Diet of the Mogollon vole as indicated by stable-isotope analysis (δ 13 C and δ 15 N)

There are no published studies on the diet of Mogollon voles ( Microtus mogollonensis ) although this species occurs throughout the Southwest in montane forestlands. Mogollon voles are believed to be herbivorous, selecting the vegetative portion of grass as their dominant food source. Herbivores frequently select more easily digested C 3 plants over C 4 plants; we thus expected Mogollon voles would feed primarily on C 3 plants. We collected hair samples from Mogollon voles captured in northern Arizona between 1967 and 2003 and plant samples from some capture sites. Then we compared stable carbon (δ 13 C) and nitrogen (δ 15 N) isotope ratios to investigate dietary preferences for C 3 or C 4 plants. Mean isotope ratios for C 3 plants we sampled were –26.84‰ ( s = 0.17) for δ 13 C and –0.02‰ ( s = 0.32) for δ 15 N. For C 4 plants, mean isotope ratios for δ 13 C and δ 15 N were –15.04 ‰ ( s = 0.38) and –0.74‰ ( s = 0.55), respectively. Mogollon voles were largely herbivorous based on δ 15 N (mean and standard error: 3.77 ± 0.17‰) and used C 3 plants more than C 4 based on δ 13 C (–24.21 ± 0.14‰). Activities that lead to changes in plant species composition or reduction in C 3 plants in montane grasslands and forests (e.g., excessive ungulate grazing) may reduce habitat quality for Mogollon voles.     

Response of tree ring holocellulose δ 13 C to moisutre availability in Populus fremontii at perennial and intermittent stream reaches

We measured δ 13 C of tree ring holocellulose to assess intra- and interannual variation in integrated leaf gas exchange responses of Frémont cottonwood ( Populus fremontii ) to monsoonal moisture inputs in southeastern Arizona. We predicted that δ 13 C of trees growing along drought-susceptible intermittent reaches of this semiarid river system would be more responsive to monsoonal moisture inputs than trees found along perennial reaches, where groundwater is consistently available. We sampled stem xylem cores from 7 trees, each at an intermittent and perennial reach of the San Pedro River near Tombstone, Arizona. We identified and subdivided individual rings from 1990 to 2000. δ 13 C of holocellulose from these subdivisions was compared with precipitation amount, atmospheric vapor pressure deficit ( D a ), and 90% exceedence flows ( Q 90 ) calculated from seasonal flow duration data. δ 13 C values were higher at the intermittent reach than at the perennial reach. Furthermore, annual ring δ 13 C values at the perennial reach were not correlated with stream flow, precipitation, or D a . δ 13 C values for trees at the intermittent reach were negatively correlated with monsoon stream flow, precipitation, or D a . δ 13 C values for trees at the intermittent reach were negatively correlated with monsoon season (1 July-15 September) Q 90 ( r 2 = 0.50, P = 0.015) and positively correlated with D a ( r 2 = 0.45, P = 0.03). Shifts in δ 13 C between the inner- and outer-third of the annual ring were used as a measure of intra-annual variation. These shifts were correlated with monsoon season D a ( r 2 = 0.57, P = 0.01) and Q 90 ( r 2 = 0.59, P = 0.005) for trees growing along the intermittent reach. Intra- and interannual variation in integrated photosynthetic response exists at the population-scale for these native, riparian forests. Changes in monsoonal precipitation and stream flow may differentially alter photosynthetic gas exchange of P. fremontii and function of these riparian ecosystems.     

C 3 and C 4 Species Changes Identified by δ 13 C values of soil organic matter in a Colorado prairie

We measured carbon isotope signatures (δ 13 C) from 0-10 cm and 10-20 cm soil depth intervals for grassland soils near Boulder, Colorado. These grasslands included tall-, short-, and mixed-grass prairies that were grazed, ungrazed, or hayed. Soils exhibited δ 13 C signatures consistent with observations that current sites are a mix of C 3 and C 4 species, with C 3 plants more abundant in mixed-grass than in native tall- or shortgrass prairies. The δ 13 C signatures were not significantly different for grassland types; however, management treatments (grazing, no grazing, haying) significantly influenced changes in soil δ 13 C signatures from the 0-10 cm to 10-20 cm soil depth intervals. We observed a correlation ( r = 0.63) between isotopic values of surface soils and percent native species in total vegetation cover. Overall, the community type with the lowest percentage of nonindigenous species cover had the most enriched δ 13 C signature. Sites currently grazed by prairie dogs, cattle, or both herbivores had stronger C 3 signatures, indicating that grazing may have increased C 3 plant productivity in these communities at the expense of C 4 grasses. This finding differs from studies of native shortgrass steppe where grazing has the opposite effect on the relative abundance of these 2 functional groups of plants. This result, along with the correlation between C 3 isotopic values and nonnative vegetation abundance, provides evidence that management practices that maintain dominance of C 4 grasses should be encouraged.     

Carbon isotope discrimination in the C 4 shrub Atriplex confertifolia along a salinity gradient

Carbon isotope discrimination (Δ) was measured for leaves of Atriplex confertifolia along a salinity gradient in northern Utah. Over this gradient, the variation of Δ values was high for a C 4 species, and the Δ values were positively correlated with salinity in both years of study. Of the possible explanations for this patter, the Δ results are consistent with the notion that salinity induces an increase in the bundle sheath leakiness of these C 4 plants.     

Competition and niche partitioning among Pseudoroegneria spicata, Hedysarum boreale , and Centaurea maculosa

Maximizing desired plant diversity has been suggested as a means of minimizing non-indigenous plant invasion on rangeland by maximizing niche occupation. Competition between 2 desired indigenous species, Pseudoroegneria spicata (Pursh). L?ve (bluebunch wheatgrass) and Hedysarum boreale Nutt. var. boreale (northern sweetvetch), and a non-indigenous invader, Centaurea maculosa Lam. (spotted knapweed), was quantified using growth of isolated individuals and 2 three-species addition series experiments. Seeding densities of P. spicata remained constant at 0, 200, 400, and 800 seeds m -2 in both experiments. H. boreale and C. maculosa seeding densities were 0, 200, 400, and 800 seeds m -2 , respectively, in the 1st experiment and 0, 400, 800, and 1600 seeds m -2 , respectively, in the 2nd experiment. Densities were factorially arranged. Pots were place in an environmental chamber (12 C, 12-h day length, 200 μmol photons m -2 s -1 spectral light) in a randomized-complete-block design. After 90 d the growth rate of P. spicata (92.1 mg d -1 shoot growth) was greater than that of the 2 forbs (1.6 and 5.5 mg d -1 for H. boreale and C. maculosa , respectively), and growth rates of the 2 forbs were similar to one another. Curvilinear regression indicated that intraspecific competition was more important in determining shoot weight than intraspecific competition. In addition, the 2 forbs competed more directly with each other than with P. spicata . Competition coefficient ratios (1.42 and 1.53 for P. spicata with H. boreale and C. maculosa , respectively, and 1.03 for H. boreale with C. maculosa ) indicated substantial partitioning of resources between P. spicata and each of the forbs. Little or no resource partitioning occurred between forbs. This study suggests that increasing desired plant diversity may minimize weed invasion by increasing niche occupation.     

Roadside foraging by kangaroo rats in a grazed short-grass prairie landscape

We used live-trapping and foraging experiments to describe use of roadside vegetation by kangaroo rats ( Dipodomys ordii ) in short-grass prairie in Colorado, and to determine whether this species' perception of predation risk differed between roadside habitats, where predators were expected to be most active, and locations 120 m into adjacent grazed pastures. Giving-up densities (GUDs) were measured in paired seed trays placed beneath saltbush ( Atriplex canescens ) shrubs and in the open, 3 m from shrubs along transects in roadside and pasture locations. Trials were conducted on nights with a partial (1st-quarter), full, and new moon to assess how intensity of risk affected microhabitat use. Kangaroo rats were much more abundant in areas with saltbush cover than in grazed prairie, and were 4–6 times more numerous along roadsides in saltbush areas than in other locations. On dark nights and in pasture locations, foraging rates of kangaroo rats were similar in shrub trays and open trays. The fewest seeds were removed (i.e., GUDs were highest), however, in open trays along roads on moonlit nights, suggesting that kangaroo rats recognized potential risks associated with roadsides on bright nights. The high numbers of kangaroo rats along roads suggest that benefits associated with these habitats (ease of digging, dust bathing, higher soil seed banks) exceed the costs associated with higher risk of mortality from predators and vehicles. Our results demonstrate how foraging decisions differ depending on the spatial and temporal contexts in which behaviors are measured, and underscore the potential value of less common habitats such as road margins for increasing landscape-scale diversity and wildlife habitat in grazed grasslands.     

Long-term fire history in Great Basin sagebrush reconstructed from macroscopic charcoal in spring sediments, Newark Valley, Nevada

We use macroscopic charcoal analysis to reconstruct fire history in sagebrush ( Artemisia tridentata var. wyomingensis and A. tridentata var. tridentate ), in Newark Valley, Nevada. We analyzed charcoal at continuous 1-cm intervals (～7-127 years), and pollen at 2- to 10-cm intervals (～70-263 years) in a core spanning the last 5500 cal yr BP (calendar years before present). A charcoal peak in the historic period was associated with a >1400-ha fire dated to 1986 that burned in the watershed. We reconstructed the prehistoric fire history by inferring fires from similar charcoal peaks that were significantly greater than the background charcoal accumulation. Our results suggest the fire regime is climate and fuel driven. During periods of wetter climate, sagebrush increased and fires were more abundant, and during extended dry periods when sagebrush decreased, fires were less frequent. Our method does not allow calculation of a fire-return interval; however, our results support models that estimate a mean fire-return interval of up to a century in Artemisia tridentata var. wyomingensis . The charcoal record indicates that fires have increased within the historic period. This contrasts with pinyon/juniper studies that indicate an expansion of woodland associated with fewer fires in the historic period. We suggest that in the central Great Basin, a regime of frequent fires in sagebrush that limits woodland expansion is true for the sagebrush-woodland ecotone, but in sagebrush-dominated valleys with lower fuel loads, fires have always been less frequent. Protecting sagebrush-dominated valleys from frequent fire would appear to be consistent with the prehistoric fire regime.     

A comparison of mosquito consumption and prey selection between least chub ( Iotichthys phlegethontis ) and western mosquitofish ( Gambusia affinis )

We compared mosquito consumption and prey selection between least chub ( Iotichthys phlegethontis ) and western mosquitofish ( Gambusia affinis ) to determine the potential of least chub as an indigenous replacement for mosquito control in Utah. Mosquito consumption was compared between the 2 species in 2 experiments. The first tested consumption at 3 ratios of pupae and larvae ( Culex sp.; 1:3, 3:4, and 1:1), and the second tested consumption at varying densities of larvae (967 larvae ? m–3 , 1354 larvae ? m–3 , and 2258 larvae ? m–3 [30, 42, and 70 larvae per 31-L tank, respectively]). Western mosquitofish consumed more mosquitoes at lower pupae-to-larvae ratios than least chub, but least chub consumed more mosquitoes as the ratio of pupae to larvae increased. Western mosquitofish consumed significantly more larvae than least chub at all densities. Prey selection was compared between least chub and western mosquitofish, either individually or in intraspecific pairs, when the fish were fed equal abundances of 3 prey items: mosquito larvae, Daphnia magna , and midge larvae ( Chironomid sp.). Least chub consumed significantly fewer total prey items for both the 1- and 2-fish trials; western mosquitofish consumed significantly more individuals of each prey type except for Daphnia magna in the 1-fish trials. Least chub and western mosquitofish demonstrated no selection for prey items, indicating that both fish would consume mosquito larvae at rates relative to abundance. Feeding habits demonstrated in this study indicated that least chub could be a potential replacement for western mosquitofish for mosquito control; however, field studies should be conducted to assess the ability of both species to control mosquitoes in a natural setting.     

Carbon isotope discrimination and water relations of oak hybrid populations in southwestern Utah

The evergreen oak Quercus turbinella and the deciduous Q. gambelii form natural hybrids in southwestern Utah and northern Arizona. Hybrid individuals also are found in northern Utah in a region where only Q. gambelii currently exists, indicating that Q. turbinella has recently retreated southward. Our objectives were to (1) examine the ecophysiology of parental taxa and hybrids under natural conditions in southeastern Utah, and (2) investigate the level of integration between leaf carbon isotope discrimination (a synthetic gas exchange trait) and structural and chemical traits of leaves in morphologically variable hybrid populations. Leaf length, width, mass-to-area ratio (LMA, g m -2 ), and nitrogen concentration (N, g g -1 ) within 2 hybrid populations near New Harmony, Utah, were highly intercorrelated. Variation within the hybrid populations spanned mean values for these traits observed in parental taxa from adjacent ""pure"" populations of each species. Carbon isotope discrimination (Δ), an integrated measure of the ratio of intercellular to ambient CO 2 concentration, ranged from 16.1‰ to 19.6‰ within the 2 hybrid populations and was positively correlated with leaf nitrogen concentration and negatively correlated with LMA; individuals in hybrid populations with leaves resembling Q. gambelii had the highest leaf Δ and N concentrations and lowest LMA compared with leaves from plants that resembled Q. turbinella . CO 2 uptake is limited by stomatal conductance and possibly by mesophyll resistance to a greater extent in Q. turbinella phenotypes than in intermediate or Q. gambelii phenotypes. δD of stem xylem water (an indication of active rooting depth) and predawn water potential during the peak monsoon period in August were not correlated to leaf Δ values within the hybrid populations. Several individuals that were morphologically similar to Q. turbinella in the hybrid populations maintained high predawn water potentials and derived moisture from winter recharge that presumably was taken from deep soil layers. Apparently, a few adult individuals of the Q. turbinella phenotype in hybrid populations accessed water from deep in the soil profile, which enabled them to avoid summer drought. Reduced monsoonal activity may have been an important, but not the single, determinant of Q. turbinella s retreat from northern Utah during the recent Holocene.     

Captures of Crawford's gray shrews ( Notiosorex crawfordi ) along the Rio Grande in central New Mexico

We captured >2000 Crawford’s gray shrews ( Notiosorex crawfordi ) in a riparian forest mainly consisting of cottonwoods ( Populus deltoides ) along the Rio Grande in central New Mexico. Little has been published about abundance and habitat of Crawford’s gray shrew throughout its distributional range. During 7 summers, we captured shrews in pitfall traps at 13 study sites in Bernalillo, Valencia, and Socorro counties. Capture rates of shrews were greatest in August and September, and we did not detect a response of shrews to restoration treatments that removed nonnative plants from riparian forests. Results from our study indicate that (1) Crawford’s gray shrews are more abundant in riparian habitats than historically presumed and (2) pitfall traps with drift fences are an effective means to capture shrews.     

Large mixed-species dispersal flights for predatory and scavenging aquatic Heteroptera and Coleoptera, northern Arizona, USA

We report 4 incidents of large (hundreds to hundreds of thousands of individuals) mixed-species flights of predatory and scavenging aquatic Heteroptera and Coleoptera. The events occurred on normal (mostly clear, calm) autumn 2005 and spring 2006 late afternoons near Flagstaff, Arizona. Flight days were either near the full moon or in advanced waning lunar periods. At least 18 species were involved in the flights, with as many as 16 species (7 species of Heteroptera in 3 families, 9 species of Coleoptera in 2 families) in a single flight. Heteroptera (especially from the family Corixidae) were 2–4 orders of magnitude more numerous than Coleoptera. The diasporas plummeted, with much direct mortality, onto green metal roofs, and the largest event lasted more than 2 hours. Even after 2 days, uninjured individuals failed to resume their flights. The literature suggests that such flights occur for autumn movement to winter habitats or for location of springtime habitats for reproduction. The relative proportions of species in flocks were similar neither to the relative proportions in the region nor to those in nearby livestock watering tanks, indicating that the flights consisted of nonrandom assemblages of species. These events are rare or unique observations of coordinated movement of mixed predatory and scavenging invertebrate species.     

Implications of polyploidy in the host plant of a dipteran seed parasite

Although polyploidy can alter host plants in important ways (e.g., size, phenology, resource use, and ecological range), little is known about the effects of polyploidy-associated changes on plant-insect interactions. The presence of Campiglossa footeorum Novak (Diptera: Tephritidae) and its effect on its host plant Arnica cordifolia Hook. (Asteraceae) were monitored throughout Colorado, where triploids and tetraploids of the host plant occur. Campiglossa footeorum is more abundant in sites with more tetraploids and attacks tetraploids more than triploids. Polyploidy could be an important force shaping the current evolutionary trajectory of the plants and insects in this system. Campiglossa footeorum is intimately linked to A. cordifolia , and polyploidy should be included in any assessment of the insect’s population dynamics.     

Diets of sympatric bobcats and coyotes during years of varying rainfall in central Arizona

We collected fecal samples (scats) of sympatric bobcats ( Lynx rufus ) and coyotes ( Canis latrans ) between 2000 and 2003 in a 53,600-ha area of the Upper Sonoran Desert in central Arizona. Our objective was to investigate composition, diversity, and overlap of diets of bobcats and coyotes in relation to varying rainfall in the Sonoran Desert of central Arizona. In general, bobcats ate more rodents than did coyotes, and coyotes ate more lagomorphs, large prey, and fruit/seeds than did bobcats. Composition of bobcat diets was independent of differences among years in annual rainfall and seasonal rainfall during summer–autumn (May–October) and winter–spring (November–April). Composition of coyote diets also was independent of drought conditions among years during summer–autumn, but coyotes ate more large prey and fewer rodents during years with winter–spring drought. Seasonally, bobcats ate more rodents than did coyotes in summer–autumn and winter–spring, whereas coyotes ate more lagomorphs than did bobcats during winter– spring, and more large prey and fruit/seeds in both seasons. Coyotes ate more large prey and lagomorphs during winter–spring, when seasonal rainfall was higher, and more fruit/seeds in summer–autumn, when seasonal rainfall was lower. Diversity of diets was consistently higher for coyotes than for bobcats, and increased for bobcats but not for coyotes during winter–spring drought and during higher seasonal rainfall in winter–spring. Overlap of diets between predators was independent of rainfall levels. We suggest that bobcats in the Sonoran Desert are more selective, specialized predators and that coyotes are more generalist, opportunistic predators. We hypothesize that, although diversity of bobcat food items and composition of coyote diets differ with varying rainfall in the Sonoran Desert, patterns of feeding strategy are independent of seasonal differences in precipitation and effects of drought, and bobcats and coyotes partition food resources independently of varying rainfall.     

Late Quaternary vegetation and climate in the Escalante River Basin on the central Colorado Plateau

Five alcoves (rock shelters) in the Forty-Mile Canyon—Willow Gulch area of the Escalante River Basin in southeastern Utah yielded rich deposits of late Quaternary macrobotanical remains. The deposits were sampled and the contents identified in order to construct a chronology of vegetational change. Fourteen radiocarbon dates indicate that the fossils were deposited between 12,690 and 7510 yr B.P. (years before present). Ninety-one plant taxa were identified, 62 to species. Six species were common to all alcoves: Gambel oak ( Quercus gambelii ), box-elder ( Acer negundo ), prickly pear ( Opuntia subgenus Platyopuntia), skunkbush ( Rhus aromatica var. trilobata ), serviceberry ( Amelanchier utahensis ), and Indian ricegrass ( Oryzopsis hymenoides ). Late Pleistocene samples (>11,000 yr B.P.) contain extralocal, elevationally depressed species such as Douglas fir ( Pseudotsuga menziesii ), spruce ( Picea sp.), and mountain mahogany ( Cercocarpus ledifolius ), and mesophytic species such as rose ( Rosa woodsii ) and water birch ( Betula occidentalis ). Early Holocene samples (11,000-8000 yr B.P.) contain no elevationally depressed conifers, and the remaining mesophytic species decrease in relative abundance. Reticulated hackberry ( Celtis reticulata ) becomes common. The terminal Early Holocene sample (8000-7000 yr B.P.) contains abundant Gambel oak and prickly pear, but little else. Paleoclimatic interpretations for the Late Pleistocene correspond well to those of most other workers on the Colorado Plateau. Climates that were wetter and at least seasonally cooler than they are today are inferred from the macrobotanical assemblage. However, the increased moisture is attributed to higher stream base levels and increased groundwater rather than directly to increased precipitation. Early Holocene climates are interpreted as warmer and drier than those of the Late Pleistocene but still wetter than the present climate. Groundwater levels appear to be decreasing due to stream entrenchment. Terminal Early Holocene climates were much warmer and at least seasonally drier. By the end of the period, groundwater levels had decreased so much that the alcoves were unable to sustain plant communities; stream base level was probably near the present level.     

Condition models for wintering Northern Pintails in the Southern High Plains

Three condition models for wintering Northern Pintails ( Anas acuta ) were tested for their ability to predict fat mass, logarithm of fat mass, or a condition index (CI) incorporating fat mass. Equations generated to predict fat mass and the logarithm of fat mass accounted for more than 69% of the variation in these dependent variables. Log transformations of body mass, wing length, and total length explained at least 60% of the variation in CI. All models performed better on an independent data set. Mean prediction error was minimal (≤8% of measured variables) and negative for all models. Regression models apply to live and dead pintails and thus represent tools that have utility in a wide variety of studies on pintail condition.     

Scatter-hoarding behavior of deer mice ( Peromyscus maniculatus )

Deer mice ( Peromyscus maniculatus ) are known to larder hoard food, but their scatter-hoarding behavior is poorly documented. Eleven deer mice were each presented with 150 Jeffrey pine ( Pinus jeffreyi ) seeds in 10 γ 10- m enclosures in Jeffrey pine forests on the east slope of the Sierra Nevada. Subjects made a mean ± 1 s of 31.2 ± 30.0 caches per trial. Caches were shallow (most 2-12 mm deep) and usually contained only 1 or 2 seeds. Most caches were made at the edge of antelope bitterbrush ( Purshia tridentata ) shrubs in mineral soil or in thin layers of plant litter. These results suggest that deer mice might make a significant contribution to the dispersal of Jeffrey pine.     

Ecological classification and monitoring model for the Wyoming big sagebrush shrubsteppe habitat type of northeastern Wyoming

The purposes of this study were to develop a multivariate statistical model related to plant succession, to classify by seral stage, and to monitor succession in Wyoming big sagebrush shrubsteppe habitat ( Artemisia tridentata ssp. wyomingensis / Agropyron smithii–Bouteloua gracilis ) in Thunder Basin National Grassland, Wyoming. This model can be used by range and wildlife managers to evaluate management alternatives by assessing changes in plant species cover and composition within and between seral stages. Four ecological seral stages that represent early to late succession were quantitatively identified with an estimated 92% accuracy. Three key plant species provided the necessary information to define seral stages and monitor trends. Percent canopy cover and percent frequency (used to calculate index values: % canopy cover × % frequency of occurrence) of Wyoming big sagebrush ( Artemisia tridentata ssp. wyomingensis ), western wheatgrass ( Agropyron smithii ), and blue grama ( Bouteloua gracilis ) are the only field measurements required for this model.     

Food habits of young-of-year largemouth bass in Lake Mead and Lake Mohave, Arizona-Nevada

Young-of-year largemouth bass from lakes Mead and Mohave fed upon crustacean zooplankton, insects (primarily chironomids), and fish. Largemouth bass smaller than 32 mm TL fed extensively upon zooplankton. In Lake Mead, transition to an insect-dominated diet occurred at 32 mm TL; transition to an insect-fish—dominated diet did not occur in Lake Mohave until a length of 56 mm was reached. Largemouth bass from Lake Mohave consumed significantly more zooplankton than did those from Lake Mead, but largemouth bass from Lake Mead consumed significantly more insects. Fish were most common in the diet of young-of-year largemouth bass larger than 52 mm TL.