Desert rodents reduce seedling recruitment of Salsola paulsenii

Heteromyid rodents in the deserts of North America have been shown to harvest large quantities of seeds of both native and introduced plants from soil seed banks, but rarely has the impact of this seed removal been demonstrated experimentally. I used a series of fenced plots (some of which excluded rodents) to demonstrate that heteromyids at a western Nevada study site can measurably reduce seed banks and subsequent seedling establishment of Salsola paulsenii , an introduced invasive weed that has become a significant problem over much of the desert Southwest. The frequency of S. paulsenii seedlings in both 2004 and 2005 was significantly greater around the interior perimeters of plots that permitted access by rodents than in plots that excluded rodents. Density of S. paulsenii seedlings was significantly greater inside than outside rodent exclusion plots, but there was no such difference in seedling density inside versus outside plots that permitted rodent access. Salsola paulsenii has such a conspicuous presence in many desert environments that the effect of rodents in reducing its abundance may not be visually apparent; however, rodents may still ameliorate competitive effects of this weed on coexisting plants. Heteromyid rodents disperse seeds through caching, and they also consume them. Caching may enhance establishment of native plant seedlings, but is unlikely to benefit exotics such as S. paulsenii .     

Controls on radial growth of mountain big sagebrush and implications for climate change

Mountain big sagebrush ( Artemisia tridentata Nutt. ssp. vaseyana ) covers large areas in arid regions of western North America. Climate-change models predict a decrease in the range of sagebrush, but few studies have examined details of predicted changes on sagebrush growth and the potential impacts of these changes on the community. We analyzed effects of temperature, precipitation, and snow depth on sagebrush annual ring width for 1969 to 2007 in the Gunnison Basin of Colorado. Temperature at all times of year except winter had negative correlations with ring widths; summer temperature had the strongest negative relationship. Ring widths correlated positively with precipitation in various seasons except summer; winter precipitation had the strongest relationship with growth. Maximum snow depth also correlated positively and strongly with ring width. Multiple regressions showed that summer temperature and either winter precipitation or maximum snow depth, which recharges deeper soil horizons, are both important in controlling growth. Overall, water stress and perhaps especially maximum snow depth appear to limit growth of this species. With predicted increases in temperature and probable reduced snow depth, sagebrush growth rates are likely to decrease. If so, sagebrush populations and cover may decline, which may have substantial effects on community composition and carbon balance.     

Larger ectoparasites of the Idaho ground squirrel ( Spermophilus brunneus )

We sampled both subspecies of the Idaho ground squirrel ( Spermophilus brunneus ) to document the larger ectoparasites of this rare endemic. S. b. brunneus was host (+ = new host record, ? = new Idaho record) to 4 flea species ( Neopsylla inopina + , Oropsylla idahoensis + , O. tuberculata , and Thrassis pandorae +), 1 tick ( Ixodes sculptus +), and an eyeworm (Nematoda: Rhabditis orbitalis ? + , also 1st records from Seiuridae); S. b. endemicus was host to a louse species ( Neohaematopinus laeviusculus +), 5 flea taxa ( Rhadinopsylla sp. + , O. t. tuberculata, Thrassis f. francisi + , T. f. barnest + , and T. f. rockwoodi ), and a mite ( Androlaelaps fahrenholzi +). Spermophilus brunneus had fewer known ectoparasite species than other congeners. Although all of their parasites had many other hosts, S. b. endemicus and S. b. brunneus shared only a single parasite species in common, whereas all but one of their ectoparasites also occurred on the closely related Townsend's ground squirrel ( S. townsendii ). The proportion of parasitized individuals and the parasite loads per individual were significantly lower in S. b. brunneus , which lives in small, isolated populations, than in S. b. endemicus , which has larger, less fragmented populations, suggesting a relationship between host population structure, parasite loads, and parasite species diversity. All but one of the flea species have been linked to plague transmission.     

Den and relocation site characteristics and home ranges of Peromyscus truei in the White Mountains of California

We used ratio telemetry to describe nighttime movements and daytime den sites of pinyon mice ( Peromyscus truei ) in the White Mountains of California, 1991-1993. Characteristics of nighttime relocations and den sites for mice concurred with previously reported habitat-use information for the species and supported the claim that pinyon mice use multiple daytime sites. However, males and females were associated with different habitat characteristics at den sites, indicating differential microhabitat selection by the sexes, perhaps related to reproductive constraints on females. Pinyon mice also exhibited high variability in den site habitat use in the summer, but low variability in the fall and winter. The dens of male mice were farther apart than those of females, and home range areas averaged 2.9 ha ( s = 4.27 ha) for 8 males , and 0.8 ha ( s = 0.76 ha) for 7 females (overall ￣ x = 1.7 + 2.97 ha). These areas were larger than those reported for other species of Peromyscus . The combined effects of drought and reduced food availability may have contributed to the larger areas used.     

Microhabitat selection in the sand recluse spider (Sicarius thomisoides): the effect of rock size and temperature

In spiders, temperature is considered an important environmental variable for microhabitat selection. In this study, we evaluated the effect of temperature and rock size on the presence of the sand recluse spider Sicarius thomisoides and the degree of selectivity in different locations. This species is a large spider that lives under rocks in desert and semi-desert climates and is particularly active during the summer. In Chile, these spiders can be found at both coastal and inland locations under different thermal conditions, where usually the temperatures are lower near the coast. If large-scale climatic conditions are important for this species, they may be expected to select lower rock temperatures on the coast than at inland locations. In addition, we would expect that the spiders would choose larger rocks in inland compared to coast locations, which reduce the effect of high temperatures. We found that the probability of finding individuals of this species increased according to rock temperature and rock size in the field. Our results suggest that S. thomisoides prefers larger and warmer rocks to shelter under during the day, this selectivity being similar at both coastal and inland locations. Thus, this species tends to select rocks with the same thermal and structural conditions, independent of the climatic conditions.     

Bristlecone pine and Clark's Nutcracker: probable interaction in the White Mountains, California

Many bristlecone pines in the White Mountains, California, are members of multistem clumps. We propose that these clumps have arisen by multiple germinations from seed caches of Clark’s Nutcracker, as occurs in several other pine species. The commonness of nutcrackers and their caching of singleleaf pinyon seeds in the study area provide supporting evidence. Other vertebrates appear unlikely to be responsible for the stem clumps. Seed burial may be required to establish regeneration on these adverse sites where bristlecone pine attains great longevity.        

Effect of Timing of Grazing on Soil-Surface Crytogamic Communities in a Great Basin Low-Shrub Desert: A Preliminary Report

Cover and species richness of vascular and cryptogamic components of the plant community were inventoried in experimental grazing paddocks at the USDA/FS Desert Range Experimental Station, Millard County, Utah. The grazing treatments considered have been applied continuously for over 50 years. The effects of heavy (ca 17 sheep days/acre) grazing treatment applied in two different seasons (early winter versus a split between early and late winter) differed significantly between seasons. Cryptogamic cover and cryptogamic species richness both showed larger decreases under early-late as opposed to early winter only grazing. Vascular plant cover (relative to controls) was also reduced by early-late winter grazing, but not to a significant degree. Late season grazing, likewise, had no significant effect on number of vascular species per transect.     

Population structure and ecological effects of the crayfish Pacifastacus leniusculus in Castle Lake, California

The recent appearance of the ""California crayfish,"" Pacifastacus leniusculus , in Castle Lake, California, and interest in its potential impacts on the lake ecosystem provided motivation for a study of the population structure and habitat use of this species and its effects on aquatic macrophytes. Mark-recapture studies indicated that the total number of adult (3 + yr or older) crayfish in the lake was ca 10,100 individuals, yielding an estimate of lakewide crayfish density in preferred crayfish habitats of 0.13 adults m -2 . Using mean body mass of individuals, we estimated that ambient biomass density was 5.9 g m -2 . Length-weight relationships determined for captured individuals were sex dependent, with males having greater body mass for a given carapace length. Length-frequency and weight-frequency diagrams indicated that P. leniusculus reaches larger sizes in Castle Lake than do populations of P. leniusculus in ultraoligotrophic Lake Tahoe. Population-wide, males were significantly larger in both carapace length and body mass than females. We also examined sex dependence of interhabitat differences in crayfish body size by comparing animals trapped in rocky areas with those from areas with macrophytes and soft sediments. No significant differences in overall body size were found between habitats, but a significant habitat-sex interaction term occurred because the sex-dependent size differences were more pronounced in sediment than in rocky areas. Exclosure and enclosure experiments indicated that crayfish had large but differential impacts on Castle Lake macrophyte species, as the abundance of two of the dominant species ( Chara sp., Potamogeton richardsonii ) declined in the presence of crayfish and, in one case, increased in exclosures. These effects occurred via both consumptive and nonconsumptive mechanisms. These studies indicate that and expanding population of P. leniusculus in Castle Lake may be producing sizable impacts on the littoral zone habitat.     

Winter site fidelity and body condition of three riparian songbird species following a fire

The effects of fire on nonbreeding songbird species in riparian habitat have not been studied. We compared body condition, within-year site fidelity, and between-year site fidelity of 3 songbird species ( Passerella iliaca , Fox Sparrow; Catharus guttatus , Hermit Thrush; and Regulus calendula , Ruby-crowned Kinglet) at 2 coastal riparian sites. Wildfire, which is rare in this habitat, had occurred at 1 of the sites before data collection. A significantly larger proportion of Passerella iliaca was recaptured in subsequent winters at the unburned site than at the burned site, but little difference was found between sites for Catharus guttatus or Regulus calendula . Body mass of all 3 species declined during winter at the burned site, but differences between sites were not significant. Similarly, body mass indices of new captures were lower at the burned site than the unburned site for all 3 species, but these differences were not significant. The within-year recapture rate for all 3 species combined declined at the burned site over the course of the study, possibly due to changes in vegetation structure caused by the fire. Overall, our data suggest that wintering songbirds were resilient to this disturbance, but that response to the post-fire environment differed among foraging guilds. Well-replicated studies that include pre-burn data are needed to evaluate the effects of this disturbance in riparian systems.     

Avian mortality due to power lines in the Canary Islands with special reference to the steppe-land birds

Biodiversity is being lost worldwide at an increased rate particularly as the result of human activities and infrastructure. Avian mortality through collision with power lines has been an important topic in animal ecology research, but studies of this kind have never been undertaken in the Canary Islands, a volcanic archipelago located near the northwest African coast that has important seabird colonies, several endemic bird species and endemic races of steppe-land birds of conservation concern. During two contrasting periods in 2008 (breeding vs post-breeding), a total of 366 km of power lines were surveyed on this archipelago covering the entire distributional range of the most important steppe-land bird species (i.e. 232 km, Fuerteventura; 134 km, Lanzarote). In all, 310 carcasses representing 23 families and 26 species were detected. We estimated with distance Sampling that 25.5% and 6.3% of individuals of the total population of Houbara bustards, Chlamydotis undulata fuertaventurae, and Eurasian stone curlews, Burhinus oedicnemus insularum, respectively, were killed in a year. We encourage the Canary Islands authorities (Consejería de Medio Ambiente del Gobierno de Canarias) to try to minimize the Houbara bustard collision rate, particularly in the northern plains of Lanzarote (i.e. Jables de Famara), as a means to reduce mortality of this emblematic species in this insular environment.     

Exclusion experiments with backwater invertebrate communities of the Green River, Utah

The role of biotic interactions in structuring freshwater invertebrate communities has been extensively studied but with mixed results. For example, fish effects on invertebrates are most pronounced in pelagic and soft-sediment benthic habitats that lack structural complexity, yet appear insignificant in benthic rubble habitats. Backwaters of the Green River, Utah, are shallow, structurally simple, quiet-water embayments adjacent to the river. These habitats form in middle to late summer and are colonized by benthic and epibenthic invertebrates that produce standing crops significantly higher than the river. Backwaters are also utilized by a large number of fish species. We used cages to determine if selective exclusion of backwater organisms could significantly change invertebrate community structure. Results showed that backwater invertebrate community components changed significantly in response to exclusion treatments. Two taxa (both predators), the chironomid genus Tanypus (Diptera: Chironomidae) and the corixid genus Trichocorixa (Hemiptera: Corixidae), increased in density in exclusion cages while cladocerans, immature copepods, the cyclopoid copepod Eucyclops speratus , and the chironomid genus Procladius all decreased in density. Diversity of adult copepods was reduced by exclusion treatments, though density of only a single species changed significantly.     

Necrophagous or predators? The role of Pheidole radoszkowskii Mayr (Hymenoptera: Formicidae) on Rattus norvegicus (Berkenhout) carcasses (Rodentia: Muridae)

This study aimed to identify the feeding habit of Pheidole radoszkowskii Mayr on Rattus norvegicus (Berkenhout) carcasses, as well as whether its presence limits the occurrence of flies. Pheidole radoszkowskii exhibited more necrophagous than predatory behaviour. Its abundance was inversely proportional to that of flies, confirming that this ant species may cause lesions in carcasses and its presence limits the occurrence of flies. This work clarifies the behaviour of an ant species often encountered on carcasses.     

Effects of elevation and genetic introgression on growth of Colorado River cutthroat trout

Inland populations of cutthroat trout have suffered dramatic declines and some subspecies are considered threatened or endangered. Understanding patterns of variation and factors that influence life history in populations is important for conservation and management. We determined effects of elevation, sex, and genetic introgression (with Yellowstone cutthroat trout, Oncorhynchus clarkii lewisi , and rainbow trout, Oncorhynchus mykiss ) on growth rates of Colorado River cutthroat trout ( Oncorhynchus clarkii pleuriticus ) in the Sheep Creek drainage in the Uinta Mountains of Utah. In this high-elevation system, native trout grew slowly and matured relatively late. Elevation, sex, and genetic introgression all had significant effects on growth rates. Growth rates were lower at higher elevations. Males were slightly larger than females, and cutthroat trout in locations that were more introgressed grew faster than those at nonintrogressed locations. Both abiotic effects and effects of introduced salmonids must be addressed in long-term management programs to ensure the sustainability of native trout populations.     

A mixed pollination system in Penstemon pseudospectabilis M. E. Jones (Scrophulariaceae)

A population of Penstemon pseudospectabilis M. E. Jones (Scrophulariaceae) on Cave Creek in Cochise County, Arizona, was used in an experimental test of reproductive fitness with three caging treatments: all flying pollinators excluded, hummingbirds excluded, and no exclusion. Twenty plants were chosen and three shoots on each used in the experiment. The flowers were 25.6 (s.d. = 1.5) mm long, the end diameter was 8.5 (s.d. = 1.0) mm, the tube opening was 6.5 (s.d. = 1.0) mm, and the greatest diameter, 75% distal from the receptacle, was 10.1 (s.d. = 0.8) mm (N= 59). Floral nectar contained 11.7% (s.d. = 2.9%) fructose, 13.8% (s.d. = 2.7%) glucose, and 74.5% (s.d. = 5.4%) sucrose (N = 74). There was some evidence, significant only for fructose, that nectar-sugar composition varies between morning and evening. Larger floral dimensions were correlated with lower sucrose and higher hexoses. Casual observation showed Xylocopa sp., small bees, flies, and hummingbirds to be visitors. There was no sign of nectar robbing. Five percent of flowers set seed with all pollen vectors excluded, 44% with hummingbirds excluded, and 63%with no exclusion. Seed set per fruit was 2 with all excluded, 23 with hummingbirds excluded, and 46 with no exclusion. Mean seed set on pollinated flowers was 60, with a range of 2 to 192. Multiple linear regression showed the fraction of fruit setting seed when hummingbirds were excluded to be related to larger flower diameters and shorter flowers. With no pollinator exclusion, fruits setting seed were related to larger diameters and nectar fructose. For seeds per fruit, multiple regression gave similar, but less clear, results. We conclude that P. pseudospectabilis is pollinated by both bees and hummingbirds, with other pollinators not to be excluded as possible contributors. We found no hard evidence of selective forces currently at work.     

Diet switching and food delivery by shrubsteppe passerines in response to an experimental reduction in food

We experimentally reduced the food base of nesting Brewer's Sparrows ( Spizella breweri ) and Sage Thrashers ( Oreoscoptes montanus ) in a shrubsteppe region of south central Idaho in 1989 and 1990. Frequency and mass of "birdfood" arthropods in pitfall, sweep net, and stickyboard samples were generally lower on sites treated with a broad-spectrum insecticide (malathion) than on untreated sites though the effect varied among taxa. In 1990 O. montanus switched nestling diets to prey taxa not affected by the treatment. Time between nestling food deliveries was greater for S. breweri on the treated than untreated site in 1989. In 1990 there were no between-site differences, but there was an increase in delivery time on the treated plot after treatment; this difference was within the range of delivery times recorded on the untreated plot. Malathion applications did reduce the food base, but plasticity in passerine behavior and emergence characteristics of some prey taxa ameliorated indirect effects of food reduction to birds.     

Competition for food and space in a heteromyid community in the Great Basin Desert

A series of removal experiments were performed on Dipodomys merriami, D. microps, and Perognathus longimembris to test for the importance of competition for food and microhabitats in a heteromyid community in the Great Basin Desert. Each of these species was removed singly to determine the short-term effects on the microhabitat preferences of the remaining species. We correctly predicted, based on differences in diet, that the removal of D. microps (a foliovore) would have no effect on D. merriami or P. longimembris (granivores). Using the dominance hierarchy theory, we correctly predicted that removal of a larger heteromyid, D. merriami, would have an effect on the microhabitat use of the smaller P. longimembris, but not vice versa. While our results offer strong evidence of competition for food and microhabitats, the short-term reactions were weak compared to the long-term reactions found in other studies of heteromyids.     

Conservation of European environments: The Spheciformes wasps as biodiversity indicators (Hymenoptera: Apoidea: Ampulicidae,Sphecidae and Crabronidae)

The aim of this work is to propose the use of the Spheciformes wasps (Hymenoptera: Apoidea: Ampulicidae, Sphecidae and Crabronidae) as indicators of European biodiversity. One advantage of studying this group of insects lies in the regulating effects that such wasps have on other insect populations. We discuss the applicability of seven criteria, taken from the literature, to use the Spheciformes wasps as an indicator group, with respect to which parameters this group offers guarantees of being good indicators of biodiversity, both for predicting the diversity of other groups of animals and for all the species of a given area.     

Livestock and vegetation responses to rotational grazing in short-grass steppe

There is a paucity of information concerning livestock and vegetation responses to rotational grazing in short-grass steppe. We compared effects between 1995 and 2003 of time-controlled, short-duration rotational grazing against season-long continuous grazing, at a moderate stocking rate (1.95 ha ? animal unit month –1 ), on livestock gains and on foliar and basal cover in short-grass steppe. Livestock average daily gains, grazing-season gains, and beef production did not differ between grazing systems. We observed no relationship between precipitation (annual or growing-season) and average daily gain. In contrast, both grazing-season gains and beef production exhibited a significant curvilinear response to both growing-season and annual precipitation. Basal and foliar cover of all plant functional groups (C 3 annual grasses, C 3 perennial grasses and grass-likes, C 4 perennial grasses, cactus, annual forbs, perennial forbs, and shrubs/subshrubs) did not differ between grazing systems. Litter and bare ground were also unaffected by grazing system, with litter increasing and bare ground decreasing over the duration of this experiment. Land managers in shortgrass steppe who are implementing rotational grazing at moderate stocking rates should not expect increased livestock gains or changes in basal and foliar cover of the plant community. Rotational grazing may be a useful management tool for achieving conservation goals through modifications of seasonality and intensity of use in paddocks within larger management units to accommodate spatial variability in vegetation and temporal variation in precipitation.