Dam-forming cacti and nitrogen enrichment in a pi?on-juniper woodland in northwestern Arizona

In a pi?on-juniper woodland in northwestern Arizona, connected basal cladodes of a prickly pear cactus ( Opuntia littoralis var. martiniana ) form check dams that cause deposition of N-rich detritus interspaces otherwise lacking litter. Seventy-eight percent of connected basal cladodes measured in transects grew at an angle (with respect to the slope contour) ≤ 45° -an orientation facilitating deposition of flood-borne debris. Soil total N was significantly greater ( P P = 0.0001) compared to adjacent interspaces. Soil total N and organic C above cactus dams were equal to areas beneath canopies (tree and shrub combined). Net NO 3 - (0-5 cm depth) above cactus dams was significantly greater ( P = 0.0001) than below cactus dams, at interspaces, and beneath canopies. Net NH 4 + (0-5 cm soil depth) above cactus dams was significantly greater ( P s ￣x = 0.625, P = 0.0001).     

Temporal dynamics of invertebrate and aquatic plant communities at three intermittent ponds in livestock grazed Patagonian wetlands

Ponds are recognized worldwide as biodiversity hotspots; nevertheless in Patagonia studies are still needed that reveal the composition and status of their communities. This paper analyses the temporal patterns of aquatic invertebrates and assesses the environmental factors that best predict the variation in community structure at three small intermittent ponds, subjected to ranching practices (summer stocking) in the Patagonian steppe. Variables identified as important in structuring community assemblages were related to environmental conditions (rainfall and water temperature), chemical features (conductivity and pH) and biotic factors (macrophyte coverage). During the connected phase only a small number of invertebrate species were present, in contrast to the 11 taxa that were frequent and abundant during the isolated period (Eucyclops chilensis, Hyalella curvispina and Rhionaeschna sp. were dominant). In this sequence the submersed Myriophyllum quitense and Lilaeopsis macloviana played a crucial role offering habitat and food resources. The present study provides valuable information that can contribute to minimizing the environmental damage and the development of strategies for the conservation of Patagonian wetlands.     

Community structure of Eleodes beetles (Coleoptera: Tenebrionidae) in the shortgrass steppe: scale-dependent uses of heterogeneity

Patterns in the community structure of darkling beetle (9 Eleodes spp., Coleoptera: Tenebrionidae) assemblages in the shortgrass steppe of north central Colorado were monitored by live pitfall trapping for 4 summers. There were significant correlations among weather (temperature and precipitation), species richness, and number of individuals per species captured; effects from weather conditions also displayed 1-month and 1-yr delayed effects. Population densities of 2 eleodid species were monitored by mark-recapture methods. Densities of these species varied relatively little among years and sites, although density was correlated with temperature and precipitation. Abiotic influences on both density and richness differed between 2 macrohabitat types (shortgrass upland, shrub floodplain). The 4 largest species were most abundant in the floodplain, whereas the smallest species was most common in the upland. Affinities with cactus and shrub microhabitats (and an avoidance of bare soil) were evident, although a preference for shaded microhabitats was not detected. These results do not conform well to previous explanations of why darkling beetle assemblages are spatially and temporally heterogeneous, which primarily focused on predation and thermoregulation. Therefore, an alternative mechanism concerning scale-dependent uses of heterogeneity and mobility is proposed to account for eleodid community patterns.     

Observations on the locomotion and buoyancy of Phronima sedentaria (Forskål, 1775) (Crustacea: Amphipoda: Hyperiidea)

The buoyancy and locomotion of the hyperiid amphipod Phronima sedentaria (which lives in barrels constructed from the tissues of gelatinous animals) was studied. The amphipods were much denser than sea water. Barrels were slightly denser than sea water and had six times the mass of the amphipods living within them. Phronima sedentaria swims much more quickly (by a factor of about 3–4) when swimming without its gelatinous barrel. The barrel is asymmetrical with one aperture (entrance) having about three times the area of that of the other (exit). All sustained swimming was accomplished with the larger barrel aperture directed forwards and the significance of this is discussed. Water flow around the barrel and much of the flow through the barrel was laminar; turbulence was limited to the posterior third of the interior of the barrel and was associated with the beating of the pleopods that provide both propulsion and the respiratory current.     

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.     

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.     

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.     

Boggy meadows, livestock grazing, and interspecific interactions: influences on the insular distribution of montane Lincoln's Sparrows ( Melospiza lincolnii alticola )

I surveyed 34 meadows in California and Oregon to count Lincoln's Sparrows ( Melospiza lincolnii alticola ) and to identify habitat features that might influence their local, insular occurrence. Lincoln's Sparrows were most common in wet meadows with little damage by grazing. Singing males were concentrated in flooded or boggy areas near meadow edges, where pines ( Pinus sp.) provided elevated perches for singing and vigilance. Patches of willows ( Salix sp.) were often present nearby. Numbers of male Lincoln's Sparrows were strongly and negatively correlated with abundance of sympatric Song Sparrows ( M. melodia fisherella ). Lincoln's Sparrows breeding in montane meadows are potentially vulnerable to local extirpation because of their insular distribution, low population density, and fluctuating habitat conditions. Heavy damage from livestock grazing drastically increases the probability of local extirpation.     

Redband trout response to hypoxia in a natural environment

Redband trout ( Oncorhynchus mykiss gairdneri ) were observed approximately every 2 weeks in an intermittent southwest Idaho stream between August and December 1991. Instantaneous daytime dissolved oxygen concentration and water temperature declined from 4.0 to Rhinichthys osculus ) were also present in each pool until drying. The response of these fish to such extreme habitat conditions is probably a primary factor accounting for their distribution within arid landscapes.     

Improving seed germination of Salicornia rubra (Chenopodiaceae) under saline conditions using germination-regulating chemicals

Salicornia rubra Nels. (Chenopodiaceae) is a salt-tolerant annual species occurring in salt playas of the Great Basin desert in western United States. It forms pioneer communities on the most saline location of an inland salt playa at Goshen, Utah. Seeds of Salicornia rubra are capable of germinating at 1000 mM NaCl at 25-35° C alternating temperature regime. Dormancy-regulating chemicals were evaluated for their ability to alleviate the innate and salinityenforced dormancy in seeds of Salicornia rubra . Betaine, GA3, kinetin, fusicoccin, ethephon, thiourea, proline, and nitrate had no effect in alleviating primary dormancy. Increases in NaCl concentration progressively inhibited germination of Salicornia rubra seeds. Ethephon, fusicoccin, GA3, kinetin, thiourea, and nitrate promoted germination under low saline conditions. At high salinity fusicoccin had no effect, whereas GA3, kinetin, and ethephon substantially alleviated salinity effects. Application of these dormancy-regulating compounds could be of practical value in seeding a saline area for restoration purposes, particularly under high saline conditions.     

Abundance and ecologic distribution of the shrimp Rimapenaeus constrictus (Crustacea: Penaeidae) on the northern coast of São Paulo State,Brazil

The abundance and ecologic distribution of the shrimp R. constrictus were compared among three different embayments within the northern coast of São Paulo State (23°S, 45°W); i.e. Mar Virado (MV), Ubatuba (UBA) and Ubatumirim (UBM). Key environmental factors were monitored for a better understanding of the distributional patterns of this species, namely temperature, salinity, depth, organic matter content and texture of sediments. In each bay, six transects were delimited, four parallel to the coastline and the other two in areas adjacent to rocky shores. Monthly samples were taken over a 2-year period (1998 and 1999), using a shrimp fishing boat equipped with double-rig nets. Abundance data were treated separately according to environmental characteristics. A total of 4978 specimens was obtained; 921 at MV, 1948 at UBA and 2109 at UBM. The spatial distribution of R. constrictus differed among bays. Higher abundance values were recorded at areas where silt and clay comprised less than 70% of the sediment. A more diversified sediment at UBM and UBA apparently favours the establishment of this species in the region. Its abundance also followed a seasonal trend, higher during spring and summer when intrusions of cold South Atlantic Coastal Waters (SACW) are frequent, promoting the migration of this shrimp to more sheltered areas. These results suggest that sediment type and temperature are the most important variables affecting the spatial and seasonal distribution of this species.     

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.     

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.     

Effects of artificial shading on distribution and abundance of juvenile chinook salmon ( Oncorhynchus tshawytscha )

The influence of artificial shade on the distribution and abundance of juvenile chinook salmon was studied in a side channel of the South Fork Salmon River, Idaho. Fish biomass and abundance were greater in shaded than in unshaded areas when compared to both cumulative incident light reaching the study sections during the 72-hour test runs and instantaneous incident light conditions at the end of the 72-hour test runs. Because conditions may be atypical at the time of instantaneous light measurement, we prefer cumulative incident light for relating light and shade conditions to daytime distribution (abundance and biomass) of juvenile chinook salmon.     

Environmental attributes correlating with density of blackbrush ( Coleogyne ramosissima ) shurbs in the Spring Mountains of southern Nevada

Discovery of distinct mid-elevational bands of blackbrush ( Coleogyne ramosissima Torr.) shrublands on desert mountain slopes in the Mojave Desert caused an investigation of the relationships between environmental factors and Coleogyne distribution. Environmental factors were quantitatively examined to determine which were significant predictors of Coleogyne density at upper-elevational limits (ecotones) in the Spring Mountains of southern Nevada. Path analysis revealed significant, direct causal effects of air temperature, soil moisture, soil depth, and percent litter cover on the distribution of Coleogyne . Specifically, air temperature was a significant positive predictor, while soil moisture, soil depth, and percent litter cover were significant negative predictors of Coleogyne density, with the effects of other environmental variables parceled out. Path analysis also indicated that indirect effects of soil pH, bulk density, compaction, percent pore space, organic matter, soil temperature, salinity, cryptogam, and percent bare soil and rock cover on Coleogyne density were substantially more potent than their direct casual effects. Environmental attributes associated with elevational changes correlate with and may determine the density of Coleogyne shrubs at upper ecotones in southern Nevada.     

Ecological impacts of Pogonomyrmex on woody vegetation of a Larrea-Ambrosia shrubland

Discovery of distinct mid-elevational bands of blackbrush ( Coleogyne ramosissima Torr.) shrublands on desert mountain slopes in the Mojave Desert caused an investigation of the relationships between environmental factors and Coleogyne distribution. Environmental factors were quantitatively examined to determine which were significant predictors of Coleogyne density at upper-elevational limits (ecotones) in the Spring Mountains of southern Nevada. Path analysis revealed significant, direct causal effects of air temperature, soil moisture, soil depth, and percent litter cover on the distribution of Coleogyne . Specifically, air temperature was a significant positive predictor, while soil moisture, soil depth, and percent litter cover were significant negative predictors of Coleogyne density, with the effects of other environmental variables parceled out. Path analysis also indicated that indirect effects of soil pH, bulk density, compaction, percent pore space, organic matter, soil temperature, salinity, cryptogam, and percent bare soil and rock cover on Coleogyne density were substantially more potent than their direct casual effects. Environmental attributes associated with elevational changes correlate with and may determine the density of Coleogyne shrubs at upper ecotones in southern Nevada.     

Vertical distribution of liverwort communities and their relationship with environmental factors in a karst sinkhole in south-western China

ABSTRACT

Understanding the relationships between the vertical distribution of liverwort communities and associated environmental factors is vital for biodiversity conservation in karst sinkholes. The abundance index, α and β diversity indices were used to analyse the characteristics of liverwort communities in the Monkey-Ear Sinkhole (280 m deep, entrance diameter 300 m, width 280 m). A Generalised Linear Model was used to study the vertical distribution of liverwort communities, and the relationships between their vertical distribution and environmental factors were analysed with Canonical Correspondence Analysis. Forty-two liverwort taxa from 22 genera in 19 families were identified in the sinkhole. The liverwort assemblages were dominated by the families Plagiochilaceae and Lejeuneaceae. The α and β diversity appeared to fluctuate randomly among the four depths sampled. The highest degree of environmental heterogeneity was found at the lower-middle section of the sinkhole; liverwort community diversity at the base was much higher than that found at the upper, middle or lower-middle sections. The environment at the base of the sinkhole was more complex than at the other three depths, providing a range of habitats that facilitated the coexistence of multiple liverwort communities. The abundance of species, genera and families in liverwort communities followed the sequence: base > upper section > middle section > lower – middle section. There were significant differences in liverwort communities at the four depths. In the sinkhole, liverwort communities fell into three distribution groups: wide, moderate or narrow distribution along the vertical direction. The communities with a broad distribution, found from the upper section to the base, were affected by a combination of light, humidity and temperature, and were classified as mixed factor dependent; those with a moderate distribution found mostly in the mid and lower-middle sections were primarily dependent on temperature and humidity, and were classified as temperature and humidity dependent; and those with a narrow distribution found at the base of the sinkhole were mainly influenced by humidity, and were classified as humidity dependent.     

American pikas inhabit low-elevation sites outside the species’ previously described bioclimatic envelope

It has been suggested that Nearctic pikas ( Ochotona spp.) are good biogeographic indicators of regions containing rocky, mesic, and cool habitat characterized by long winters and short summers. I examined whether populations of pikas inhabiting distinct low-elevation locales (121–255 m) are faithfully restricted to long-winter and shortsummer conditions by monitoring the climate associated with American pikas ( Ochotona princeps ) in the southern part of the Columbia River Gorge, Oregon. Ambient air temperatures and weather conditions in the vicinity of 4 pika-occupied rockslides were monitored with remote temperature loggers and weather stations from June 2000 to June 2001. Temperatures were compared to long-term averages recorded within the area. I detected pikas inhabiting locales where some temperatures lie outside of the limiting climatic values previously calculated for regions containing pikas. Mild winter temperatures at these pika locations show that long-winter temperatures and snow accumulation associated with typical habitat may not be requirements for pikas in some low-elevation habitat. When using climatic conditions experienced by extant pikas to estimate local paleoenvironments surrounding fossil sites and to anticipate effects of climate change on future pika distributions, I determined that pika sites in the Columbia River Gorge indicate that the association of pikas with long-winter habitat should be considered uncertain. These results highlight the need for further investigation into how local temperatures affect the distribution, behavior, and persistence of low-elevation pikas.     

Description of the biology and immature stages of Pagyris ulla (Hewitson) (Lepidoptera: Nymphalidae: Ithomiini) in the Colombian Andes

The biology and immature stages of Pagyris ulla (Hewitson, [1857]) (Lepidoptera: Nymphalidae: Ithomiini) are described for the first time. The species’ host plant is established to be Brugmansia candida Pers. (Solanaceae). The life cycle from eggs to adult under laboratory conditions and ambient temperature took approximately 47 days, and the larvae passed through five instars. The larvae are gregarious, feed at night, and rest during the day in nests made by joining leaves near the apex of the plant stem.     

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.