Distributional changes and population status of amphibians in the eastern Mojave Desert

Several amphibian species historically inhabited sparsely distributed wetlands in the Mojave Desert of western North America, habitats that have been dramatically altered or eliminated as a result of human activities. The population status and distributional changes of amphibians were investigated over a 20,000-km 2 area in the eastern Mojave Desert in 2 ways. For upland sites (i.e., sites outside of major valleys and river floodplains), where wetland habitat is almost exclusively springs, encounter surveys were conducted at 128 sites in 1997-1999, and results were compared to historical (pre-1970) locality records. For lowland sites (i.e., sites within major valleys and river floodplains), locality records and field surveys in 1995-2004 were reviewed to detect changes in distribution over time. Amphibians were found at 79% of upland sites. By far the most common species was the red-spotted toad ( Bufo punctatus , 73% of sites), followed by the Pacific chorus frog ( Pseudacris regilla ), Woodhouse's toad ( B. woodhousii ), relict leopard frog ( Rana onca ), and the introduced American bullfrog ( R. catesbeiana ). Taxa observed or collected in the lowlands since 1990 were Woodhouse's toad, Pacific chorus frog, American bullfrog, and the introduced tiger salamander ( Ambystoma tigrinum ). Four taxa (Vegas Valley leopard frog [ Rana sp.], Arizona toad [ B. microscaphus ], Great Plains toad [ B. cognatus ], and Great Basin spadefoot [ Spea intermontana ]) had historical records but no evidence of occurrence in the study area within the past 5 decades. The amphibian fauna of the study area has changed dramatically in the past century, primarily at lowland sites where habitat loss and modification have been extreme. Striking changes are the nearly complete replacement of native leopard frogs (i.e., Vegas Valley and relict leopard frogs) with the introduced bullfrog, and the complete replacement of the Arizona toad in Las Vegas Valley with Woodhouse's toad or hybrids with predominantly Woodhouse's traits. In contrast, the distributions of 2 species characteristic of upland springs, red-spotted toad and Pacific chorus frog, appear to have changed little from their historical distributions, despite habitat modification at many sites.     

Experimental manipulations of fertile islands and nurse plant effects in the Mojave Desert, USA

In a mixed desert shrub community we removed and added shrub canopies to examine above- and belowground influences of 3 species of shrubs on islands of soil fertility and the survival of transplanted Ambrosia dumosa seedlings. Soils sampled under shrubs in the wet season had higher pH, water content, organic matter, and both total and mineralizable nitrogen than soils in adjacent open areas, confirming a widely established pattern in arid lands. However, we also found species differences in soil parameters. Soils under Coleogyne ramosissima had highest pH, soils under A. dumosa had highest water content and nitrogen mineralization rates, and soils under Larrea tridentata had lowest water content. Soils sampled under shrubs in the dry season, 7 months after experimental shrub removal, maintained higher organic matter and total and mineralizable nitrogen content than adjacent open soils, but pH and water were altered by shrub manipulations. Species differences persisted only in soil water levels ( A. dumosa soils were driest). Over a 1-year period, transplanted A. dumosa seedlings had highest survivorship in shrub removal and open treatments and died most rapidly under control shrubs of all 3 species, suggesting that shrubs had a strong negative effect on seedling survival, even in the presence of higher organic matter, nutrients, and (initially) higher water content of fertile islands. Our results suggest that nurse plants and islands of soil fertility have the potential to facilitate growth of other species by nutrient additions, but that the net effect of nurse plants can be negative due to shading and/or root competition.     

Competition Between Adult and Seedling Shrubs of Ambrosia dumosa in the Mojave Desert, Nevada

Seeds of the perennial shrub Ambrosia dumosa germinated in abundance following 11 days of rain during August 1983 at a study site in the northern Mojave Desert. Seedling establishment, growth, and reproduction were observed in natural vegetation and in an area that had been previously cleared of vegetation. For 5,527 A. dumosa seedlings, percent survival in April 1986 averaged 3% in the undisturbed vegetation and 58% in the denuded area. Seedlings occupying the cleared area had grown to sizes up to 0. 1 m 3 m by October 1984; some produced flowers and fruit in the spring of 1985. Surviving seedlings in the undisturbed vegetation were all smaller than 0.001 m 3 and did not reproduce. These pronounced differences in growth, survival, and reproduction associated with the presence or absence of adult shrubs demonstrated an intense competition that is incompatible with indications of mild competition from nearest-neighbor analyses. I therefore hypothesize that competition for water occurred, not by competition for water in two dimensions but by rapid use of a common resource, as if several people were drinking with straws from a common cup. This temporal mechanism would strongly favor adults over seedlings.     

Age and population structure of Joshua trees ( Yucca brevifolia ) in the northwestern Mojave Desert

Many desert perennials are long-lived, but there are few data on ages or population structures of desert plants. We used 2 methods to estimate ages of a population of Yucca brevifolia (Joshua tree) in southwestern Utah from a 14-year census of plant sizes. Plant height at the 1st census ranged from 0.08 m to 6.0 m, and trees grew in height at a mean rate of 3.75 cm ? yr -1 . Plants also increased slowly in basal diameter (0.142 cm ? yr -1 ) and branch length (0.024 m ? yr -1 ), but basal diameter varied greatly from year to year, with many plants decreasing in diameter between sequential censuses. Forms of a nonlinear growth equation (the Richards function) did not fit the data on growth in height, but a simple linear relationship fit the data well. Using height as a linear predictor of age, we estimated that ages of a sample of 69 Joshua trees ranged from 300 years old, with 75% of the trees between 20 and 100 years and 11% over 150 years old. These data support the assumption that Joshua trees are indeed long-lived.     

Plant community patterns in unburned and burned blackbrush ( Coleogne ramosissima Torr.) shrublands in the Mojave Desert

The blackbrush vegetation type is dominated by Coleogyne ramossisima , which is thought to preclude the coexistence of many other plant species. Fire can remove blackbrush cover and possibly increase plant species richness and evenness. Fire also may increase the frequency and cover of alien annual grasses, thereby intensifying landscape flammability. We tested these predictions in unburned and burned (6-14 years postfire) blackbrush at 3 sites spanning the range of this vegetation type in the Mojave Desert. Species richness in unburned blackbrush was similar to published values for vegetation types in western North America, bur richness varied significantly among the 3 sites and 4 spatial scales (1, 10, 100, and 1000 m 2 ). Richness values declined in order from annual forbs, woody perennials, herbaceous perennials, annual grasses, cacti, to perennial grasses. Fire reduced Coleogyne cover, thus boosting species evenness. In contrast, species richness decreased after burning, although the results varied among spatial scales. Total cover was unaffected by fire because cover of wood perennials decreased, while cover of annual forbs, annual grasses, herbaceous perennials, and perennial grasses increased. Native species richness and cover decreased, whereas alien richness and cover increased after burning especially where the alien forb Erodium cicutarium was present. Fire had no effect on frequency and variable effects on cover of alien annual grasses. These results indicate that in blackbrush species richness can vary among sites and local spatial scales, and effects of fires can vary among plant life-forms and between natives and aliens.     

Influence of grassland type, nest type, and shrub encroachment on predation of artificial nests in Chihuahuan Desert grasslands

Nest predation on artificial nests was examined in relation to nest type, grassland type, and shrub encroachment in Chihuahuan Desert grasslands in southern New Mexico. Open-cup ground, open-cup shrub, and spherical shrub nests ( n = 210), mimicking Eastern Meadowlarks ( Sturnella magna ), Black-throated Sparrows ( Amphispiza bilineata ), and Cactus Wrens ( Campylorhynchus brunneicapillus ), were placed in 10 grasslands of tobosa ( Pleuraphis mutica ) and black grama ( Bouteloua eripoda ) with low and heavy levels of mesquite encroachment. Nest predation varied among nest types, grassland types, and shrub encroachment, with highest levels of predation occurring on open-cup shrub nests in tobosa grasslands with heavy shrub encroachment. We detected a significant interaction between nest type and shrub encroachment, but not between grassland type and nest type or grassland type and shrub encroachment. Combined predation rates from the 3 nest types were positively associated with shrub density. The encroachment of shrubs into desert grasslands may act as a corridor for a diversity of species historically not associated with desert grasslands to occupy or move through a patch, increasing vulnerability to nest predation.     

Ecological impacts of seed harvester ants on soil attributes in a Larrea -dominated shrubland

The influence of seed harvester ant ( Pogonomyrmex rugosus ) colonies on soil properties and soil surface and moisture characteristics was investigated through comparison of adjacent, nonnest (reference, 4 m beyond ant colony) areas in Las Vegas, Nevada. Effects of ant colonies on both terrace and slope sites were investigated. Soil moisture content and soil bulk density in a creosote bush ( Larrea tridentata )--dominated shrubland were significantly lower, while soil temperature, soil organic matter, and percent pore space were significantly higher in soils with ant nests relative to adjacent reference soils. Soil pH and texture did not differ significantly between nest and reference soils. Among soil surface characteristics, percent bare soil and rock (gravel, cobble, and boulder) cover were not significantly different between nest and reference soils. In evaluating soil moisture characteristics, soils with ant nests had a significantly higher water infiltrability and greater depth of water penetration, but a significantly lower area of water spread (surface-water runoff) at both terrace and slope sites. Between the 2 geomorphic surfaces, water infiltrability and depth of water penetration were significantly greater at the terrace than at the slope. Water-borne soil movement (fluvial erosion) was significantly greater at the slope than terrace but did not differ significantly between nest and reference soils. The presence of active P. rugosus colonies in the L. tridentata -dominated shrubland altered certain soil properties and appeared to have a protective influence on the soil by fostering more infiltration and less runoff of surface water in southern Nevada.     

Observations on the prey and nests of seven species of Cerceris (Hymenoptera: Sphecidae)

Cerceris species are remarkably constant in their prey preferences. Records are presented from diverse localities that confirm prey constancy in five species. An apparent exception is noted in the case of C. crotonella Viereck & Cockerell. A mixed aggregation of C. fumipennis Say and C. californica Cresson is reported, both preying upon Buprestidae and using some of the same species. Nest and prey of C. conifrons Mickel are reported for the first time.     

Grasshopper diversity and abundance in relation to elevation and vegetation from a snapshot in Mediterranean Anatolia: role of latitudinal position in altitudinal differences

Previously described patterns of altitudinal differences in species diversity and abundance still need to be tested in respect of generality across lineages and regions. Grasshopper diversity and abundance of an altitudinal transect in the eastern Mediterranean were studied to test the generality of these patterns. To identify the reasons underlying altitudinal differences, vegetation of the study area was studied. Our data show that species diversity and abundance are highest at middle altitudes and lower at high and low altitudes for grasshoppers. This pattern is consistent with that found in many arthropod groups, but it is not consistent with the pattern reported for Orthoptera in previous studies. A cluster analysis based on the grasshopper diversity and abundance identified three distinct altitudinal zones. Possible reasons for these distinct zones were the altitudinal differences in plant composition, the precipitous nature near the summits, urbanization and grazing livestock, and the latitudinal position of the study area.     

Influence of water size and type on bat captures in the lower Sonoran Desert

We compared bat use by mist-netting at 4 different types of wildlife water developments in southwestern Arizona during summer 2000 and 2001. Scaling our results by netting effort, we caught bats more frequently and observed higher species diversity at tinajas (modified natural rock pools) with larger open-water area compared with ""guzzler"" type water developments that had less open water and more obstacles to bat flight. We caught the fewest bats at guzzlers with buried concrete vault drinkers, which impede bat access and have the smallest areas of open water. Water development designs that minimize evaporative water loss by reducing the amount of open water apparently reduce use by bats in this area.     

The pre-overwintering nests and the immature stages of the hornet Vespa fumida van der Vecht (Hymenoptera: Vespidae)

The pre-overwintering nest structure and the immature stages of the hornet Vespa fumida van der Vecht are for the first time reported. All three adult forms (queen, worker and drone) are briefly described. The eggs have many micropyles concentrated at the larger end of the egg. The mature larvae can be identified by having the ecdysial sulcus obliterated ventrally; the parietal band distinctly margined ventrally on the outer side; the palate with a median patch and a pair of dorsal patches; the collar processes of the spiracle long and thick, with many branches over almost all the surface. Morphology and distribution of the different types of sensilla (setae, conical papillae, campaniform sensilla, basiconic sensilla, etc.) and the spicules are illustrated in detail. Close relationship between the Vespa affinis-group and V. fumida previously suggested by adult morphology is briefly discussed in terms of the morphology of the mature larvae.     

Effects of land clearing on bordering winter annual populations in the Mohave Desert

Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Construction of a 10-MWe solar thermal power plant in Daggett, California, involved clearing and leveling 53 ha of desert land. Transient offsite effects of this construction were apparent as a reduced density of annual plants within 100 m downwind of the edge of the cleared area. Schismus arabicus populations recovered within four years, but Erodium cicutarium populations did not. The effects appeared to be related more to an interaction of seed-dispersal mechanisms with the large, open space than to the obvious sand movement and deposition associated with the clearing operations.     

Occurrence and habitat use of passage neotropical migrants in the Sonoran Desert

Little is known about stopover habitat use by neotropical migratory birds in the deserts of North America. We determined distribution, abundance, and habitat associations of neotropical migrants during spring migration in the Sonoran Desert of southwestern Arizona along large washes that supported xeroriparian scrub vegetation. We detected 91 bird species during surveys, 50 (52%) of which were passage neotropical migrants. Although xeroriparian scrub covered less than 55% of the area surveyed, 97% of all detections of passage migrants were from this vegetation type. By calculating habitat breadth for each species, we classified 87% of passage migrants as xeroriparian specialists. Richness of passage migrants was strongly associated with the presence of overstory (> 2.5 m) mesquite and paloverde. The highest species richness of breeding neotropical migrants was associated with width of the xeroriparian corridor. Habitat characteristics we have shown to be important to neotropical migrants can be preserved and managed by protecting xeroriparian areas, particularly those supporting mature (> 2.5 m) paloverde, mesquite, desert willow, and catclaw acacia trees. Additionally, xeroriparian scrub within the creosote-bursage vegetation type may be particularly important to passage neotropical migrants.     

Breeding movements and reproductive activities of porcupine in the Great Basin Desert

I assessed movements of North American porcupines ( Erethizon dorsatum ) in the Great Basin of northwestern Nevada in relation to reproductive activities during the late summer and fall periods of 1991 and 1992. Porcupines exhibit a mate-defense polygynous mating system and I hypothesized that (1) competitively dominant males would have larger home ranges than both subordinate males and adult females, and (2) variation in home range size among adult male porcupines would be positively correlated with reproductive success. Results indicated that dominant male porcupines ranged over larger areas (average 95% minimum convex polygon home range = 20.7 ha) than subordinate males (average 95% MCP home range = 2.9 ha) and adult females (average 95% MCP home range = 8.2 ha). Analyses of movements in relation to body size and energetic requirements revealed that home ranges of dominant male porcupines were larger than predicted based on body size (approximately 10.2 ha). Breeding period home ranges of dominant male porcupines encompassed portions of the home ranges of 3 to 10 adult females, and indices of reproductive success based on observations of mate-guarding behaviors suggested a strong positive relationship between home range sizes of male porcupines and mating success. Together these data suggested that larger home ranges among dominant males were related to increased mating opportunities and not increased metabolic requirements associated with larger male body sizes. In the study area, however, female porcupines congregated around small, patchily distributed riparian areas, and dominant males with relatively small home ranges encompassing riparian areas may have gained mating access to multiple females. Finally, analyses of overlap among core home ranges (60% MCP) of adult male and adult female porcupines suggested that both sexes maintained relatively exclusive core home range areas, with males exhibiting significantly less range overlap with other males ( ￣x = 9.4%) than females with other females ( ￣x = 27.1%). It is possible that the small, patchily distributed riparian areas in this desertlike area were such a limited resource that females were unable to maintain exclusive use of their home range areas.     

Social facilitation and food partitioning in the queenless ant Dinoponera quadriceps (Hymenoptera: Formicidae)

Social facilitation occurs when an animal is more likely to behave in a certain way in response to other animals engaged in the same behaviour. For example, an individual returning to the nest with food stimulates other ants to leave and to forage. In the present study we demonstrate the existence of new facets in the colony organization of Dinoponera quadriceps: a positive feedback between the incoming food and the activation of new foragers, and the occurrence of incipient task partitioning during the food sharing. Lower-ranked workers located inside the nest process protein resources and higher-ranked workers handle smaller pieces and distribute them to the larvae. In conclusion, D. quadriceps has a decentralized pattern of task allocation with a double regulatory mechanism, which can be considered a sophisticated aspect of division of labour in ponerine ants.     

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.     

A taxonomic and zoogeographical census of the extant ant taxa (Hymenoptera: Formicidae)

The numbers of extant ant taxa in the world are analysed taxonomically and zoogeographically. A table detailing numbers of subfamilies, tribes and genera, and the numbers of species they contain, and one analysing the number of species per genus per zoogeographical region, are presented. Subfamilies are analysed by number and percentage of genera and species; the most speciose genera are isolated and listed in terms of absolute size and speciosity per subfamily. Tables detailing total numbers of genera and species per subfamily per region, and endemic genera per subfamily per region are given, and the endemicity and speciosity of genera are tabulated on a regional basis.