We examined how plant traits related to growth and resource use have evolved during hybrid speciation and specialization into stressful habitats. Two desert sunflower species of homoploid hybrid origin are endemic to habitats with lower soil nutrient levels than those of their ancestral parent species. We hypothesized that the hybrid species would exhibit greater tolerance to low levels of soil nutrients than their parental species. The 2 hybrid species, Helianthus anomalus and H. deserticola, and their parental species, H. annuus and H. petiolaris, were compared for plant traits and growth through reproduction under 3 nutrient levels in a greenhouse study. An additional seedling study compared species for maximum seedling relative growth rate under optimum conditions. The hybrid species did have greater tolerance of nutrient limitation than the parental species, demonstrated by a resistance to change in stem height and diameter growth across treatments. A similar trend was observed in total biomass at final harvest. This ability to maintain growth may be partially explained by maintained investment in photosynthetic enzymes regardless of nutrient treatment. Though the hybrid species were more tolerant of nutrient stress, differences in the hybrid response to nutrient stress compared to the parental species' response were much smaller than expected from habitat comparisons. Helianthus anomalus has evolved a classic stress-tolerant phenotype, having long leaf lifespan, tough leaves, and slower early seedling relative growth rate. While both hybrid species have a conservative growth strategy, which confers greater stress tolerance than the parental species possess, functional trait differences among the hybrids suggest that the 2 species have experienced vastly different selective pressures.

Use of herbicides to thin dense stands of Artemisia spp. (sagebrush) can free up resources for herbaceous plants and increase forage production, but may also facilitate weed invasion. We revisited a sagebrush thinning experiment in a north central Wyoming big sagebrush–grassland 11 years after application of tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N-N′-dimethylurea) to determine the long-term responses of shrubs, available soil resources, perennial grasses, and Bromus tectorum L. (downy brome). Tebuthiuron reduced shrub cover by more than half, from 31% in untreated plots to 15% in treated plots (P = 0.002), and increased downy brome cover approximately 4-fold, from 0.9% in untreated plots to 3.5% in treated plots (P = 0.02). Treatment with tebuthiuron also resulted in marginally significant increases in cover of perennial grasses (from 9% to 12.3%; P = 0.07) and bare ground (from 39.1% to 43.9%; P = 0.08). In comparisons of resource availability among microsites, available NO₃ was higher under dead sagebrush than under live sagebrush (P = 0.03). No significant differences in soil water content were detected. The relatively recent expansion of downy brome populations at this site and the high NO₃–N levels observed under dead sagebrush suggest that conditions facilitating downy brome invasion may persist for many years following sagebrush thinning. We demonstrate that sagebrush thinning can cause increases in downy brome populations years after initial treatment and suggest that managers should use caution when considering thinning sagebrush if downy brome is present, even if initial populations are small.

Seed harvesting ants (Pogonomyrmex rugosus) concentrate organic matter and nutrients near their nests and create biogeochemical hotspots in desert soil. We examined factors regulating denitrification and soil respiration in a Mojave Desert ecosystem to determine the role harvester ant colonies play in nitrogen loss and carbon mineralization. Organic matter and nutrient storage were significantly greater in colonies than under the dominant vegetation (i.e., Pleuraphis rigida, a bunch grass) and in bare soil, with standing stocks of inorganic nitrogen in colonies nearly 4-fold greater than in the other microhabitats. Soil respiration, measured with laboratory incubations, was below detection limits under ambient soil conditions. Respiration rate in soil from bare patches and under grass was limited by water and labile organic carbon, with secondary nitrate limitation evident only once carbon limitation was alleviated. Soil respiration in ant nest soil was limited by water and labile organic carbon only. Denitrification, measured by the acetylene block technique, was elevated in bare soil and under grass with the addition of nitrate. Ant nest soil also responded to a nitrate addition; however, denitrification rate was greatest with addition of glucose. Ordinarily desert soil has low rates of respiration and denitrification due to dry ambient conditions. However, ant colonies likely function as important sites for nitrogen loss and carbon mineralization following rain storms, especially if storms coincide with seed set and the temporally pulsed input of organic matter into colonies.

Larval and juvenile stages of many fishes require nursery habitats that provide optimal conditions for growth. Loss or degradation of these habitats limits recruitment, causing population and species declines. Least chub (Iotichthys phlegethontis), an endemic cyprinid in the Bonneville Basin, is currently restricted to a few spring complexes in Utah. This species utilizes the warm shallow spring margins as spawning and rearing habitat throughout the summer. This study was conducted to determine effects of temperature on survival and growth of age-0 least chub to understand the importance of temperature in selection of spring margins as rearing habitat. Age-0 least chub were exposed to 5 temperatures (14°C, 17°C, 21°C, 24°C, and 27°C) for 112 days. Growth rates varied significantly with temperature except at 17°C and 27°C, and growth rates were highest at 21°C (P < 0.001). Maximum growth rate for age-0 least chub, estimated from a 2nd-order polynomial regression, would occur at 22.3°C. These thermal requirements indicate the importance of warm rearing habitats in producing strong year classes and viable populations. However, warm spring margins also enable western mosquitofish, a nonnative competitor and predator of least chub, to thrive in these spring habitats. Broad thermal limits of the least chub suggest that it could persist at cooler temperatures, which would reduce the viability of western mosquitofish populations.

Interactions of Artemisia tridentata ssp. vaseyana (mountain big sagebrush) and neighboring herbs may affect community development following fire in sagebrush steppe. Dry mass, photosynthesis, and water relations were measured for seedlings of A. tridentata ssp. vaseyana occurring at different distances from neighboring herbs in the initial growing seasons following fire, when herbs dominate plant community cover. Seedling mass significantly increased as distance to neighboring herbs increased, although a low r² indicated that mass was also affected by other sources of variation. Carbon assimilation (A_net) was also greater for A. tridentata ssp. vaseyana seedlings in microsites farther from herbs, except during those sampling dates when A_net and water availability were at low levels. Contrary to our expectations, water status of seedlings was not correlated with their distances to neighboring herbs, and supplemental watering did not affect the slope of the relationship between seedling mass and distance to neighboring herbs. These findings suggest that negative relationships between A. tridentata ssp. vaseyana seedlings and herbs establishing after fire are not likely due to competition over water and may instead result from interactions over factors not measured here (e.g., nutrients).

We evaluated wildlife use of witches' brooms associated with infection by Douglas-fir dwarf mistletoe (Arceuthobium douglasii) in 6 mixed-conifer study areas in Arizona and 2 areas in New Mexico. We climbed 153 infected Douglas-firs (Pseudotsuga menziesii) and examined 706 witches' brooms for evidence of wildlife use. Even though we observed evidence of use by birds, most wildlife use was by small mammals, particularly red squirrels (Tamiasciurus hudsonicus). Red squirrels used witches' brooms for nesting, foraging, caching, and as latrines. Witches' brooms classified as Type II or III brooms, located close to the main bole with large platforms, and 5–10 m above the ground were the most frequently used by red squirrels.

Two rare endemic carnivores occur on California's northern Channel Islands: island spotted skunks (Spilogale gracilis amphiala) and island foxes (Urocyon littoralis). As insular carnivores, both may be particularly vulnerable to novel pathogens. We tested sera from 31 island spotted skunks on Santa Cruz Island, where both skunks and foxes occur sympatrically, to establish their exposure to disease agents. One skunk (3%) tested positive for canine heartworm, and 3 skunks (10%) tested positive for canine parvovirus. None showed evidence of exposure to canine adenovirus, canine distemper virus, canine herpesvirus, Leptospira bacteria (serovars pomona, canicola, and icterohaemorrhagiae), or pseudorabies virus. Spotted skunks on Santa Cruz Island apparently have low susceptibility or exposure to these pathogens and are unlikely to be reservoirs of these diseases for island foxes.

The dorsal skin gland appears to be a sexually dimorphic character for all species of Dipodomys; however, this feature has not been characterized for most taxa. Previous studies of several species have demonstrated the histological uniqueness of the gland in D. spectabilis. Other attempts to correlate seasonal variation in gland size with reproductive patterns have met with mixed success. An examination of the dorsal skin glands of 333 museum study skins of adult Dipodomys elator demonstrated a July–August size decrease in both sexes, although the glands of males were larger and more variable in size than those of females. Gland size of males was positively correlated with testes measurements, and the data for females, though more limited, suggested that postpartum individuals exhibited greater gland development than pregnant animals. Histological samples demonstrated that the fully developed dorsal skin gland in D. elator consists of about 100 individual secretory units, is similar to 5 other species of kangaroo rats (D. agilis, D. deserti, D. merriami, D. ordii, D. panamintinus; Quay 1954), and is markedly different than that of D. spectabilis. We present a histological description of the dorsal gland of juveniles and the underlying panniculus dorsalis.

Herbivory is an important ecological process in forest canopies but is difficult to measure, especially for whole stands. We used the Wind River Canopy Crane in Washington State to access 101 randomly-located sample points throughout the forest canopy. This provided a relatively quick and convenient way to estimate herbivory for a whole stand. The overall level of herbivory was estimated at 1.6% of leaf area. The distribution was strongly skewed to the lower canopy where broad-leafed species experienced higher levels of herbivory. Herbivory averaged 0.3% in conifers and 13.5% in broad-leafed species. Fully half of the sample points had no detectable herbivory. Herbivory in this old-growth conifer forest is among the lowest levels published for forests around the globe and may reflect the general levels of herbivory in temperate coniferous forests during nonoutbreak conditions. Our whole-stand estimate is the first attempt at measuring herbivory for an entire forest stand in the Pacific Northwest.

Piute ground squirrels (Spermophilus mollis idahoensis) are normally above ground from late January until late June or early July in the Snake River Birds of Prey National Conservation Area in southwestern Idaho. In 2002 they were rarely seen above ground after early May. Because of the ecological importance of ground squirrels for nesting raptors and other species, we sought to determine the reasons for their early disappearance. We sampled 12 sites from January 2003 through March 2003 to determine if a population crash had occurred in 2002. Tests indicated that Piute ground squirrels had not been exposed to plague within the past year. The presence of yearlings in the population indicated that squirrels reproduced in 2002 and that at least some yearlings survived the winter. Both yearling and adult squirrels appeared to be reproducing at or above normal rates in 2003. The most plausible explanation for the early disappearance of Piute ground squirrels in 2002 is that squirrels entered seasonal torpor early in response to a late spring drought. In addition, the breeding chronology of squirrels may have shifted during the past 2 decades in response to climate change and/or habitat alteration. Shrub habitats provide a more favorable and stable environment for squirrels than grass habitats. Squirrel abundance was higher on live-trapping grids with sagebrush than on grids dominated by grass, and squirrel masses were higher at sites dominated by shrubs and Sandberg bluegrass (Poa secunda). Densities in big sagebrush (Artemisia tridentata) were within the ranges reported for earlier years, but densities in grass were lower than previously reported. Low densities at grassland sites in 2003 support other findings that drought affects squirrels in altered grass communities more than those in native shrub habitats. Long-term shifts in ground squirrel breeding chronology may have implications for raptors that depend on them for food.

We describe ontogenetic patterns in the diets of shortnose and Lost River suckers (15.8–92.8 mm standard length) from Upper Klamath Lake in summer 1999. Both species made a transition from surface and planktonic prey to benthic prey at about 20–30 mm standard length, corresponding to the approximate size of the juvenile morphological transition. Surface prey was dominated by adult chironomids and undigestable pollen, while benthic prey was dominated by larval chironomids, chydorids, and ostracods. In the 15–20-mm size class, pollen made up >75% of food particles in 68% of specimens, and only 2 specimens in this size class lacked any pollen grains. A better understanding of the prey selection process in larval suckers is needed to determine the importance of this potential source of starvation. The planktonic prey eaten during the surface-to-benthic feeding transition were widely distributed in the lake, suggesting that larvae use emergent vegetation primarily as a refuge from predators. On a numerical basis, crustaceans and larval chironomids contributed most to the diets of larger juveniles. In specimens >40 mm, shortnose suckers ate more Tanytarsini and Lost River suckers ate more chironomid pupae and chydorids. In specimens >40 mm there was a strong habitat-related difference in diet: specimens collected in offshore samples ate more chironomid larvae and pupae, harpacticoid copepods, and chydorids, whereas onshore specimens ate more cyclopoid copepods and invertebrate eggs. The transition from onshore to offshore habitat appears to occur over a broad size range of about 40–90 mm.

Vegetation trends due to climatic changes are difficult to separate from disturbances caused by varying land uses. To separate climatic influences from livestock grazing and fire disturbances within sagebrush steppe, we compared vegetation structure and productivity during 2 periods (10-year sequences of data from the late 1950s to the late 1960s and 3 years in the early 1990s) at 12 stands within 3 relict areas in or near the Great Rift of southern Idaho. Year-to-year fluctuations in annual net aboveground phytomass accumulation (ANAPA) were considerable in response to varying climate during both periods. More importantly, an apparently significant increase in ANAPA was observed during the latter study period. However, this apparent increase may have been due to the unusually wet conditions of 1993. Throughout both study periods, ANAPA was even more positively correlated with species richness than with precipitation, although both influences were statistically significant. Aggregation of these data by plant growth forms showed that shrubs, particularly sagebrushes, have progressively increased their proportion relative to herbaceous understory. This directional (successional) change in the proportional contributions of growth forms to ANAPA was probably due more to long-term absence of fire at these isolated locations than to any detectable climate change or lack of grazing. This finding reduces our confidence in the use of such areas as reference sites for monitoring or as living examples for restoration efforts, but it does increase our understanding of vegetation dynamics within sagebrush steppe.

Acronyms.–ANAPA–annual net aboveground phytomass accumulations, ANOVA–analysis of variance, ANPP–aboveground net primary production, COV–coefficient of variation, CY–crop year, CYP–crop-year precipitation, ES–ecological site, MANOVA–multivariate analysis of variance, MAT–mean annual temperature, NRCS–Natural Resources Conservation Service, PDSI–Palmer Drought Severity Index, RUE–rainfall use efficiency.