Prey choices and foraging efficiency of recently fledged California Gulls at Mono Lake, California

We studied the foraging biology of recently fledged California Gulls ( Larus californicus ) at Mono Lake during August-September 1991. We made behavioral observations to collect information on the relative proportions of different prey types in the diet of these birds and took plankton tows to determine the relative abundance of each prey in the water column. These data show that alkali flies ( Ephydra hians ) were the primary constituent of the diet and that they were eaten at a much higher rate than one would expect based on their abundance. We also determined the number of feeding attempts and successful captures made during each behavioral observation. From these, we calculated the bird's feeding efficiencies on emergent adult alkali flies and on all other prey types combined. We found that foraging efficiencies on emergent flies were very high and significantly greater than those obtained on other prey types. These results suggest that flies were actively sought in preference to the alternative prey type, brine shrimp ( Artemia monica ), presumably because they are easier to capture and of greater nutritional value.     

Terrestrial vertebrates of the Mono Lake islands, California

We compared vertebrate populations between the two major islands (paoha and Negit) in Mono Lake, California and the adjacent mainland to further elucidate the mechanisms underlying island colonization. Deer mice ( Peromyscus maniculatus ) and montane voles ( Microtus montanus ) were captured on Paoha, but only deer mice were captured on Negit. In contrast, eight species of rodents were captured on the mainland. Overall rodent abundance on Paoha and the mainland was similar, but on Negit it was about three times greater than on Paoha or the mainland. Adult deer mice from Paoha were significantly ( P Canis latrans ) and one or two species of lagomorphs were observed on the islands and the mainland. No amphibians or reptiles were found on the islands; both occurred in low numbers on the mainland. Rafting and human transport are probable means of colonization for mice and voles. The occurrence of coyotes on the islands may have modified historic predator-prey relationships, and thus the population of rodents and lagomorphs.     

Diatom flora of Cowboy Hot Spring, Mono County, California

The diatom flora of Cowboy Hot Spring, Mono County, California, was studied. Two habitats, one at 37C and one at 41C, were examined. Fifty-six taxa were identified from our samples. These taxa were mostly broadly distributed forms, and no endemic species were encountered. The dominant taxon was Nitzschia frustulum, followed by Achnanthes gibberula, Achnanthes exigua, Nitzschia hantzschiana , and Navicula cincta .     

Zonation patterns in the vascular plant communities of Benton Hot Springs, Mono County, California

Vascular plant communities surrounding Benton Hot Springs, Mono County, California, were studied. The springs complex is comprised of two thermal springs, a thermal stream, and a cooling pond. Water temperatures varied from 57 C in one hot spring to 45 C at the cooling pond. The vegetation showed concentric zones about the springs and cooling pond and parallel zones beside the stream. Each zone demonstrated its own dominant plant species with some species being present in two or more zones. A total of six zones were identified plus an algal mat on the springs themselves. Soil factor patterns varied from spring to desert as did vegetational parameters. Soil moisture appeared responsible for most of the patterns observed.     

Invasion of big sagebrush ( Artemisia tridentata ) by white fir ( Abies concolor ) on the southeastern slopes of the Warner Mountains, California

White fir ( Abies concolor ) appears to be invading vegetation dominated by big sagebrush ( Artemisia tridentata ) on the southeastern slopes of the Warner Mountains of extreme northeastern California. The time of initial tree establishment within the shrubs was determined by increment borings. Possible causes of the invasion involving specific climatic conditions, fire history, and grazing use of the area during years of the establishment were explored. Heavy grazing by domestic livestock, particularly sheep, appears responsible for altering the sagebrush - grass vegetation and allowing tree invasion.     

Observations on the ecology and trophic status of Lake Tahoe (Nevada and California, USA) based on the algae from three independent surveys (1965-1985)

Numerous physical, chemical, and biological criteria evidently confirm that Lake Tahoe is oligotrophic. However, detailed examination of the ecology and trophic status status of algae (mostly diatoms) from Lake Tahoe taken from three independent, long-term sampling programs aided in interpretation of plankton and periphyton algal communities by spectral analysis (supported by computerized data synthesis) and "ultra-oligotraphic" lakes over the world from which future studies may reveal algal communities that may be described as more mesotrophic and/or eutrophic than oligotrophic. Lake Tahoe probably is not as oligotrophic as is generally believed, and the indicator algae in it are not as accurate as is generally believed.     

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.     

Sex ratios of the white-tailed antelope ground squirrel (Ammospermophilus leucurus), Indian Wells Valley, San Bernardino County, California

We studied the white-tailed antelope ground squirrel during spring and summer 2006 to determine young-of-the-year and adult sex ratios in the Indian Wells Valley, San Bernardino County, California. We calculated a young-of-the-year sex ratio of 1.45:1 (female to male), whereas the adult sex ratio was approximately 1:1. Our young-ofthe-year sex ratio was greater than the 1.1:1 (female to male) natal sex ratio previously reported. Differences between young-of-the-year and adult sex ratios may represent low female young-of-the-year survivorship in the Indian Wells Valley.     

Density, biomass, and diversity of grasshoppers (Orthoptera: Acrididae) in a California native grassland

A native California perennial grassland was sampled for grasshopper populations. The grassland is managed for the preservation of the native perennial bunchgrass, Nassella pulchra Hitch. Grasshopper density, biomass, diversity, and richness were measured from July 1993 to October 1994. Average density of all grasshoppers was 2.30 hoppers/m 2 (0.66 s ) for 1994 (June through August). Overall forage consumed for 1994 was 140 kg/ha, suggesting that grasshopper populations exist at economically damaging levels. Grasshoppers do not appear in the grasslands until late spring, after annual grasses have set seed. Biomass of grasshoppers peaks in July when adults are predominant. Both grasshopper density and biomass were higher in 1993 than in 1994, and a total of 5 species were found throughout the study. Melanoplus sanguinipes Fabricus dominated the acridid communities and accounted for more than 95% of the individuals.     

Riffle beetles (Coleoptera: Elmidae) of Death Valley National Monument, California

Three species of Elmidae occur in Death Valley National Monument: Stenelmis calida is in three springs in the Ash Meadows area; Microcylloepus formicvideus is only in Travertine Springs; and Microcylloepus similis is in several springs throughout Death Valley and Ash Meadows. Only permanent springs support elmids. Considerable morphological variation occurs in the disjunct populations of M. similis . The evolution of elmids in Death Valley National Monument is equivalent to that of the local pupfish ( Cyprinodon spp.).     

New species of Mentzelia (Loasaceae) from Grand County, Utah

A new species, Mentzelia (Section Bartonia ) shultziorum , of the Loasaceae (Mentzelioideae) is described. A close relationship with M. multicaulis (Osterh.) Darl. and M. argillosa Darl. is suggested based on the morphology of the flowers, leaves, and seeds.     

New species of Astragalus (Leguminosae) from Mesa County, Colorado

Named and described is Astragalus debequaeus Welsh from Mesa County, Colorado.         

Calileuctra , a new genus, and two new species of stoneflies from California (Plecoptera: Leuctridae)

Calileuctra is proposed as new genus in the family Leuctridae, with Calileuctra ephemera designated as the type species. All stages of Calileuctra ephemera are descpribed. Calileuctra dobryi is described in the male and female stages. Both species inhabit Mediterranean climatic region of California. A phylogenetic analysis of the genera in the family Leuctridae is given, which places Calileuctra near the genus of Perlomyia .     

Diet and food-niche breadth of Burrowing Owls ( Athene cunicularia ) in the Imperial Valley, California

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

Hesperoperla hoguei, a new species of stonefly from California (Plecoptera: Perlidae)

A new species of Hesperoperla is named from northern California. The adult male and female, nymph, and egg are described and figured. Hesperoperla hoguei adds a second species to this previously monotypic genus.     

Notes on some larval and pupal chironomids (Diptera) from Lake Kariba,Rhodesia

Summary

The effects of hydrolysable tannin and condensed tannin on the feeding of Schistocerca gregaria and Locusta migratoria are described. An attempt is made to explain the different effects of tannins in the presence of different nutrients. The ecological significance of these findings is discussed.     

Littoral heterogeneity and diel behavior of white bass ( Morone chrysops ) and carp ( Cyprinus carpio ) in Utah Lake, Utah

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;} Diel activity and association patterns of white bass ( Morone chrysops ) and carp ( Cyprinus carpio ) in Utah Lake, Utah, were studied over four 24-hr periods during August 1980. Fish were concurrently sampled from two adjacent littoral habitats. Significant differences existed in diel activity patterns in two of three size classes of white bass and in diel association patterns of white bass and carp between the two habitat areas. Differences in habitat structure, and in biological activity between the habitat types, are implicated as the primary determinants of overall diel activity of fish in these littoral areas.        

Sasquaperla Hoopa , a new stonefly genus and species from northern California (Plecoptera: Chloroperlidae)

Sasquaperla hoopa , a new genus and species of Chloroperlidae, is described from adults and preemergent nymphs collected in the Coast Range of northern California. Males are characterized by the epiproct reduced to a small, tablike structure bearing stiff hairs in a narrow band along the posterior margin. Females are similar to those of Sweltsa , but the nymphs bear several erect bristles lateral to depressed hair patches on the mesosternum. Modified keys are presented for adults and nymphs.