Spring denitrification rates in soils of four eastside Sierra Nevada plant communities

Denitrification rates in soils of four subalpine plant communities in the Sierra Nevada were determined by the acetylene blockage method. The study area included riparian, meadow, forest, and barren sites. Data were collected during dawn-to-dusk measurements in April 1987. Soil atmosphere samples were analyzed for N 2 O content using gas chromatography. Generally, temporal variability in denitrification rate within each plant community was insubstantial. Denitrification rate and soil temperature were found to be significantly correlated only in the riparian and barren sites. Of the four communities, the riparian site was found to have the lowest rate of denitrification overall. However, differences among sites in denitrification rate could not be conclusively attributed to variation in soil temperature, moisture, organic matter, total C and N, C:N ratio, NO 3 - N, or pH.     

Recovery and germinability of native seed fed to cattle

Using livestock as seed dispersal agents may be an effective method for increasing species diversity on degraded and previously seeded rangelands. We quantified seed passage and recovery rates, and post-passage germinability of Wyoming big sagebrush ( Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young), bottlebrush squirreltail ( Elymus elymoides [Raf.] Swezey), and gooseberry globemallow ( Sphaeralcea grossulariaefolia [H. & A.] Rydb.) by feeding Holstein heifers seeds of each species at 3 levels (15,000; 30,000; and 60,000 seeds) over a period of 3 weeks. One-kg fecal samples were collected 1, 2, 3, and 4 days after seed ingestion. Undamaged seeds were extracted from the samples and tested for germinability. Globemallow had the highest percentage of recovered, undamaged seed, followed by squirreltail and sagebrush. Globemallow and sagebrush seed passage was highest on Day 1, after which seed numbers dropped sharply. Squirreltail passage and recovery were more consistent through time, with higher seed recovery at lower seed feeding levels. Post-passage germinability was highest for squirreltail and globemallow on Day 1. Sagebrush germination was negligible. Differences in physical seed properties (size, shape, and seed coat) likely influenced interspecies variation in passage, recovery, and germinability. Globemallow and squirreltail seeds may be suited for livestock dispersal, but sagebrush seeds are not.     

How survival and food intake of tri-spine horseshoe crabs,Tachypleus tridentatus respond to thermal variation: implications for understanding its distribution limit

ABSTRACT

Temperature appears to have pervasive effects on larval development, feeding and movement patterns of tri-spine horseshoe crabs, Tachypleus tridentatus. To investigate how temperature determines their geographic distribution range, we examined the survival rate (SR), survival time (ST) and food intake of subadult T. tridentatus under different temperature levels in a seven-day experiment, followed by a three-day recovery to room temperature at 25°C. Significantly lower SR and ST of subadults were found at 40°C after the end of the seven-day experiment. Meanwhile, SR and ST of individuals at 0°C were negatively affected when the temperature was brought back to 25°C. Mean food intake of the subadults was statistically lower at 0–20°C and 35–40°C compared to that at 25°C and 30°C. After the subsequent three-day recovery to 25°C, only the individuals previously exposed to 15°C and 20°C had recovered to their normal level of feeding activities, but not the other treatment groups. These findings may provide preliminary data on how thermal tolerance determines the present distribution of T. tridentatus, which are found in large numbers around Beibu Gulf (annual temperature variation: 22–30°C), while considerably lower population densities are observed in the colder southern Sea of Japan and warmer seas of Southeast Asia.     

Untying a Gordian knot: the domestication and laboratory maintenance of a Gordian worm,Paragordius varius (Nematomorpha: Gordiida)

Twenty-one sand field crickets (Gryllus firmus) were infected with naturally collected cysts of the Gordian worm, Paragordius varius (Nematomorpha: Gordiida). The life cycle was completed by infecting laboratory-reared paratenic hosts with P. varius larvae. The life cycle has been maintained subsequently in the laboratory for numerous generations. This is the first time the life cycle of a member of the phylum Nematomorpha has been completed experimentally. Maturation within the definitive host took from 27 to 30 days post-exposure. The natural and laboratory life cycles of Paragordius varius vary in that a more easily maintainable paratenic host is used in the laboratory than is used in nature. The complete domesticated model life cycle is maintained easily and takes as few as 45 days. Data gathered from 46 laboratory-infected cricket hosts indicated that sex ratios of worms did not differ significantly from 1.0. Unlike most natural collections, the mean intensity of infection was above 1.0, and infection did not appear to preclude the host from mating.     

Reproductive strategies of two sympatric species of Hyalella Smith, 1874 (Amphipoda,Dogielinotidae) in laboratory conditions

This study was performed in order to test theoretical predictions that sympatric species might show different reproductive strategies to facilitate their coexistence. The duration of precopulatory mate‐guarding behaviour, body size of ovigerous females, embryonic and postembryonic development time, fecundity, and viability of the sympatric amphipod species Hyalella pleoacuta and H. castroi were investigated under laboratory conditions (19±1°C and 12 h light/dark photoperiod). Specimens were collected with nets in autumn and spring 2004, and summer and winter 2005 in the Vale das Trutas, São José dos Ausentes County, southern Brazil, and transported to the laboratory. Both species of Hyalella showed similar reproductive strategies, especially in respect to the duration of the precopula, duration of the embryonic period, and fecundity. However, these species differed in body size of ovigerous females, duration of the postembryonic period, viability, and body size of juveniles that remained in the marsupium and those released by females. These differences in the reproductive traits of H. pleoacuta and H. castroi may facilitate their coexistence in nature.     

Microhabitat-specific controls on soil respiration and denitrification in the Mojave Desert: the role of harvester ant nests and vegetation

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.     

Studies of a uniparental form of Aphytis vandenboschi (Hymenoptera: Aphelinidae), a parasite of the San Jose Scale in northern Utah

The only San Jose scale parasite found at two sites in northern Utah was a uniparental form of Aphytis vandenboschi DeBach & Rosen. Parasites overwintered as pupae and were attracted to San Jose scale pheromone traps. Mature female scales were most heavily parasitized, although some prepupal males and instar II female scales were attacked. Only partial development occurred between 11.7 and 18.3 C, and fecundity was reduced between 28 and 31 C. Based on 11.7 C, 460 degree days were required in the field and 410 degree days at 26 C in the laboratory per generation. By the end of the season during 1981 at Brigham City, 30.9% of the adult scales on twigs and 79.2% on leaves were parasitized. During 1982, parasitism was 21.1% on twigs and 70.9% on leaves. A mite, Pyemotes herfsi (Oudemans), was a major predator of Aphytis in both laboratory cultures and field populations.     

Evaluation of fish diplostomatosis in Strawberry Reservoir following rotenone application: a five-year study

Strawberry Reservoir, Wasatch County, Utah, was treated with rotenone in August 1990. For 5 yr following treatment, about 2000 fish from 5 different species were examined for eye metacercariae ( Diplostomum ). Incidence dropped from 88.0% before to 0.1% after treatment for cutthroat trout ( Oncorhynchus clarki ), from 93.0% to 0.1% for rainbow trout ( O. mykiss ), and from 19.0% to 10.0% for redside shiner ( Richardsonius balteatus ). Average numbers of metacercariae per eye also dropped from 6.8 to 0.1 for cutthroat trout, from 23.1 to 0.1 for rainbow trout, and from 18.9 to 0.1 for redside shiner. Kokanee salmon ( O.nerka ), introduced into the reservoir 1 yr after treatment, had a 0.9% prevalence rate and average of 0.1 metacercariae per eye. Rotenone affected almost all organisms in the system. Low incidence of diplostomatosis after treatment indicates that rotenone effectively destroyed many intermediate hosts (fish, snails), which in turn probably affected parasite burdens in definitive hosts (gulls). These changes in metacercariae per host probably occurred because of the complex life cycle of the organism, which is similar to the other trematodes. Rotenone is a specific inhibitor of electron transport complex I and can be devastating to parasites with complex life cycles. Through a combination of factors, parasite numbers have decreased in Strawberry Reservoir.     

Effect of salinity on seed germination of Triglochin maritima under various temperature regimes

Triglochin maritima L. (arrow grass), an herbaceous perennial in the family Juncaginacea, is widely distributed in inland and coastal salt marshes of North America. Triglochin maritima seeds from a population growing in a salt marsh at Faust, Utah, were germinated at 4 temperature regimes (12-h night/12-h day, 5-15° C, 10-20° C, and 15-25° C) and 5 salinities (0, 100, 200, 300, 400, and 500 mol m -3 NaCl) to determine optimal conditions for germination and level of salt tolerance. Ungerminated seeds were returned to distilled water after 20 d to determine whether seeds could recover from salinity treatments. Maximum germination occurred in distilled water, and increases in NaCl concentration progressively inhibited seed germination. No seeds germinated at concentrations higher than 400 mol m -3 NaCl. A temperature regime of low night (5° C) and high day (25° C) temperature yielded maximum germination; all other temperature regimes significantly inhibited seed germination relative to this optimum. Recovery of germination was highest at 5-25° C and lowest at 5-15° C. Recovery of seed germination when seeds were transferred to distilled water from salt solutions was highest at 5-25° C (72%) for seeds exposed to the 500 mol m -3 NaCl pretreatment and significantly reduced at other temperature regimes. The recovery germination response indicates a synergistic inhibitory interaction effect on germination when seeds were exposed to high salinities at suboptimal thermoperiods.     

Field acetylene reduction rates of Lupinus argenteus along an elevational gradient

The effects of elevation and environmental parameters associated with elevation on the dinitrogen fixation rates, N 2 [C 2 H 2 ], of a North American lupine species were evaluated. Lupinus argenteus Pursh plants growing at five elevations on Francis Peak, Utah, were sampled weekly throughout the growing season. The highest elevation site had the greatest frequency of nodulated plants. Influence of the environmental and physiological variables on fixation activity varied with elevation and the mean time of sampling. Soil moisture, nodule dry weight, and air temperature were important. Less than one-half of the observed variation in fixation rates, N 2 [C 2 H 2 ], was accounted for by variation in the associated independent variables. Nevertheless this study documented that nodulated plants of L. argenteus were capable of actively fixing nitrogen at a range of elevations on Francis Peak.     

Aspects of the biology of the Melanesian stick-insect Eurycantha calcarata Lucas (Cheleutoptera: Phasmatidae)

A preliminary account of biological observations on Eurycantha calcarata Lucas is given, based on three years' laboratory data. The development of eggs, nymphs and adults was studied at room temperature (25 ± 1°C) and at 68–72% R.H.     

Vegetation responses to 35 and 55 years of native ungulate grazing in shrubsteppe communities

Ungulate populations are managed in shrubsteppe ecosystems around the world, but relatively few long-term datasets are available that test the impacts of these grazers on shrubsteppe structure and function. This study evaluated 8 exclosures in 4 shrubsteppe communities to determine the effects of deer and elk over 35 or 55 years on (1) plant biomass and species composition, (2) soil nitrogen (N) mineralization and net nitrification rates, Olsen extractable phosphorus (P), and C:N ratios, and (3) arthropod diversity and abundance. The site with deer, the highest ungulate densities, and coldest climate (Sinlahekin Wildlife Area, WA) had greater vegetative biomass and cover inside the exclosures than outside. The sites with elk, moderate ungulate densities, and intermediate climatic conditions (Oak Creek and Wenas Wildlife Areas, WA) had no effects of exclosures on vegetative biomass or cover. The site with elk, the lowest ungulate densities, and driest climatic conditions (L.T. Murray Wildlife Area, WA) had greater shrub cover outside of the exclosures. Ungulates significantly increased net N mineralization and nitrification rates, providing a potential explanation for compensatory growth by grazed plants. Our data suggest that arthropod herbivory does not substitute for ungulate herbivory. To the contrary, arthropod diversity reflected ungulate-induced changes in plant biomass. In addition to effects on standing biomass, ungulates were associated with increased exotic plant species richness at all 4 sites. Our results suggest that there may be a balance between indirect positive and direct negative effects of herbivory on plants that varies with ungulate densities and site characteristics, and that arthropod herbivory does not functionally replace ungulate herbivory.     

Abundance variations and life history traits of two sympatric species of Neotropical annual fish (Cyprinodontiformes: Rivulidae) in temporary ponds of southern Brazil

We investigated abundance variations and life history traits (body size, sex ratio, length–weight relationships and condition factor) of two species of annual fish (Austrolebias minuano Costa and Cheffe and Cynopoecilus fulgens Costa) in temporary ponds of southern Brazil. Six samples were taken from small temporary ponds during three annual seasons over 2 years (2008–2009). A total of 104 individuals of A. minuano and 433 individuals of C. fulgens were collected. The abundance of both species tended to decrease from autumn to spring in the 2 years. The overall sex ratio of A. minuano and C. fulgens were 1.0 male to 1.8 females and 1 male to 1.04 females, respectively. Juveniles of both species occurred only in autumn over the two years and no adult was observed during this season. While the length–weight relationship of A. minuano indicated hyperallometric growth, the relationship of C. fulgens indicated values close to isometric growth.     

Reproductive biology of two species of Hyalella Smith, 1874 (Crustacea: Amphipoda: Hyalellidae) from southern Brazil

Reproduction is a critical event in the life cycle of animals, and a high amount of energy is allocated to it. The aim of this study was to characterize the reproductive biology of two recently described species of Hyalella from the north-east region of state of Rio Grande do Sul in southern Brazil. The specimens were collected during 12 months from a stream source (Hyalella georginae) and from a water reservoir (H. gauchensis), in Palmeira das Missões municipality, state of Rio Grande do Sul. Upon sampling, ovigerous females and pairs in precopulatory behaviour were separated into microtubes. In the laboratory, the cephalothorax length (CL in mm) of all specimens was measured. Male size at onset of sexual maturity was larger than that of the females, in both species. There was a correlation between the size of paired males and females: larger males carried larger females, in both Hyalella species. Precopulatory pairs were found throughout the year; however, H. georginae had a higher frequency in spring, and H. gauchensis in autumn. There was a positive correlation between the CL of ovigerous females and the number of eggs/juveniles. A reduction in the number of eggs throughout the embryonic development was observed in H. georginae. The average fecundity of H. georginae was significantly higher than H. gauchensis. The differences between the reproductive biology of these species may be related to the physical and environmental conditions at which they are exposed in their habitats.     

Effects of temperature and salinity on survival and growth of the amphipod Hyale crassicornis (Gammaridea,Hyalidae)

This study explored the survival and growth of the marine amphipod Hyale crassicornis under different conditions of ambient temperature and salinity in the laboratory. In 96‐h exposure experiments at a salinity of 30, H. crassicornis tolerated temperatures between 6 and 28°C (>90% survival). The 96‐h LT₅₀ value (median lethal temperature) at high temperature range for the amphipod was 32°C. The values at low temperature range for adults and juveniles were 3.2 and 4.2°C, respectively, indicating that adults have a higher tolerance to low temperature than juveniles. At 25°C, the amphipods tolerated salinities between 10 and 50 (with >80% survival in 96?h). The 96‐h LS₅₀ values at high and low salinity ranges were 56 and 2, respectively. Growth of the juveniles from instars 1 to 6 was determined under different combinations of temperature and salinity. Growth rate of juveniles cultured at 25°C and a salinity of 20 was the highest (0.114?mm?day^?1) among the combinations of 15–25°C and 10–40 salinity. The moult increment of body length was affected by both temperature and salinity. Yet the intermoult duration of the amphipods was affected by temperature only but not by salinity.     

Effect of irrigation on survival of third-stage Haemonchus contortus larvae (Nematoda: Trichostrongylidae)

During May through October 1976, samples of sheep pellets containing laboratory - reared, thirdstage Haemonchus contortus larvae were placed on irrigated and nonirrigated pasture plots at Provo, Utah. Periodically thereafter, grass clippings, soil scrapings, and remaining pellets were collected and baermannized to determine their comparative survival from the two environments. Water was added to the irrigated plots in accordance with a weekly sprinkling regime designed to furnish sufficient moisture to maintain pasture grass in this semiarid region. Meteorologic measurements were collected daily from both irrigated and nonirrigated sections.   During the year the nonirrigated section received a total of 131 mm of precipitation, whereas an additional 979 mm of water were added via sprinkling to the irrigated section. The monthly mean maximum temperature at soil surface under grass cover for the six - month study period on the irrigated section averaged 17.7 C less than on the nonirrigated section, and the corresponding soil moisture content remained 14.4 percent higher. A bioclimatograph of conditions on the nonirrigated section showed that none of the months during the year had levels of temperature and moisture which fell within the prescribed limits for optimum pasture transmission of H. contortus; on the irrigated section only October of the six - month study period failed to have suitable conditions for optimum pasture transmission. Larvae placed on the plots survived significantly longer and also in significantly greater numbers on the irrigated section, and irrigation enhanced the ability of larvae to migrate from pellets onto vegetation.     

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.     

Historical variations in δ 13 C leaf of herbarium specimens in the southwestern U.S.

The uncontrolled, global increase in atmospheric CO 2 concentration (ca 80 ppmv) and decline in δ 13 C air (ca 1.5%) since industrialization provide experimental boundary conditions by which to assess physiological response of vegetation. To examine consequences of these global atmospheric changes in the southwestern U.S., 350 specimens of Atriplex confertifolia, A. canescens, Ephedra viridis, Pinus edulis, P. flexilis, Juniperus scopulorum, and Quercus turbinella of precisely known age spanning the last 150 years were acquired from 9 herbaria. Cellulose analysis of δ 13 C plant and estimation of isotopic discrimination (Δ) permitted calculation of water-use efficiency (A/g). The δ 13 C plant chronologies of C 4 Atriplex spp. show some promise as a reliable proxy for δ 13 C air because their mean trends approximate the known δ 13 C air chronology. However, the high variability would necessitate multiple samples at any time period to accurately represent the mean. The generally increasing A/g trends of the 5 C 3 species are particularly pronounced for P. edulis and, after the 1950s, for J. scopulorum, but less evident for P. flexilis, E. viridis, and Q. turbinella, evidencing possible differences in species response to rising CO 2 concentrations. The trends are statistically noisy, however, possibly due to complex microclimates, extreme seasonality, and great interannual variability typical of the southwestern U.S. Herbarium specimens, at least in the Southwest, may be less useful for precise detection of direct CO 2 effects on plant physiology than tree rings, where the variability can be constrained to a single individual over time.     

Carpospore release in a species of Polysiphonia

Intertidal algae from rockpools at different tidal heights, along with Laminaria holdfasts and samples of sublittoral algae were collected from both the sheltered and exposed side of Filey Brigg, North Yorkshire. Samples of sediments were also collected from MLWS on the sheltered shore. A total of 1091 individual ostracods, consisting of 32 species, from 20 genera and 12 families, were identified from 15 sites along the Brigg in July 1996. The current study lists the occurrence of thirteen species previously unrecorded for the Yorkshire coast, and confirms presence of three species that were thought to have a general distribution around the British Isles. The seven Paradoxostoma species showed distinct zonation patterns on both the sheltered and exposed shore. Paradoxostoma ensiforme and P. variabile were only found intertidally, P. hibernicum decreased numerically down shore, and P. bradyi and P. abbreviatum were only found in low shore, Laminaria holdfast or sublittoral samples. This pattern was also seen in many other species, e.g. Xestoleberis aurantia, which only occurred in the intertidal phytal samples, whereas others were only found sublittorally, e.g. Sclerochilus truncatus. Cytherois fischeri, Paradoxostoma robinhoodi, Hemicytherura cellulosa, Leptocythere psammophila, Semicytherura sella and Sclerochilus gewermuelleri were found on the exposed shore only and Cuneocythere semipunctata only occurred on the sheltered shore. Apart from these differences in distribution, the other species occurred on both sides of the Brigg, with only minor differences in density. Some species were more numerous on the sheltered shore (e.g. Heterocythereis albomaculata), whereas others occurred in higher frequencies on the exposed shore (e.g. P. hibernicum). However, there was no marked difference in assemblage structure between the sheltered and exposed side of Filey Brigg. The intertidal phytal assemblages then showed a high degree of similarity. However the sublittoral assemblages were markedly dissimilar from the high-shore assemblages and there was little similarity between the intertidal phytal and sediment assemblages. Although some species occurred in both habitats, e.g. Cythere lutea, others were only found in either one or the other. The phytal assemblages had a higher species richness of ostracods and were more diverse than the sediment assemblages. However, there was no correlation between phytal ostracod species diversity and tidal height, or between diversity and sediment content of the algae. The Yorkshire coast ostracod fauna is compared and contrasted with that previously described by other workers from southern and western Britain.