Variation in invertebrate–bryophyte community structure at different spatial scales along altitudinal gradients

Aim This study assessed changes in diversity and assemblage composition in bryophytes and their associated invertebrates along altitudinal gradients in Australia and New Zealand. The importance of altitude in shaping these communities and for the diversity of both invertebrates and bryophytes was examined at different spatial scales, including local, altitudinal, regional and biogeographical. Location Samples were taken from four Australasian mountain ranges between 42° and 43°S: Mt Field and Mt Rufus, Tasmania, Australia, and Otira Valley and Seaward Kaikoura Mountains, South Island, New Zealand. Methods On both Tasmanian mountains, five altitudes were assessed (250, 500, 750, 1000 and 1250 m). At each location (mountain/altitude combination) two sites were chosen and six samples were taken. Six altitudes were assessed on New Zealand mountains (Otira: 250, 500, 750, 1000, 1250 and 1500 m; Kaikoura: 1130, 1225, 1325, 1425, 1525 and 2000 m). Bryophyte substrate was collected, and all samples were stored in 70% ethanol. Invertebrates were extracted from bryophytes using kerosene‐phase separation and all invertebrates were identified to family. At each location in Tasmania, all bryophyte species within six 25‐cm² grids per site were collected and identified to species. Bryophytes from New Zealand were identified to species from the invertebrate sample substrate because of sampling constraints. Results Altitude did have a significant effect on diversity, however, no general trend was found along the altitudinal gradient on the four mountains. There were distinct differences in diversity between biogeographical regions, mountains, altitudes and sites. In Tasmania, Mt Field had the highest diversity in invertebrates and bryophytes at 750 m. In contrast, Mt Rufus had consistent low invertebrate and bryophyte diversity along the entire altitudinal gradient. There were also distinctive differences between locations in the composition of invertebrate and bryophyte communities in Tasmania. Along the two altitudinal gradients in New Zealand, Otira had highest diversity for both invertebrates and bryophytes at low altitudes, whereas Kaikoura had highest invertebrate and lowest bryophyte diversity at the highest altitude. Main conclusions There was an effect of altitude, however, there were no consistent changes in diversity or composition on the four different mountains. There was considerable local and regional variation, and, despite a strong sampling design, no underlying altitudinal trends were detectable. This study demonstrates the importance of examining a range of spatial scales if patterns in community structure along altitudinal gradients are to be studied. The implications of this study are discussed with reference to survey design, taxonomic resolution, climate change and conservation of habitat.     

Pre-winter lipid stores in young-of-year Atlantic salmon along a north–south gradient

The pre-winter lipid stores of young-of-the-year (YOY, age 0 year) Atlantic salmon Salmo salar were analysed along a north–south gradient from c. 71 to 58° N, with winter conditions ranging from >200 days of ice cover to no ice. The rivers sampled in Northern Norway represent some of the most northerly S. salar rivers. There was an increase in lipid content with increasing latitude, and mean lipid content (size adjusted to common mass) for YOY in northern rivers were almost three times higher: 0·035 g compared to 0·013 g in southern rivers. The relationship was not sensitive to variation in sampling time or variation in YOY body size. The lipid stores, however, varied markedly between rivers and also between neighbouring rivers, indicating different strategies or opportunities for pre-winter lipid storage both at latitudinal and local scales.     

Nesting habitat of Warbling Vireos across an elevational gradient in the southern Sierra Nevada

ABSTRACT.   Populations of Warbling Vireos ( Vireo gilvus ) are declining in California, apparently due to low reproductive success. From 1989–2002, I studied the nest-site selection and reproductive success of Warbling Vireos across an elevational gradient in the southern Sierra Nevada. Warbling Vireos regularly nested in upland coniferous forests with few or no deciduous trees, and tree species used by nesting vireos included five species of conifers and four species of deciduous trees. Overall, hardwoods were used more than expected based on their availability, but 69% of all nests were in conifers. Hardwood trees were found only in low and mid-elevation ponderosa pine ( Pinus ponderosa ) and mixed-conifer sites. In low-elevation ponderosa pine habitat, 87% of nests were in hardwoods, with 67% in California black oaks ( Quercus kelloggii ), a species that typically occupies upland sites. In mixed-conifer sites where reproductive success was high, 65% of nests were in incense cedar ( Calocedrus decurrens ) and California black oak was the next most commonly used species. Because fire suppression has likely increased numbers of shade-tolerant tree species like incense cedar, shade-intolerant species like black oaks may have been more important as a nest substrate for vireos in the past. Only conifers were used as nesting substrates at higher elevations. Nest success was greater for Warbling Vireos that nested in tall trees in areas with high basal area. My results suggest that Warbling Vireos in the Sierra Nevada would benefit from management activities that encourage retention and recruitment of California black oaks at lower elevations, and development of stands with large trees, dense foliage, and semi-open canopy throughout their elevation range.     

Rosette scrub occurrence and fog availability in arid mountains of Mexico

Abstract. Large succulent leaf rosettes are a characteristic life form in many deserts. In certain areas they become the dominant life form, creating a vegetation type indicated as rosette scrub. The large number of rosette species suggests a close relationship between form and environment. Rosettes are excellent harvesters of low‐intensity rains and fogs. We propose that some rosette‐dominated formations of the Mexican mountains, namely the montane rosette scrub, occur in altitudinal belts around mountains where fog is abundant. We sampled four altitudinal gradients in mountains with different flora recording the abundance and richness of plants. At one site, the Tehuacán Valley, we also measured the quantity of fog along the gradient, below, above and in the rosette scrub for one year. We found that the abundance and richness of succulent rosette species are strongly associated with altitude, showing maximum values in the well‐defined elevational belts where the montane rosette scrub occurs. Other life forms, such as stem succulent cacti or woody shrubs, do not show this mid‐elevation pattern. The altitudinal ranges where the montane rosette scrub occurs usually coincide with areas where clouds and fog form. Our micrometeorological measurements indicate that rosette plants growing within a cloud belt can increase their water supply by 10–100% by harvesting fog. Outside these belts fog harvest is negligible. Desert rosettes constitute one of the most common fog‐harvesting growth forms.     

Viral pyrogen affects thermoregulatory behavior of wintering Planorbarius corneus (L.) snails (Mollusca: Gastropoda)

Exogenous pyrogens, isolated from viruses, bacteria and fungi, are widely used in research on fever in endotherms. The present study investigates the use of viral pyrogen poly (I:C) for inducing the symptoms of so-called behavioral fever in ectothermic animals Planorbarius corneus (Mollusca: Gastropoda). The observations of thermoregulatory behavior of the snails placed in the temperature gradient showed that the snails which were injected with 750 ng g⁻¹ polyinosinic-polycytidylic acid-poly (I:C), after remaining latent for more than 24 h, moved to warmer areas (with the temperature around 30 °C) and stayed there until the end of the experiment. Transferred to the culture, they lived for a period similar to that of the control snails. Our observations indicate that P. corneus snails can exhibit a symptoms of fever response to poly (I:C) and could be used as model animals in the research on behavioral fever in invertebrates.     

Osmotic properties of the sealed tubular system of toad and rat skeletal muscle

A method was developed that allows conversion of changes in maximum Ca(2+)-dependent fluorescence of a fixed amount of fluo-3 into volume changes of the fluo-3-containing solution. This method was then applied to investigate by confocal microscopy the osmotic properties of the sealed tubular (t-) system of toad and rat mechanically skinned fibers in which a certain amount of fluo-3 was trapped. When the osmolality of the myoplasmic environment was altered by simple dilution or addition of sucrose within the range 190-638 mosmol kg(-1), the sealed t-system of toad fibers behaved almost like an ideal osmometer, changing its volume inverse proportionally to osmolality. However, increasing the osmolality above 638 to 2,550 mosmol kg(-1) caused hardly any change in t-system volume. In myoplasmic solutions made hypotonic to 128 mosmol kg(-1), a loss of Ca(2+) from the sealed t-system of toad fibers occurred, presumably through either stretch-activated cationic channels or store-operated Ca(2+) channels. In contrast to the behavior of the t-system in toad fibers, the volume of the sealed t-system of rat fibers changed little (by <20%) when the osmolality of the myoplasmic environment changed between 210 and 2,800 mosmol kg(-1). Results were also validated with calcein. Clear differences between rat and toad fibers were also found with respect to the t-system permeability for glycerol. Thus, glycerol equilibrated across the rat t-system within seconds to minutes, but was not equilibrated across the t-system of toad fibers even after 20 min. These results have broad implications for understanding osmotic properties of the t-system and reversible vacuolation in muscle fibers. Furthermore, we observed for the first time in mammalian fibers an orderly lateral shift of the t-system networks whereby t-tubule networks to the left of the Z-line crossover to become t-tubule networks to the right of the Z-line in the adjacent sarcomere (and vice versa). This orderly rearrangement can provide a pathway for longitudinal continuity of the t-system along the fiber axis.     

Phenology of temperate trees in tropical climates

Several North American broad-leaved tree species range from the northern United States at 47°N to moist tropical montane forests in Mexico and Central America at 15–20°N. Along this gradient the average minimum temperatures of the coldest month (T _Jan), which characterize annual variation in temperature, increase from –10 to 12°C and tree phenology changes from deciduous to leaf-exchanging or evergreen in the southern range with a year-long growing season. Between 30 and 45°N, the time of bud break is highly correlated with T _Jan and bud break can be reliably predicted for the week in which mean minimum temperature rises to 7°C. Temperature-dependent deciduous phenology—and hence the validity of temperature-driven phenology models—terminates in southern North America near 30°N, where T _Jan>7°C enables growth of tropical trees and cultivation of frost-sensitive citrus fruits. In tropical climates most temperate broad-leaved species exchange old for new leaves within a few weeks in January-February, i.e., their phenology becomes similar to that of tropical leaf-exchanging species. Leaf buds of the southern ecotypes of these temperate species are therefore not winter-dormant and have no chilling requirement. As in many tropical trees, bud break of Celtis, Quercus and Fagus growing in warm climates is induced in early spring by increasing daylength. In tropical climates vegetative phenology is determined mainly by leaf longevity, seasonal variation in water stress and day length. As water stress during the dry season varies widely with soil water storage, climate-driven models cannot predict tree phenology in the tropics and tropical tree phenology does not constitute a useful indicator of global warming.     

Direct profiling of the yeast dynamics in wine fermentations

We present a method to directly characterize the yeast diversity present in wine fermentations by employing denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)-amplified 26S ribosomal RNA (rRNA) genes. PCR-DGGE of a portion of the 26S rRNA gene was shown to distinguish most yeast genera associated with the production of wine. With this method the microbial dynamics in several model wine fermentations were profiled. PCR-DGGE provided a qualitative assessment of the yeast diversity in these fermentations accurately identifying populations as low as 1000 cells ml(-1). PCR-DGGE represents an attractive alternative to traditional plating schemes for analysis of the microbial successions inherent in the fermentation of wine.     

H+- and K+-Dependence of Ca2+ Uptake in Lung Lamellar Bodies

Lung lamellar bodies maintain an acidic interior by an energy-dependent process. The acidic pH may affect the packaging of surfactant phospholipids, processing of surfactant proteins, or surfactant protein A-dependent lipid aggregation. The electron-probe microanalysis of lamellar body elemental composition has previously suggested that lamellar bodies contain high levels of calcium some of which may be in ionic form. In this study, we investigated the Ca²⁺ uptake characteristics in isolated lung lamellar bodies. The uptake of Ca²⁺ was measured by monitoring changes in the fluorescence of Fluo-3, a Ca²⁺ indicator dye. The uptake of Ca²⁺ in lamellar bodies was ATP-dependent and increased with increasing concentrations of Ca²⁺. At 100 nm Ca²⁺, the uptake was almost completely inhibited by bafilomycin A1, a selective inhibitor of vacuolar type H⁺-ATPase, or by NH₄Cl, which raises the lamellar body pH, suggesting that the pH gradient regulates the uptake. The uptake of Ca²⁺ increased as the Ca²⁺ concentration was increased, but the relative contribution of bafilomycin A1-sensitive uptake decreased. At 700 nm, it comprised only 20% of the total uptake. These results suggest the presence of additional mechanism(s) for uptake at higher Ca²⁺ concentrations. At 700 nm Ca²⁺, the rate and extent of uptake were lower in the absence of K⁺ than in the presence of K⁺. The inhibitors of Ca²⁺-activated K⁺-channels, tetraethylammonium, Penitrem A, and 4-aminopyridine, also inhibited the K⁺-dependent Ca²⁺ uptake at 700 nm Ca²⁺. Thus the uptake of Ca²⁺ in isolated lung lamellar bodies appears to be regulated by two mechanisms, (i) the H⁺-gradient and (ii) the K⁺ transport across the lamellar body membrane. We speculate that lamellar bodies accumulate Ca²⁺ and contribute to regulation of cytosolic Ca²⁺ in type II cells under resting and stimulated conditions. Received: 18 August 1999/Revised: 9 November 1999