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Geographic distribution among members of the Sigmodon hispidus complex (Sigmodon hirsutus, S. hispidus, and S. toltecus) were examined using DNA sequences from the mitochondrial cytochrome-b gene. Geographic distribution of each taxon was defined based on DNA sequences obtained from 69 samples (19 newly obtained and 50 from previous studies) collected from North, Central, and South America. These data indicated that S. hispidus is restricted to the southern one-half of the United States and northeastern Mexico (Nuevo León and Tamaulipas), S. toltecus occupies the eastern one-third of Mexico (central Tamaulipas) to northern Honduras, and S. hirsutus is distributed from central Chiapas and southeastern Oaxaca to northern South America (Venezuela). The newly collected data extend distributions of S. hispidus from the southern United States southward into northeastern Mexico and that of S. toltecus from Chiapas, Mexico, southward to Honduras. Genetic divergence and patterns of phylogeography were examined within each taxon.
We investigated associations between rainfall and body condition of desert mule deer (Odocoileus hemionus eremicus) in the Sonoran Desert, California, using two indices of condition based on body fat: a categorical score based on subcutaneous fat and visibility of bones under the skin of free-ranging animals via remote photography, and percent fat in the marrow of long-bones of harvested males. There were positive correlations between rainfall and proportion of deer in good condition (r = 0.60, P = 0.064) and proportion of deer in fair condition (r = 0.70, P = 0.017). Proportion of deer in poor condition was negatively correlated with rainfall (r = −0.72, P = 0.020). There was evidence of a year effect on percent fat in the marrow of metacarpus and metatarsus bones (P = 0.030), such that years in which deer had lower average marrow fat coincided with years having lower rainfall. These findings demonstrate the importance of rainfall, likely operating through quantity or quality of forage, on body condition of mule deer, which have subsequent effects on demography. An understanding of these patterns will continue to be important for the conservation of ungulate populations in arid regions.
Recruitment of pronghorns (Antilocapra americana; fawns∶100 females) through late summer was positively correlated with precipitation during the previous winter (October–April) on 10 areas in Arizona during 1983–2002. There was no evidence of serial autocorrelation in recruitment of fawns and no strong within-year effects, even after accounting for differences in winter precipitation among sites. There was no evidence that the relationship between winter precipitation and recruitment differed among populations. Winter precipitation explained 38.5% of variability in recruitment among years within populations. We hypothesize that winter precipitation is a limiting factor affecting recruitment in populations of pronghorns in arid and semi-arid habitats in Arizona.
Ash Meadows National Wildlife Refuge, Nye Co., Nevada, is a small oasis in the northern Mojave Desert. Changes in use of land through irrigated agriculture and associated pumping of groundwater, as well as mining peat moss, altered the environment prior to its designation as a refuge in 1984. We evaluated relationships between land use, land cover, and groundwater in Ash Meadows National Wildlife Refuge from 1948 to 2004. Recovery of land cover was documented following cessation of agricultural activities and pumping of groundwater. Land-use activities from 1948 to 1980 reduced land cover by 1,141 ha, while later changes in land-use activities allowed recovery of 935 ha of land cover. Limited change in groundwater might have aided in recovery of land cover, although no relationship was established between depth-to-groundwater and land cover.
This study was conducted to characterize fishery resources inhabiting salt-evaporation ponds and sloughs in South San Francisco Bay, and to identify key environmental variables that influence distribution of fishes. The ponds, which were originally constructed and operated for commercial production of salt, have undergone preliminary modifications (installation of culverts, gates, and other water-control structures) in preparation for full restoration to mostly tidal wetlands over the next 2 decades. We sampled fish from two salt-pond complexes (Alviso complex and Eden Landing complex), each consisting of several pond systems and their associated sloughs. Cluster analysis of species of fish indicated that at least two species assemblages were present, one characteristic of ponds and the other characteristic of sloughs and slough-like ponds. The slough-like ponds exhibited water-quality conditions (especially salinity) that resembled conditions found in the sloughs. Pond fishes were represented by 12 species, whereas slough fishes were represented by 22 species. Except for bay pipefish (Syngnathus leptorhynchus), which was unique to ponds, all species present in ponds also were in sloughs and slough-like ponds. These results indicated that species of fish in ponds originated from the sloughs. According to canonical-discriminant analysis, four environmental variables were useful for discriminating between the two species assemblages. Most discriminatory power was contributed by the index of habitat connectivity, a measure of minimum distance that a fish must travel to reach a particular pond from the nearest slough. Apparently, as fish from sloughs enter and move through interconnected salt ponds, environmental stress factors increase in severity until only the more tolerant species remain. The most likely source of stress is salinity, because this variable was second in importance to the index of habitat connectivity in discriminating between the two species assemblages. Water temperature and concentration of dissolved oxygen also seemingly influenced spatial distribution of fishes, although they were less important than salinity.
We studied assemblages of small mammals in four types of coniferous forest (white fir, red fir, mixed-fir, and pine-cedar) in the Sierra Nevada of California for 2 field seasons (2003–2004). We assessed production of cones by dominant species of conifers in both years. Production of cones was greater overall in autumn 2003, but varied within type of forest and between species of conifers. Parallel to this, mean maximum densities of North American deermice (Peromyscus maniculatus) increased in 2004 (from 0.7–7.3 individuals/ha to 65.7–112.7 individuals/ha). Size of populations of golden-mantled ground squirrels (Spermophilus lateralis) were similar in both years; typical of hibernating species, this taxon occurred at low densities in May (6.6 ± 0.2), peak densities were in September (24.5–32.5 individuals/ha), and their populations declined in October (9.2 ± 4.8). Long-eared chipmunks (Tamias quadrimaculatus) reached higher densities in red fir (48.2 ± 13.4 individuals/ha) and mixed-fir forests (36.0 ± 13.5 individuals/ha) than in white fir forests (7.6 ± 2.7 individuals/ha), and all populations peaked in September. Shadow chipmunks (Tamias senex) remained at lower densities than T. quadrimaculatus except during September 2004, when they reached high densities (54.6 ± 26.8 individuals/ha). Survival of P. maniculatus was dependant on an interaction between type of forest and month, with additive effects of over-winter survival and mean production of cones in autumn 2003. Survival of S. lateralis varied by month, whereas survival in both species of Tamias varied with the interaction of type of forest and month, plus additional effects of over-winter survival and mean production of cones for T. quadrimaculatus. Dusky-footed woodrats (Neotoma fuscipes) were present at lower elevations and reached greatest densities in pine-cedar forests. Northern flying squirrels (Glaucomys sabrinus) were not captured commonly, and they occurred predominantly in red fir forests.
We investigated effects of prescribed understory fire and shrub density on the pinyon deermouse (Peromyscus truei), brush deermouse (P. boylii), and California pocket mouse (Chaetodipus californicus) in a mixed blue oak-coast live oak (Quercus douglasii-Q. agrifolia) woodland of coastal-central California. We simultaneously estimated survival and abundance of all species during pre-burn and post-burn. Abundance of pinyon deermice and California pocket mice was significantly higher in plots with high (>25%) shrub cover compared to plots with low (<10%) shrub cover. A light-to-moderate intensity, prescribed, understory fire had no significant effect on survival for any of the three species we investigated. The fire significantly reduced abundance of pinyon deermice in the trapping session immediately after the fire, but abundance increased in subsequent trapping sessions relative to controls. Low intensity, prescribed, understory fire in oak woodland is unlikely to significantly alter populations of rodents if patches of well-structured habitat are maintained. Benefits of prescribed fire for oak woodlands in reduction of the risk of wildfire and rejuvenation of vegetation likely outweigh any short-term negative effects on populations of mice.
Toxins of Xenopus laevis elicit gaping responses in some snakes, but introduced populations of this species in California provide an additional food source for Thamnophis hammondii with no observable ill effects to the snake. This study addresses the locomotor performance of T. hammondii after consuming this toxic frog. Endurance and speed of T. hammondii were measured along a 2-m long racetrack when subjects were not fed recently, when they were fed sunfish (Lepomis, a non-toxic prey), and when they were fed X. laevis. Snakes tended to be slower after eating, but ingestion of X. laevis did not affect either measure of locomotor performance in T. hammondii. Because performance of T. hammondii is not compromised, selective pressure against consumption of X. laevis probably is absent.
We use multiple years of collections in rivers, perennial wetlands, and ephemeral tinajas to report on overall biodiversity of aquatic invertebrates in the Grand Staircase–Escalante National Monument, Utah. A total of 570 samples of aquatic invertebrates was collected at 166 locations. Over the study period, invertebrates were identified from 31 orders, 104 families, and 192 genera. Major habitat types (rivers, perennial wetlands, and ephemeral tinajas) supported unique and taxonomically rich assemblages of invertebrates; taxonomic richness was greatest in rivers. Among rivers, richness of genera of aquatic invertebrates was greatest in groundwater-fed streams and perennial, snowmelt-runoff, rivers and least in flood-prone rivers. Future studies should focus on identifying and collecting invertebrates from unique habitats, especially the numerous wetland-like habitats that occur across the Grand Staircase–Escalante National Monument, such as hanging gardens and alcove pools, as well as ephemeral streams.
Emus (Dromaius novaehollandiae) have been commercially farmed in the United States since the early 1980s, but the market for emu products has never been large. Emus have escaped captivity and have been surviving and successfully reproducing in the wild. To determine if there was potential for competition with native species of wildlife, we examined diets of free-ranging emus in the Cross-Timbers and Prairies eco-region of Texas during 1999 and 2000. Diets of emus were composed of native grasses, forbs, mast, drupes, and leaves. In addition to native foods, emus also were consuming large quantities of livestock feed and agricultural crops. Free-ranging emus have potential to compete with native species of wildlife, particularly birds, if their numbers continue to increase.
The Sonoran pronghorn (Antilocapra americana sonoriensis) has been listed as endangered since 1967, yet little is known about its behavior due to difficulties observing them in the wild. During a study of Sonoran pronghorn in a semi-captive breeding facility in southern Arizona, we observed behaviors and timing of life-history events that have not been documented in peer-reviewed literature, including birth dates of fawns, pre-parturient and post-parturient behavior, timing of breeding season, behavior during the breeding season, date of horn casting by males, and response to predators. Behavior of the Sonoran pronghorn before and after parturition, during breeding, and toward predators was consistent with that reported for other subspecies. Timing of breeding, parturition, and horn casting all occurred earlier than reported for more northerly populations. Variation in timing of life-history activities was the main difference between the Sonoran pronghorn and other subspecies and would be expected due to the correspondence between seasonal rainfall and forage conditions in the Sonoran Desert and timing of parturition.
Soil was collected in 2002–2003 from a cienega in southeastern Arizona to assess species present as seeds in the soil seedbank. In 2002, dominant vegetation was bulrush (Schoenoplectus pungens). Due to drought-related drying of the marsh and other hydrological changes, vegetation at the study site subsequently shifted to a monoculture of upland sunflower (Helianthus annuus). In greenhouse experiments, a total of 20 species germinated from the seedbank soil. The most abundant germinants were bulrush, cattail (Typha domingensis), and spikerush (Eleocharis macrostachya). The endangered Huachuca water umbel (Lilaeopsis schaffneriana ssp. recurva) germinated in several of the samples and additional seeds were present in the soil. A decline in total density of seeds occurred over the course of the study, probably due to loss of wetland species. Species composition of the seedbank and standing vegetation were not correlated, which is a common result in studies of seedbanks. If hydrology is restored, we predict many of the wetland species will germinate and recolonize the area, although this is limited by duration of seed viability. Thus, management of the wetland should include examination of current hydrology as soon as possible if natural reestablishment of wetland species, particularly Huachuca water umbel, is desired.
We document how two species of desert aquatic insects use positive rheotaxis to escape drought in desert rivers. We observed ca. 3,600 adults of the long-toed water beetle Postelichus immsi (Coleoptera: Dryopidae) crawling upstream concurrent with upstream recession of surface water in the Santa Maria River, La Paz and Mohave counties, Arizona. At the same time, we observed larvae of the gray sanddragon Progomphus borealis (Odonata: Gomphidae) burrowing and swimming upstream in large densities (690 larvae/m2). Both taxa moved with sufficient speed to arrive at perennial reaches of the river before being overtaken by drought.
Recent phylogenetic work has demonstrated that the ability of species of the angiosperm family Nyctaginaceae to self-fertilize is evolutionarily labile. However, the potential for further investigation of the evolution of mating systems in the family is limited, because there is no information on reproductive biology for several genera. I performed an experiment on a natural population of Tripterocalyx carneus to determine whether this species is self-compatible. Individual flowers were emasculated, bagged to exclude pollinators, or both. Flowers that were bagged but not emasculated set viable fruit in the majority of cases, which demonstrates that this species is self-compatible.
Extensive surveys of recent occurrences of Pseudemys gorzugi and its likely historical distribution in the Rio Grande Basin reveal a low population density and a paucity of juveniles. Genetic analyses of the mitochondrial ND4 gene and five microsatellite DNA markers indicate the population may be relatively homogeneous throughout its range. In addition, research shows evidence of multiple threats common to chelonian populations, including habitat degradation, introduction of fire ants, and commercial collection for the pet trade. This research provides state management authorities with essential data to determine if additional conservation efforts are necessary to protect this unique species.
We report the cladoceran Diaphanosoma fluviatile Hansen 1899 in Lake Waco and Lake Mexia, two reservoirs located in central Texas. This species is formerly known from Central and South America and only recently was reported from some locations in Louisiana and Florida, and from the state of Veracruz, Mexico. Our new records represent a westward expansion of records previously documented in the southern United States.
This report is the first to document giant anteaters (Myrmecophaga tridactyla) in Nicaragua. An indigenous hunter killed four giant anteaters in the Bosawas Biosphere Reserve, Nicaragua. The Mayangna and Miskito residents of the reserve do not eat giant anteaters, but hunters sometimes kill the animals because of the threat they pose to hunting dogs.