highest count per month (September). During spring, this species was observed only in April (220 individuals). We recorded 90% of black terns in the southeastern portion of Ojo de Liebre Lagoon, where they were in artificial (saltworks) and natural habitats (marsh and sandy shallows). In late summer (July–August), 94% were in the lagoon, by contrast, in autumn we recorded 96% in saltworks. Overall, black terns are a common transient in Guerrero Negro during summer and autumn and uncommon during spring. Black terns use these artificial and natural habitats as stopover areas during migration.
Pleistocene and Holocene fossils of the yellow-nosed cotton rat (Sigmodon ochrognathus) in New Mexico, Trans-Pecos Texas, and southern Chihuahua indicate past presence within the currently occupied geographic range, as well as occurrences at lower-elevation sites. Suggestions that post-Pleistocene colonization may account for occurrence of northern isolated populations cannot be falsified because extirpation followed by recolonization cannot be ruled out; however, current data indicate that such a scenario is unnecessary.
I tested effects of infection by the parasitic larval nematode Eustrongylides ignotus on reproduction in the livebearing western mosquitofish Gambusia affinis. Generally, parasitized females had fewer developing broods than nonparasitized females. Parasitic nematodes significantly reduced fecundity in the western mosquitofish.
The occurrence and distribution of Hemidactylus frenatus (common house gecko) in Mexico is known from dozens of miscellaneous notes, regional accounts, and unpublished records in museums that span >100 years. This information is gathered here, summarized, and mapped to document current distribution of the species in Mexico. A chronology of collections offers an indication of its dispersal there.
In 1995, we caught three Texas antelope squirrels (Ammospermophilus interpres) at two sites near Brackettville, Kinney County, Texas. One was captured in a habitat atypical for the species. This is the easternmost record and first record of the species in Kinney County.
To appraise conservation status of the Yaqui catfish Ictalurus pricei, we reviewed literature and unpublished records on a captive stock, examined voucher specimens at museums, re-sampled historical localities in the Yaqui, Mayo, and Fuerte river basins, and we surveyed rivers further south. A total of 72 specimens of native Ictalurus was collected in the Yaqui, Fuerte, Sinaloa, Culiacán, and San Lorenzo river basins. No native Ictalurus was collected in the Mayo Basin. Distribution of the Yaqui catfish appears restricted to the Yaqui, Mayo and Fuerte river basins, all of which now harbor nonnative blue (I. furcatus) and channel (I. punctatus) catfishes. The nonnative black bullhead (Ameiurus melas) is now known from the Yaqui Basin and the flathead catfish (Pylodictis olivaris) has been recorded anecdotally in the Yaqui Basin. Threats to the Yaqui catfish have increased in recent years and hybridization with the channel catfish now appears widespread. We conclude that the Yaqui catfish should be considered endangered throughout its range and that status of native populations of Ictalurus in the United States and Mexico should be reviewed and management intensified.
Stream flow modifications, such as reduced spring flow and construction of low-head dams, have led to declines in the headwater catfish (Ictalurus lupus) across much of its range, as has competition with channel catfish (I. punctatus). Hybridization between headwater catfish and channel catfish also poses a threat to the headwater catfish. Our analyses of cytochrome-b sequences of headwater catfish from the Frio River, Devils River, and Independence Creek indicated that a population of headwater catfish occurs in the Frio River of the Nueces Drainage, where it was considered extirpated since 1967, and that hybridization is occurring in populations that inhabit the Frio River and Independence Creek. No obvious sign of hybridization was present in the population of headwater catfish in the Devils River.