Showing papers in "Western North American Naturalist in 2002"

A heterotrophic desert stream? The role of sediment stability

Abstract: In autumn 1998 stream metabolism was measured in the Hassayampa River, Arizona, a Sonoran Desert stream, using single-station diel oxygen curves and an oxygen mass balance model. Oxygen consumption rates of parafluvial and channel sediments were determined with respiration chambers. Bedload of channel sediments (sand) prevented significant primary production by benthic autotrophs, despite favorable nutrient, light, and temperature conditions. Ecosystem respiration was relatively low (1.50 g O 2 m -2 d -1 ) and presumably fueled by production in the riparian zone and riverine marshes. Respiration rates in the parafluvial zone and in channel sediments ranged from 0.6 to 1.4 g O 2 m -3 sediment h -1 . Sediment organic matter (ash-free dry mass) was 4.0 ± 1.8 kg m -3 sediment and did not significantly differ between the channel and the parafluvial zone. Results indicate that heterotrophic processes may dominate the metabolism of desert stream segments over extended periods of time if unstable sandy bed sediments prevail.

Helminth parasites of seven anuran species from northwestern Mexico

Abstract: One hundred eighty-three specimens representing 7 anuran species were examined for helminth parasites: Bufo kelloggi, B. mazatlanensis, Leptodactylus melanonotus, Pachymedusa dacnicolor, Rana forreri, R. magnaocularis, Smilisca baudini . The following species were found: 8 species of Trematoda, Cephalogonimus americanus, Clinostomum attenuatum (larva), Glypthelmins poncedeleoni, G. quieta, Gorgoderina attenuata, Haematoloechus complexus, H. longiplexus , and Megalodiscus temperatus ; 2 species of Cestoda, Cylindrotaenia americana and Nematotaenia dispar ; 13 species of Nematoda, Aplectana incerta, A. itzocanensis, Cosmocerca podicipinus, Cosmocercella haberi, Cosmocercoides variabilis, Foleyellides striatus, Oswaldocruzia pipiens, Rhabdias americanus, R. ranae, Subulascaris falcaustriformis, Physaloptera sp. (larva), Physocephalus sp. (larva), and Spiroxys sp. (larva); and 1 species of Acanthocephala (cystacanth). Helminth species richness was 6.4 ± 2.4 s. Thirty-five new host records are reported.

Arbuscular mycorrhizae of mojave desert plants

Abstract: Roots of 15 Mojave Desert plant species were assessed for arbuscular mycorrhizal (AM) colonization in spring and autumn 1999. Another 19 species were assessed in autumn only. Perennial species were AM colonized, whereas annual species contained very low levels of AM hyphae or were nonmycorrhizal. The nonnative tree Tamarix ramosis- sima was also nonmycorrhizal. Levels of hyphae changed over the season in 2 species, arbuscle levels increased in 1 species, and vesicles decreased in 7 species. Mycorrhizal inoculum potential (MIP) was assessed in the soils associated with spring-collected plants. All soils were found to contain MIP. MIP values were not correlated with AM root colonization.

Improving seed germination of salicornia rubra (chenopodiaceae) under saline conditions using germination-regulating chemicals

Abstract: Salicornia rubra Neis. (Chenopodiaceae) is a salt-tolerant annual species occurring in salt playas of the Great Basin desert in western United States. It forms pioneer communities on the most saline location of an inland salt playa at Goshen, Utah. Seeds of Salicornia rubra are capable of germinating at 1000 mM NaCl at 25-35°C alternating temperature regime. Dormancy-regulating chemicals were evaluated for their ability to alleviate the innate and salinity- enforced dormancy in seeds of Salicornia rubra. Betaine, GA3, kinetin, fusicoccin, ethephon, thiourea, proline, and nitrate had no effect in alleviating primary dormancy. Increases in NaCl concentration progressively inhibited germina- tion of Salicornia rubra seeds. Ethephon, fusicoccin, GA3, kinetin, thiourea, and nitrate promoted germination under low saline conditions. At high salinity fusicoccin had no effect, whereas GA3, kinetin, and ethephon substantially allevi- ated salinity effects. Application of these dormancy-regulating compounds could be of practical value in seeding a saline area for restoration purposes, particularly under high saline conditions.

Diet and food-niche breadth of burrowing owls (athene cunicularia) in the imperial valley, california

Abstract: Burrowing Owls (Athene cunicularia) occupy intensively managed agricultural areas within the Imperial Valley of California, where they occur at high densities relative to other areas in the state, and yet reproductive rates are often low. Understanding diet and food-niche breadth may lead to insights into factors contributing to their poor repro- ductive performance. We tested the relative contribution of sex, year, and season on diet composition and food-niche breadth from analyses of stomach contents of adult Burrowing Owls (n = 53). Orthoptera dominated the diet; it accounted for 58.9% of the total number of prey items in all stomachs and was found in 98.2% of all samples. Rodents, a source of potentially limiting dietary calcium, were found in only 2 stomachs. We detected yearly and seasonal effects on estimated food-niche breadth. Mean food niche for the breeding season was broader (antilog of Shannon's index: 2.38 ± 0.15) and more even (Pielou's index: 0.67 ± 0.06) than for the nonbreeding season (1.83 ± 0.13, 0.49 ± 0.07, respectively) partially because of a greater frequency of Araneida, Isopoda, Lepidoptera, and Solpugida in the diet during the breed- ing season. Mean food-niche breadth for 1997 (2.25 ± 0.23) was broader than during 1994, 1995, and 1996 (2.07 ± 0.23, 1.98 ± 0.20, and 1.82 ± 0.40, respectively) because of a greater frequency of Araneida, Dermaptera, Isopoda, Lepi- doptera, and Solpugida. These results, and auxiliary diet information, suggest rodents were infrequent in the diet of Burrowing Owls in the Imperial Valley and may help explain their lower reproductive success relative to other areas of California.

Fertile island development around perennial shrubs across a Mojave Desert chronosequence

Abstract: —Spatial heterogeneity has been examined only recently as a factor in studies of ecosystem processes. The effect of this factor on desert organisms is exemplified in the “fertile island”—a concentration of essential soil nutrients under perennial shrubs. In this study we examined fertile island patterns in undisturbed desert areas and on abandoned roadways to see at what rate and magnitude these fertile patches reappeared after disturbance. Small-scale examination of patterns of soil P, organic matter, moisture, and bulk density showed that soils beneath Larrea tridentata (DC.) Cov. shrubs on the roads lacked the tight circular gradient in these variables that was characteristic of soils beneath control shrubs, even 88 years after road abandonment. The nature of the initial soil disturbance altered both spatial patterns of soil N and temporal patterns of fertile island development. Fertile island patterns for total soil N, available P, and organic matter were more circular than patterns for bulk density, texture, or pH. We suggest that patterns of soil heterogeneity may develop first for elements that may be limiting to desert shrub growth (N, P, organic matter), followed by spatial development in other less limiting soil factors (bulk density, texture, pH).

Ecological genetics and the translocation of native fishes: emerging experimental approaches

Abstract: Conservation biologists often use translocations to augment small populations, establish "refuge" popu- lations, or reestablish populations into historic habitat. For reasons that are poorly understood, translocations often fail. Further, translocations have both short- and long-term consequences for the evolutionary ecology of the targeted taxa. Unfortunately, most information on translocations has been derived from descriptive studies. Recent experimental approaches have provided new data to address a variety of topics associated with translocations, including inbreeding, outbreeding, the relationship between heterozygosity and fitness, and rapid evolution in populations established by translocation. We focus on genetic and ecological aspects of translocations but recognize that contributions from other fields will be essential for the long-term success of many translocation programs. Ongoing research regarding host-para- site interactions points out the need for extensive ecological data as well as genetic data to make informed decisions regarding translocations. Hypotheses derived from this field are ripe for rigorous experimental examination.

Do jaguars ( Panthera onca ) depend on large prey

Abstract: The jaguar ( Panthera onca ) has been classified as an opportunistic hunter that takes as many as 85 prey species, according to availability. In this study we analyzed jaguar food habits throughout its range to quantify the importance of small, medium, and large prey in the diet. Because peccaries ( Tayassu ) are present in most studies, we also tested their importance in relation to other prey items. We conclude that jaguars are equally using medium- and large-size prey, with a trend toward use of larger prey as distance increases from the equator. There was no significant difference between the importance of peccaries and other large prey.

Trichoptera and other macroinvertebrates in springs of the great basin: species composition, richness, and distribution

Abstract: Detailed surveys of aquatic invertebrates in 28 springs along the western border of the Great Basin were made using pan traps, emergence traps, black lights, and benthic sampling devices from 1994 to 1998. Although all macroinvertebrate groups were collected, caddisflies (Insecta: Trichoptera) were sampled most intensively. Fifty-eight species of caddisflies were collected from the 28 springs, with up to 18 species from a single spring. Although several springs had very similar physicochemical characteristics, none had identical trichopteran species composition. Using Ward's minimum variance clustering technique, and with all macroinvertebrates identified to the lowest possible level, we found 3 taxa assemblages. These assemblages occurred in springs with the following physical conditions: (1) warm water (15.9°C), low elevation (1794 m); (2) cold water (8.5°C), mid-elevation (2334 m); and (3) cold water (6.6°C), high elevation (1794 m). Although the warm water group had a distinct assemblage of invertebrates (amphipods, gastropods, Trichoptera), distinct assemblages did not separate the 2 cold water groups. Discriminant analysis indicated that tem- perature, conductivity, alkalinity, and elevation were most responsible for discriminating group 1 from groups 2 and 3; temperature and elevation distinguished the latter 2 groups. Spring permanence, lack of disturbance, and cold water temperatures were the factors most responsible for explaining higher species richness of Trichoptera.

Nest-Site Characteristics of Burrowing Owls ( Athene Cunicularia ) in the Snake River Birds of Prey National Conservation Area, Idaho, and Application to Artificial Burrow Installation

Abstract: Burrowing Owl (Athene cunicularia) populations are declining in many portions of their range, and research and management efforts into stemming declines are underway. One tool with promise is the artificial burrow, which can supplement nesting opportunities and play a role in research, mitigation, translocation, and reintroduction studies. However, few studies directly assess important burrow and surrounding topographic features upon which owls choose sites and then construct and install artificial burrows accordingly. In this study we (1) measure physical, vegeta- tive, and topographic characteristics of Burrowing Owl nest sites in the Snake River Birds of Prey National Conserva- tion Area (SRBPNCA); (2) compare used and unused burrows to determine features important in nest-site selection; and (3) use this information to help guide current and future construction and placement of artificial burrows in the SRBP- NCA. Owls nested in abandoned American badger (Taxidea taxus) burrows in areas with more than one burrow, close to roads and irrigated agricultural fields, and characterized by sparse and low vegetation dominated by nonnative plant species. Only one feature studied, tunnel entrance angle, corresponded with choice by owls; odds of burrow use decreased 17% with each 1° increase in slope of the tunnel entrance. Owls nesting near irrigated agricultural fields also had higher productivity. We discuss applications of our results to construction and placement of artificial burrows in the SRBPNCA and similar shrub-steppe environs in western North America.

Effect of soil microtopography on seed bank distribution in the shrub-steppe

Abstract: The relationship between soil surface cryptogamic crusts and seed banks was investigated in the shrubsteppe in the Lower Columbia Basin. Seventy-four percent of the seeds in a disturbed bunchgrass community were found in crevices bordering cryptogamic crust polygons. In a sagebrush/bunchgrass community, 89% of the seeds were found in crevices. In a disturbed bunchgrass community, Bromus tectorum seeds were found in both the seed bank and aboveground vegetation communities. Bromus tectorum seeds were located in the seed bank of a sagebrush/bunchgrass community, although it had a minor presence in the aboveground community. Seeds of Artemisia tridentata Nutt. were not found in either the bunchgrass or sagebrush/bunchgrass communities. The high number of seeds found in crevices bordering the cryptogamic crust suggests that crevices play a role in determining the small-scale distributional pattern of shrub-steppe plants at the Fitzner-Eberhardt Arid Lands Ecology Reserve.

Vegetation response to prescribed fire in Dinosaur National Monument

Abstract: —Much of western North America is dominated by dense, monotypic, late seral stands of big sagebrush (Artemisia tridentata Nutt.). These stands often have depauperate understories with limited species richness, diversity, and herbaceous cover. The National Park Service at Dinosaur National Monument, Colorado, is using both strategic and natural prescribed fire in Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle and Young) communities to foster intra-community (α-scale) and landscape diversity. This study analyzed an accumulated foliar cover data set between paired burn and control areas on 6 different sites during the last 20 years. Across the monitoring period, mean total vegetation cover of all combined sites was 44% control and 42% burn. Total vegetation cover in burn areas was higher than or equal to paired control areas within 2–3 years post-burn. Shrubs were essentially eliminated in burn areas, but perennial grass cover was 10–35% higher. Mean number of species on all sites and years combined was 17 control and 18 burn. Species richness was different on only 1 site-year, Dry Woman 1995 (P = 0.001, 15 control, 9 burn). Species similarity by site and between treatments ranged from 44% to 75%. Differences in Shannon-Weiner diversity index values between paired sites occurred in 6 of 20 years (P < 0.05). Index value differences on these 6 sites were due to a large annual grass component in burn areas. Prescribed burning successfully shifted late successional sagebrushdominated communities to earlier herbaceous-dominated successional stages without lowering total vegetation cover, while maintaining α-scale diversity and species richness.

Benthos recovery after an episodic sediment release into a Colorado Rocky Mountain river

Abstract: —During late September 1996, approximately 7000 m3 of clayto gravel-sized sediment was flushed from Halligan Reservoir, Larimer County, Colorado, into the North Fork Cache la Poudre River during dam inspections. Approximately 9.6 km of this river was partially or completely affected by this episodic sediment release. Pools up to 3.2 km downstream from the dam lost 50% of their volume. Hess samples taken from October 1996 to September 1997, 100 m downstream from the dam (site 1) and 3.2 km downstream (site 2), revealed effects of sediment on recovery patterns of benthic communities. A 2-way ANOVA was used to determine significant interactions using site and date as main factors. Pairwise differences were then compared using least squares means to determine significant dates within and between sites. Ten days after the sediment release, both density and taxa richness at site 1 (55 organisms per m2, 5 taxa) were significantly lower (P < 0.05) than site 2 (1156 organisms per m2, 25 taxa). These differences remained until June when species richness and densities increased. Plecoptera and Trichoptera colonized from June to September after being eliminated at site 1 and reduced at site 2. No permanently flowing tributaries exist within the study area; therefore, passive downstream drift from such inputs apparently did not influence recovery. Increased densities of taxa such as Baetidae, Hydroptilidae, Hydropsychidae, Chironomidae, Simuliidae, and Oligochaeta occurred plausibly by rapid reproduction. Based on pre-event data, community function completely changed at site 2 from a scraper community to one dominated by collector-gatherers.

Movements and home ranges of San Joaquin kit foxes ( Vulpes macrotis mutica ) relative to oil-field development

Abstract: We examined the effect of oil-field development on movements and patterns of spatial use of San Joaquin kit foxes ( Vulpes macrotis mutica ) on the Naval Petroleum Reserves in California (NPRC) in the San Joaquin Valley. To do this, we compared movements and home ranges of kit foxes from June 1984 to September 1985 in areas developed for petroleum production (30% of native habitat lost to production facilities) and areas with little development (3%). Distances traveled nightly by kit foxes did not differ between levels of petroleum development or between sexes ( P > 0.2). Mean length of nightly movements during breeding (14.6 km) was longer than during pup-rearing (10.7 km) and pup-dispersal (9.4 km) periods ( P = 0.01). Mean size of home ranges was 4.6 ± 0.4 ( s‾x ) km 2 ( n = 21) and did not differ between levels of petroleum development and sexes ( P > 0.2). Overlap of home ranges of foxes from the same social group (78 ± 4.3%) was greater than that of same-sex foxes (35 ± 7.8%) and males and females of different social groups (32 ± 8.0%, P P > 0.4). Despite extensive overlap of home ranges, kit foxes on NPRC maintained relatively exclusive core areas, particularly adjacent foxes of the same sex. Future studies should examine which levels of habitat conversion impact spatial use of kit foxes.

Temperature responses and habitat sharing in two sympatric species of Okanagana (Homoptera: Cicadoidea)

Abstract: —Okanagana striatipes and O. utahensis are species synchronous in location of activity and utilization of host plants. They possess similar acoustic behavior. Analysis of calling songs shows that calls overlap in frequency but differ in temporal pattern. Based on characteristics of the cicada auditory system and the species recognition mechanism, the potential for acoustic interference exists. Both species are ectothermic behavioral thermoregulators. Measurements of thermal preference and body temperature during singing show that although thermal preferences are similar, O. utahensis sings at a significantly higher body temperature. Differences in body temperature required to coordinate singing in the 2 species provide a partial temporal separation of acoustic signaling. We suggest the physiological mechanisms that permit synchronous utilization of a habitat by the 2 species are the production of calling songs of different temporal patterns and the presence of different thermal requirements, which may permit and/or facilitate temporal separation of the acoustic environment during the day.

Tree growth and regeneration response to climate and stream flow in a species-rich southwestern riparian forest

Abstract: We studied the influence of climate variables, stream flow, and topography on regeneration and growth of several riparian tree species (Acer negundo, Alnus oblongifolia, Fraxinus velutina, Juglans major, Platanus wrightii, Populus fremontii, Salix spp.) at an unregulated perennial stream, West Clear Creek, in central Arizona. A pulse of seedling regeneration occurred for Alnus, Fraxinus, Platanus, Populus, and Salix in 1995 and 1996 following high winter and spring surface flows in 1993 and high spring surface flow in 1995. In contrast, little regeneration occurred for Acer and Juglans under these conditions. Most seedlings occurred at the active channel topographic location, and few seedlings occurred at abandoned channel, gravel-boulder bar, and bench locations. Relationships between environmental variables and annual radial stem growth varied among species and between constrained and unconstrained reaches. High spring or winter surface flows were negatively related to growth of Acer, Alnus, and Platanus, whereas high spring surface flow was positively related to growth of Fraxinus. Positive relationships between precipitation and growth occurred only for Fraxinus and Juglans, suggesting greater use of surface soil water by these species. Annual radial growth was high for Platanus and Alnus, medium for Acer and Fraxinus, and low for Juglans. Overall, the tree species in our study responded individually, rather than collectively, in regeneration and growth to changes in stream flow and climatic variables.

Stoneflies (Plecoptera) of Mount Rainier National Park, Washington

Abstract: Mount Rainier National Park, with an area of 95,356 ha, is approximately one-third as large as the state of Rhode Island. The lowest point is 490 m in elevation in the southeastern corner near where the Ohanapecosh River crosses the southern boundary. Columbia Crest is the highest point at 4392 m. The entire park is a rugged landscape marked by the major topographical feature, Mount Rainier, comprising over 25,899 ha, almost one-third of the park. The park lies entirely west of the crest line of the Cascade Range. Most streams in the park originate on Mount Rainier; however, several large rivers meander through the park near its boundaries. One of the first attempts to summarize the stoneflies of Washington, including Mount Rainier National Park, was Hoppe's 1938 work that reported ca 8 species. Jewett (1959) reviewed the stoneflies of the Pacific Northwest and listed 7 species that had type localities in the park: Megaleuctra kincaidi Frison, Doddsia occidentalis (Banks), Soliperla fenderi ( Jewett), Frisonia picticeps (Hanson), Isoperla rainiera Jewett, Megarcys irregularis (Banks), and M. subtruncata (Hanson). Subsequently, Kathroperla takhoma Stark and Surdick (1987) was described from the park. Samples of adult stoneflies from 1994 to 2001 indicate the presence of at least 82 species, with 64% of these typical Pacific Northwest species, and 30 species, or 36%, widespread western North American species. Seventeen new Washington state records are listed, including a substantial range extension for Lednia tumana (Ricker). One undescribed species in the Sweltsa borealis complex was also discovered. We also present illustrations of male terminalia for Despaxia augusta (Banks) and Moselia infuscata (Claassen) to aid in the identification of these species.

Genetic Differentiation of Rare and Common Varieties of Eriogonum Shockleyi (Polygonaceae) in Idaho Using ISSR Variability

Abstract: Idaho populations of Eriogonum shockleyi are divided taxonomically into 2 varieties: E. shockleyi var. packardae, which is endemic to Idaho, and the typical variety, which is widespread in the western United States. Recent morphological investigations of E. shockleyi in Idaho have identified potentially reliable morphological characters for field identification of the subspecific taxa. This paper investigates the genetic basis for the separation of the 2 varieties of E. shockleyi using inter simple-sequence repeats (ISSR) markers. Although we found some morphological differences between the populations that correlated with the 2 varieties, we identified no molecular markers in this study to distin- guish between them. Morphological measurements obtained in the field indicate that although a population may have an overall average morphology that defines the variety, some individuals in nearly all populations have putative diagnos- tic characters that define the other variety. The morphological characters used to distinguish the 2 varieties are most likely the result of environmental variability and could result from differences in precipitation and soil water retention. Alternatively, high levels of outcrossing through pollen flow could be obscuring selection for morphological characters at particular sites.

Sampling effort and vegetative cover estimates in sagebrush steppe

Abstract: —The goal of this study was to identify relationships between sampling effort, using a point frame, and the precision of estimates of vegetative cover in sagebrush steppe. Data for 208 point-frame samples were randomly drawn and 95% confidence intervals were identified for varying sample sizes of individual species and species groups. Confidence interval widths decreased rapidly as sample sizes increased from 1 to 50, and more slowly as sample sizes were increased further. For the more abundant species, sample sizes of fewer than 50 frames were sufficient to reduce the 95% confidence interval to less than one-half of average cover. For species with average cover less than 5%, the sample size required to achieve the same relative confidence was much larger. Analyses were repeated to compare point frames with 36 versus 50 sample points per frame. Using a point frame with 50 sample points decreased the number of frames required to achieve the same level of confidence; however, the reduction in sample size was less than the 28% reduction in sample points per frame. Because of the time required to establish transects and position the point frame, it may still be worth sampling more points per frame.

Species richness and california voles in an annual and a perennial grassland

Abstract: Populations of a common burrowing rodent, Microtus californicus (the California vole), thrive in ungrazed or lightly grazed grasslands in coastal California. Two sites ungrazed by livestock, one dominated by native perennial grasses and another dominated by invasive annuals, were evaluated over 2 consecutive years for the relation- ship between plant species richness and location of M. californicus burrow entrances (burrows). Plant species and bur- rows were sampled as present or absent in contiguous 1-m2 quadrats on a 100-m2 grid. Quadrats with burrows averaged significantly more plant species than quadrats without them (11.3 vs. 9.9 species, P < 0.001). Burrows found in 1996 were not correlated with species richness in 1995, suggesting that voles affect richness rather than seek it out. Vole bur- row locations showed significant clumping on the annual site and trended toward clumping on the perennial site in both 1995 and 1996. Because voles seem to create a clumped pattern with their burrow entrances, the associated increase in plant species richness may have a strong effect on the overall structure of the plant community. A quantitative compari- son of the 2 sites showed that the plant matrix of the perennial site contained flora of the annual site. This similarity in plant species composition may allow for similar treatment of our 2 types of sites and potentially other California grass- lands. Undetected increases in vole populations with livestock grazing reduction may account for the erratic results from grasslands management research and the inconsistent success of derived management practices.

A 4000-year record of woodland vegetation from wind river canyon, central wyoming

Abstract: Plant macrofossil analyses of 16 radiocarbon-dated woodrat middens spanning the past 4000 years from the Wind River Canyon region in central Wyoming provide information concerning late Holocene development of juniper woodlands. The study sites are currently dominated by Juniperus osteosperma, with J. scopulorum present locally. Woodlands in the region were dominated by J. scopulorum from ca 4000 yr BP until at least 2800 yr BP. Junipe- rus osteosperma invaded and expanded before 2000 yr BP. This expansion fits a regional pattern of J. osteosperma colo- nization and expansion in north central Wyoming during a relatively dry period between 2800 and 1000 yr BP. At the time the Wind River Canyon region was colonized by J. osteosperma, the species had populations 50-100 km to both the north and south. Long-distance seed dispersal was required for establishment in the study area. Genetic studies are necessary to identify source populations and regions.

Abundance and condition indices of coyotes on Hart Mountain National Antelope Refuge, Oregon

Abstract: —U.S. Fish and Wildlife Service staff at Hart Mountain National Antelope Refuge (HMNAR), southeastern Oregon, documented high pronghorn (Antilocapra americana) fawn mortality, subsequent low fawn recruitment, and declining pronghorn numbers from 1996 to 1999. Coyote (Canis latrans) predation was the primary cause, accounting for 60–85% of fawn mortalities each year, and fawns were not physiologically predisposed to predation. Therefore, we investigated certain coyote population parameters (age structure, survival, density, physiology) to evaluate how or if these factors influence coyote predation rates on pronghorn fawns. We captured 11 coyotes (5 male and 6 female) in December 1998. Age of captured animals ranged from 1.7 to 10.7 yrs (x– = 5.0 years), and all coyotes appeared healthy upon capture. There were no known mortalities through December 1999. We estimated pre-whelping (December through February 1997–1999) density from howling surveys conducted within HMNAR to be 0.40–0.53 km–2. Compared to other published studies, we found significant (P ≤ 0.05) differences in selected blood parameters (e.g., blood urea nitrogen, total protein, white blood cell counts), indicating coyote nutrition may be marginal to deficient during winter at HMNAR. A high percentage of coyotes (91%) tested positive for serum-neutralizing antibodies to canine parvovirus. We judged that parasite (Toxascaris spp., Alaria spp., Sarcocystis spp., and Isospora spp.) prevalence and intensity were not high enough to influence coyote condition. Based on our data, the coyote population at HMNAR is old aged, at a relatively high density, and stable, but their nutrition may be marginal to deficient during winter. Presently, we are unable to draw direct conclusions relating the parameters we sampled with predation rates by this unexploited coyote population.

Flood flows and population dynamics of Arizona sycamore ( Platanus wrightii )

Abstract: Platanus wrightii is a pioneer tree species of warm-temperate riparian deciduous forests in southwestern United States and northern Mexico. Dendrochronological analysis of populations in central and southern Arizona indicated that P. wrightii seedlings establish episodically. Long intervals (10-40 years) elapsed with no apparent establishment. Seedling establishment years were positively associated with winter flood size and annual flow rate, and weakly negatively associated with summer flood size. Large floods sometimes preceded multi-year establishment waves. During the past 2 decades an abundance of winter floods and very wet springs has allowed frequent establishment of P. wrightii . For example, plants established at many sites during the winter flood years of 1993 and 1995, particularly along channels scoured and widened by flood waters. Platanus wrightii also reproduces asexually. Ramets were more abundant than genets in all populations, and ramets established more frequently than seedlings. Ramet density (mean number per genet) varied widely between populations, from 2 (Huachuca Canyon) to 9 (Haunted Canyon), and increased with tree size within 4 of 9 populations. Population size structure varied across a gradient of watershed area. Populations along streams draining the largest watersheds had an abundance of small trees (mean trunk diameter of P. wrightii is influenced by temporal as well as spatial differences in stream flow regimes.

Soil depth effects on Chihuahuan Desert vegetation

Abstract: —We evaluated relationships between soil depth and vegetation standing crop components over a 3-year period on 3 adjoining pastures with similar size, vegetation, and soils on the Chihuahuan Desert Rangeland Research Center in south central New Mexico. Soils on our study pastures are primarily light sandy loams varying from a few centimeters to 1 m or more in depth underlain by a calcium carbonate layer. Study pastures were ungrazed in 1995 and 1996 and conservatively grazed in 1997. Linear regression equations using perennial grass standing crop (kg ha–1) and honey mesquite (Prosopis glandulosa Torr.) cover (%) as dependent variables and soil depth as the independent variable were significant (P <0.05) and similar for all 3 pastures. Deep soils had low perennial grass standing crop and high mesquite cover, while the opposite occurred for shallow soils. Within shallow soils, honey mesquite and perennial grass standing crop were not correlated (P = 0.78, n = 18), but a significant (P = 0.01) negative correlation occurred on deep soils (r = –0.67, n = 15). Perennial grass standing crop differed greatly among years when data were pooled across pastures, ranging from 64 kg ha–1 in 1995 to 248 kg ha–1 in 1997. Our study shows that soil depth has a major influence on Chihuahuan Desert vegetation. Perennial grasses are favored by shallow sandy soils while deep sandy soils favor honey

Three naturally occurring Penstemon hybrids

Abstract: Three wild Penstemon hybrids are documented herein: Penstemon clevelandii × spectabilis, P. centranthifolius × spectabilis , and P. centranthifolius × eatonii . Each putative hybrid was compared to its respective parental species using manifold floral and vegetative characters for which the parents differed. For each hybrid hypothesis, characters were counted as being intermediate or not intermediate. There were significantly more intermediate characters in all 3 cases (one-sided sign tests, P Penstemon species evidently do hybridize naturally, and for nearly all characters the hybrids are consistent with the view that the parents differ largely by additive genetic effects.

Geographic variation in pelage color of piñon mice ( Peromyscus truei ) in the northern Great Basin and environs

Abstract: —Cluster analyses of values for hue, value, and chroma (based on Munsell soil-color charts) obtained at 6 points on pelages of 202 adult piñon mice (Peromyscus truei) from the northern Great Basin and environs produced dendrograms with specimens grouped into 5 clusters. In most instances distribution of specimens forming clusters reflected those published for nominal races. In instances in which previous distributions of nominal races were not supported and for specimens previously unclassified, geographic distribution of groups of color morphs was logical and suggested avenues for additional research on geographic variation in the species.

Late Pleistocene mollusks from the southern Black Hills, South Dakota

Abstract: Pleistocene-age mollusks recovered from the Nelson-Wittenberg Site and Mammoth Site provide information on paleoenvironments of the southern Black Hills, South Dakota. New mollusk records for the Mammoth Site include Vertigo modesta, Catinella sp., and Gyraulus parvus . The presence of V. modesta, Columella columella alticola , and Pupilla muscorum at the Nelson-Wittenberg Site suggests cooler than modern conditions in the Black Hills during the Pleistocene. Although the majority of identified taxa are consistent with previous interpretations of an arid, shrubsteppe environment for the Black Hills during the Wisconsin Glaciation, V. modesta and C. c. alticola suggest the presence of at least some isolated, local mesic areas.

Assessment of cryptobiotic crust recovery

Abstract: Chlorophyll a and b analyses of cryptobiotic crusts from burned and unburned sites on the Snake River plain provided an estimate of crust recovery. In less than 3 years, chlorophyll a levels were approximately 50% of the unburned reference site. Chlorophyll a/b ratios indicated that the biotic composition of the recovering cryptobiotic crust consisted largely of eukaryotic algae and bryophytes.

Autumnal migration of Eared Grebes ( Podiceps nigricollis ) through southwestern Wyoming: a key to assessing the size of the North American population

Abstract: —In autumn the vast majority of the North American population of Eared Grebes (Podiceps nigricollis) congregates for several months at Great Salt Lake, Utah, and Mono Lake, California. Because the lakes are so large, it has not been possible to monitor grebe migration with sufficient accuracy to determine when peak numbers are reached. To clarify migration phenology, we analyzed data from 2 isolated wetland areas in southwestern Wyoming where grebes land en route between breeding areas in the interior and Great Salt Lake. Occasional birds, probably nonbreeders or failed breeders, begin moving southward as early as mid-June. Migration of postbreeding birds starts in late July, peaks in late August and September, and is largely completed by the end of October, with very small numbers arriving into November. The pattern of migration and number of birds encountered varied annually, but 95% of the migration was usually completed by 15 October. As a result, censuses at the major staging lake made on or after 15 October but before the grebes depart for wintering areas can be used to study trends in size of the North American pop-