Home About us Contact
|
Home About us Contact | ||
|
|
||
Lower Abundance (lower + abundance)
Selected AbstractsRegional and local influence of grazing activity on the diversity of a semi-arid dung beetle communityDIVERSITY AND DISTRIBUTIONS, Issue 1 2006Jorge M. Lobo ABSTRACT This study analyses the effect of resource availability (i.e. sheep dung) on dung beetle communities in an arid region of Central Spain, both at regional and at local scales. A total of 18 sites within 600 km2 were sampled for the regional analysis and 16 sites within the 30 km2 of an Iberian municipality were sampled for the local analysis. Spatial and environmental characteristics of sampling sites were also compiled at both scales, including measures of grazing activity (livestock density at regional scale, and two counts of rabbit and sheep dung at local scale). At a regional scale, any environmental or spatial variable can help to explain the variation in abundance. However, species richness was related to summer precipitation and composition was related to elevation. At local scale, abundance is not significantly related to any of the environmental variables, but species richness was related to the local amount of sheep dung (27% of variance). The amount of dung in a 2-km buffer around the site accounts for 27,32% of variance in abundance and 60,65% of variance in species richness. The presence of the flock with the highest sheep density explains 53% of abundance variability and 73% of species richness variance. A cluster analysis of localities identified two main groups, one characterized by a lower abundance and species richness that can be considered a nested subsample of the species-rich group. The mean and maximum amount of sheep dung in the sites separated by less than 2 km are the only significant explanatory variables able to discriminate both groups. These results suggest that grazing intensity (and the associated increase in the amount of trophic resources) is a key factor in determining local variation in the diversity and composition of dung beetle assemblages. However, dung beetle assemblages are not spatially independent at the analysed resolution, and the amount of dung in the surroundings seems to be more important for locally collected species than the dung effectively found in the site. Although differences in the availability and quantity of trophic resources among nearby sites could be affecting the population dynamics and dispersion of dung beetles within a locality, sites with larger populations, and greater species numbers would not be able to exercise enough influence as to bring about a complete local faunistic homogenization. [source] Diel Changes in Phytoplankton Composition and Abundance in the Surface and Sub-Surface Strata from a Shallow Eutrophic PondINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 1 2009bieta Wilk-Wo, niak Abstract Representative phytoplankton assemblages were identified in a eutrophic pond over a 24 hour period. One assemblage characterized species in the surface (neuston) layer and another consisted of algae from 2, 5, and 20 cm sub-surface depths. The surface layer (0 cm) included a similar, but less diverse assemblage of species, and a lower abundance of cells per unit volume, than those at the lower depths. At each of the sub-surface depths (2,20 cm), the major phytoplankton components initially followed similar patterns of abundance in reference to the time and depth of sample collections then later differed in their abundance levels. The dominant algae were chlorophytes, cryptophytes, diatoms, and cyanobacteria. Mean concentrations of total phytoplankton, over the 24 hours for the surface, were 3.3 × 103 cells ml,1, compared to 36.9 × 103 cells ml,1 for depths 2,20 cm. The autotrophic picoplankton abundance was recorded separately from the phytoplankton with mean concentrations of 472.9 × 103 cells ml,1 in the surface layer and 623.0 × 103 cells ml,1 for the three sub-surface depths. Photos of representative species from these surface layers are presented. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Fine-scale heterogeneity in beetle assemblages under co-occurring Eucalyptus in the same subgenusJOURNAL OF BIOGEOGRAPHY, Issue 10 2010Philip S. Barton Abstract Aim, Insect biodiversity is often positively associated with habitat heterogeneity. However, this relationship depends on spatial scale, with most studies focused on differences between habitats at large scales with a variety of forest tree species. We examined fine-scale heterogeneity in ground-dwelling beetle assemblages under co-occurring trees in the same subgenus: Eucalyptus melliodora A. Cunn. ex Schauer and E. blakelyi Maiden (Myrtaceae). Location, Critically endangered grassy woodland near Canberra, south-eastern Australia. Methods, We used pitfall traps and Tullgren funnels to sample ground-dwelling beetles from the litter environment under 47 trees, and examined differences in diversity and composition at spatial scales ranging from 100 to 1000 m. Results, Beetle assemblages under the two tree species had distinctive differences in diversity and composition. We found that E. melliodora supported a higher richness and abundance of beetles, but had higher compositional similarity among samples. In contrast, E. blakelyi had a lower abundance and species richness of beetles, but more variability in species composition among samples. Main conclusions, Our study shows that heterogeneity in litter habitat under co-occurring and closely related eucalypt species can influence beetle assemblages at spatial scales of just hundreds of metres. The differential contribution to fine-scale alpha and beta diversity by each eucalypt can be exploited for conservation purposes by ensuring an appropriate mix of the two species in the temperate woodlands where they co-occur. This would help not only to maximize biodiversity at landscape scales, but also to maintain heterogeneity in species richness, trophic function and biomass at fine spatial scales. [source] Effects of the past and the present on species distribution: land-use history and demography of wintergreenJOURNAL OF ECOLOGY, Issue 2 2000Kathleen Donohue Summary 1,Past land use can have long-term effects on plant species' distributional patterns if alterations in resources and environmental conditions have persistent effects on population demography (environmental change) and/or if plants are intrinsically limited in their colonization ability (historical factors). 2,We evaluated the role of environmental alteration vs. historical factors in controlling distributional patterns of Gaultheria procumbens, a woody, clonal understorey species with a pronounced restriction to areas that have never been ploughed, and near absence from adjoining areas that were ploughed in the 19th century. The demographic study was conducted in scrub oak and hardwood plant communities on an extensive sand plain, where it was possible to control for the effect of variation in environment prior to land use. 3,The observed demographic effects were contrary to the hypothesis that persistent environmental alteration depressed demographic performance and limited the distribution of G. procumbens. We observed no overall effect of land-use history on stem density, stem recruitment or flower production. In fact, some aspects of performance were enhanced in previously ploughed areas. Populations in previously ploughed areas exhibited less stem mortality in scrub oak transitions, an increase in germination, seedling longevity and proportion of potentially reproductive stems in both plant communities, a trend for slower observed rates of population decline in both plant communities, and a higher projected rate of population growth in the scrub oak transitions. Thus, particularly in scrub oak communities, the lower abundance of G. procumbens in formerly ploughed than in unploughed areas contrasted with its performance. 4,The limited occurrence of G. procumbens in formerly farmed areas was explained instead by its slow intrinsic growth rate, coupled with limited seedling establishment. Lateral population extension occurred exclusively through vegetative growth, allowing a maximum expansion of 43 cm year,1. 5,We conclude that inherent limitations in the colonizing ability of some plant species may present a major obstacle in the restoration or recovery of plant communities on intensively disturbed sites, even in the absence of persistent environmental effects that depress population growth. [source] Reactions of BBrn+ (n = 0,2) at fluorinated and hydrocarbon self-assembled monolayer surfaces: observations of chemical selectivity in ion,surface scatteringJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2001Nathan Wade Abstract Ion,surface reactions involving BBrn+ (n = 0,2) with a fluorinated self-assembled monolayer (F-SAM) surface were investigated using a multi-sector scattering mass spectrometer. Collisions of the B+ ion yield BF2+ at threshold energy with the simpler product ion BF+· appearing at higher collision energies and remaining of lower abundance than BF2+ at all energies examined. In addition, the reactively sputtered ion CF+ accompanies the formation of BF2+ at low collision energies. These results stand in contrast with previous data on the ion,surface reactions of atomic ions with the F-SAM surface in that the threshold and most abundant reaction products in those cases involved the abstraction of a single fluorine atom. Gas-phase enthalpy data are consistent with BF2+ being the thermodynamically favored product. The fact that the abundance of BF2+ is relatively low and relatively insensitive to changes in collision energy suggests that this reaction proceeds through an entropically demanding intermediate at the vacuum,surface interface, one which involves interaction of the B+ ion simultaneously with two fluorine atoms. By contrast with the reaction of B+, the odd-electron species BBr+· reacts with the F-SAM surface to yield an abundant single-fluorine abstraction product, BBrF+. Corresponding gas-phase ion,molecule experiments involving B+ and BBr+· with C6F14 also yield the products BF+· and BF2+, but only in extremely low abundances and with no preference for double fluorine abstraction. Ion,surface reactions were also investigated for BBrn+ (n = 0,2) with a hydrocarbon self-assembled monolayer (H-SAM) surface. Reaction of the B+ ion and dissociative reactions of BBr+· result in the formation of BH2+, while the thermodynamically less favorable product BH+· is not observed. Collisions of BBr2+ with the H-SAM surface yield the dissociative ion,surface reaction products, BBrH+ and BBrCH3+. Substitution of bromine atoms on the projectile by hydrogen or alkyl radicals suggests that Br atoms may be transferred to the surface in a Br-for-H or Br-for-CH3 transfer reaction in an analogous fashion to known transhalogenation reactions at the F-SAM surface. The results for the H-SAM surface stand in contrast to those for the F-SAM surface in that enhanced neutralization of the primary ions gives secondary ion signals one to two orders of magnitude smaller than those obtained when using the F-SAM surface, consistent with the relative ionization energies of the two materials. Copyright © 2001 John Wiley & Sons, Ltd. [source] Chromosome replication patterns in the hyperthermophilic euryarchaea Archaeoglobus fulgidus and Methanocaldococcus (Methanococcus) jannaschiiMOLECULAR MICROBIOLOGY, Issue 5 2002Sophie Maisnier-Patin Summary We analysed chromosome replication patterns in the two hyperthermophilic euryarchaea Archaeoglobus fulgidus and Methanocaldococcus (Methanococcus) jannaschii by marker frequency analysis (MFA). For A. fulgidus, the central region of the chromosomal physical map displayed a higher relative abundance in gene dosage during exponential growth, with two continuous gradients to a region of lower abundance at the diametrically opposite side of the genome map. This suggests bidirectional replication of the A. fulgidus chromosome from a single origin. The organization of the putative replication origin region relative to the cdc6, mcm and DNA polymerase genes differed from that reported for Pyrococcus species. No single replication origin or termination regions could be identified for M. jannaschii, adding to the list of unusual properties of this organism. The organization of the A. fulgidus cell cycle was characterized by flow cytometry analysis of the samples from which genomic DNA was extracted for MFA. The relative lengths of the cell cycle periods were found to be similar to those of crenarchaea. [source] Gas chromatography,mass spectrometry analyses of volatile organic compounds from potato tubers inoculated with Phytophthora infestans or Fusarium coeruleumPLANT PATHOLOGY, Issue 4 2001B. P. J. De Lacy Costello Volatile organic compounds (VOCs) collected from potato tubers inoculated with Phytophthora infestans (late blight), Fusarium coeruleum (dry rot) or sterilized distilled water (as a control) were analysed using gas chromatography,mass spectrometry (GC,MS) and gas chromatography,flame ionization detection (GC,FID). A total of 52 volatiles were identified by GC,MS in the headspaces above P. infestans- and F. coeruleum- inoculated tubers after incubation for 42 days in the dark at 10°C. Of these VOCs, the six most abundant were common to both pathogens. These were benzothiazole (highest abundance), 2-ethyl-1-hexanol (second highest abundance), and at approximately equal third abundance, hexanal, 2-methylpropanoic acid-2,2-dimethyl-1-(2-hydroxy-1-methylethyl)-propyl ester, 2-methylpropanoic acid-3-hydroxy-2,4,4-trimethyl-pentyl ester and phenol. In addition, styrene also occurred at approximately equal third abundance in the headspace of F. coeruleum- inoculated tubers, but at lower abundance in the headspace of P. infestans- inoculated tubers. Some VOCs were specific to each pathogen. Butanal, 3-methylbutanal, undecane and verbenone were found at low levels only in the headspace of tubers inoculated with P. infestans, while 2-pentylfuran and copaene were found only in the headspace of tubers inoculated with F. coeruleum. Additionally GC,FID analysis identified ethanol and 2-propanol in the liquid exudate from both P. infestans - and F. coeruleum -inoculated tubers after incubation for 35 days, and in the headspace after incubation for 42 days. These data provide key information for developing a sensor-based early warning system for the detection of postharvest diseases in stored potato tubers. [source] Micropreparative fractionation of the complexome by blue native continuous elution electrophoresisPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 9 2009Kuan Yen Huang Abstract The large-scale analysis of protein complexes is an emerging challenge in the field of proteomics. Currently, there are few methods available for the fractionation of protein complexes that are compatible with downstream proteomic techniques. Here, we describe the technique of blue native continuous elution electrophoresis (BN-CEE). It combines the features of blue native PAGE (BN-PAGE) and continuous elution electrophoresis (CEE), generating liquid-phase fractions of protein complexes of up to 800,kDa. The resulting complexes can be further analysed by BN-PAGE, by SDS-PAGE and/or by MS. This can help define the constituent proteins of many complexes and their stoichiometry. As BN-CEE is also micropreparative, with a capacity to separate milligram quantities of protein complexes, it will assist the study of proteins of lower abundance. In this regard, the acrylamide concentration and elution rate during separation can be controlled to help ,zoom in' on particular high mass regions and thus complexes of interest. We illustrate the utility of the technique in the analysis of Saccharomyces cerevisiae cellular lysate. [source] Early manganese-toxicity response in Vigna unguiculata L. , a proteomic and transcriptomic studyPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 1 2008Hendrik Führs Abstract The apoplast is known to play a predominant role in the expression of manganese (Mn) toxicity in cowpea (Vigna unguiculata L.) leaves. To unravel early Mn-toxicity responses after 1,3,days Mn treatment also in the leaf symplast, we studied the symplastic reactions induced by Mn in two cultivars differing in Mn tolerance on a total cellular level. Comparative proteome analyses of plants exposed to low or high Mn allowed to identify proteins specifically affected by Mn, particularly in the Mn-sensitive cowpea cultivar. These proteins are involved in CO2 fixation, stabilization of the Mn cluster of the photosystem II, pathogenesis-response reactions and protein degradation. Chloroplastic proteins important for CO2 fixation and photosynthesis were of lower abundance upon Mn stress suggesting scavenging of metabolic energy for a specific stress response. Transcriptome analyses supported these findings, but additionally revealed an upregulation of genes involved in signal transduction only in the Mn-sensitive cultivar. In conclusion, a coordinated interplay of apoplastic and symplastic reactions seems to be important during the Mn-stress response in cowpea. [source] Albumin depletion of human plasma also removes low abundance proteins including the cytokinesPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 18 2005Jill Granger Abstract The use of proteomics for efficient, accurate, and complete analysis of clinical samples poses a variety of technical challenges. The presence of higher abundance proteins in the plasma, such as albumin, may mask the detection of lower abundance proteins such as the cytokines. Methods have been proposed to deplete the sample of these higher abundance proteins to facilitate detection of those with lower abundance. In this study, a commercially available albumin depletion kit was used to determine if removal of albumin would measurably reduce detection of lower abundance cytokine proteins in human plasma. The Montage® Albumin Deplete Kit (Millipore) was used to deplete albumin from LPS-stimulated whole blood from 15 normal human donors. Albumin depletion was measured using the BCG reagent and SDS-PAGE, and cytokine recovery was determined by a microassay immunoassay that measures both pro- and anti-inflammatory cytokines. Average albumin depletion from the samples was 72%. However, several cytokines were also significantly reduced when the albumin was removed from the plasma. Additionally, there was a variable reduction in cytokine recovery from a known mixture of cytokines in a minimal amount of plasma that were loaded onto the columns. These data demonstrate that there may be a non-specific loss of cytokines following albumin depletion, which may confound subsequent proteomic analysis. [source] Comparison of alternative analytical techniques for the characterisation of the human serum proteome in HUPO Plasma Proteome ProjectPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 13 2005Xiaohai Li Abstract Based on the same HUPO reference specimen (C1-serum) with the six proteins of highest abundance depleted by immunoaffinity chromatography, we have compared five proteomics approaches, which were (1) intact protein fractionation by anion-exchange chromatography followed by 2-DE-MALDI-TOF-MS/MS for protein identification (2-DE strategy); (2) intact protein fractionation by 2-D HPLC followed by tryptic digestion of each fraction and microcapillary RP-HPLC/microESI-MS/MS identification (protein 2-D HPLC fractionation strategy); (3) protein digestion followed by automated online microcapillary 2-D HPLC (strong cation-exchange chromatography (SCX)-RPC) with IT microESI-MS/MS; (online shotgun strategy); (4) same as (3) with the SCX step performed offline (offline shotgun strategy) and (5) same as (4) with the SCX fractions reanalysed by optimised nanoRP-HPLC-nanoESI-MS/MS (offline shotgun-nanospray strategy). All five approaches yielded complementary sets of protein identifications. The total number of unique proteins identified by each of these five approaches was (1) 78, (2) 179, (3) 131, (4) 224 and (5) 330 respectively. In all, 560 unique proteins were identified. One hundred and sixty-five proteins were identified through two or more peptides, which could be considered a high-confidence identification. Only 37 proteins were identified by all five approaches. The 2-DE approach yielded more information on the pI -altered isoforms of some serum proteins and the relative abundance of identified proteins. The protein prefractionation strategy slightly improved the capacity to detect proteins of lower abundance. Optimising the separation at the peptide level and improving the detection sensitivity of ESI-MS/MS were more effective than fractionation of intact proteins in increasing the total number of proteins identified. Overall, electrophoresis and chromatography, coupled respectively with MALDI-TOF/TOF-MS and ESI-MS/MS, identified complementary sets of serum proteins. [source] Links between habitat degradation, and social group size, ranging, fecundity, and parasite prevalence in the Tana River mangabey (Cercocebus galeritus)AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2009David N.M. Mbora Abstract We investigated the effects of anthropogenic habitat degradation on group size, ranging, fecundity, and parasite dynamics in four groups of the Tana River mangabey (Cercocebus galeritus). Two groups occupied a forest disturbed by human activities, while the other two occupied a forest with no human disturbance. We predicted that the groups in the disturbed forest would be smaller, travel longer distances daily, and have larger home ranges due to low food tree abundance. Consequently, these groups would have lower fecundity and higher parasite prevalence and richness (number of parasite species). We measured the abundance of food trees and anthropogenic activity in the forests, the groups' daily travel distances and home range sizes, and censused social groups over 12 months. We also analyzed fecal samples for gastrointestinal parasites from three of the groups. The disturbed forest had a lower abundance of food trees, and groups in this forest traveled longer distances, had larger home range sizes, were smaller, and had lower fecundity. The groups in the disturbed forest had higher, although not statistically significant, parasite prevalence and richness. This study contributes to a better understanding of how anthropogenic habitat change influences fecundity and parasite infections in primates. Our results also emphasize the strong influence of habitat quality in determining daily travel distance and home range size in primates. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc. [source] Managing the matrix for large carnivores: a novel approach and perspective from cheetah (Acinonyx jubatus) habitat suitability modellingANIMAL CONSERVATION, Issue 1 2006J. R. Muntifering Abstract Effective management within the human-dominated matrix, outside of formally protected areas, is of paramount importance to wide-ranging carnviores. For instance, the largest extant population of cheetahs Acinonyx jubatus currently persists on privately owned Namibian ranchlands, and provides an excellent case study to examine and design matrix conservation approaches. Although human-caused mortality is likely the principal threat to this population, ancedotal evidence suggests that ,bush encroachment', the widespread conversion of mixed woodland and savannah habitats to dense, Acacia -dominated thickets, is another probable threat. A better understanding of cheetah habitat use, outside of protected areas, could be used to directly influence habitat management strategies and design local restoration and conflict mitigation efforts. To identify specific habitat characteristics associated with cheetah use, we used radio-telemetry locations to identify areas used intensively by cheetahs on commercial Namibian farms. We then compared the habitat characteristics of these ,high-use' areas with adjacent ,low-use' areas. A binary logistic regression model correctly categorized 92% of plot locations as high or low use, and suggested that cheetahs may be utilizing ,rewarding patches' with better sighting visibility and greater grass cover. We discuss the possible reasons for kudu Tragelaphus strepsiceros, Namibian cheetahs' preferred prey, exhibiting significantly lower abundance in high-use areas. Using habitat characteristics to identify areas intensively utilized by cheetahs has important implications for guiding future habitat restoration and developing effective predator conflict mitigation efforts. [source] Effects on vegetation composition of a modified forest harvesting and propagation method compared with clear-cutting, scarification and plantingAPPLIED VEGETATION SCIENCE, Issue 2 2008Johan Bergstedt Question: How does the vegetation of boreal forests respond to harvesting and scarification? Location: 650 m a.s.l., central Sweden (61°38' N). Methods: The response of boreal forest vegetation to cutting and scarification was studied in a field trial, which consisted of three treatments plus conventional harvesting as a control in a complete block design with four replicates. The cutting was done 14 years prior to vegetation inventory and scarification and planting were conducted the first or second years after cutting. Results: The species most abundant at higher cutting intensities were crustose lichens, Cladonia spp., Cladina arbuscula, Polytrichum spp. and pioneer mosses, the grass Deschampsia flexuosa, and the tree Betula pubescens, A few species had substantially lower abundance in treatments with higher cutting intensity, notably Hylocomium splendens and Vaccinium myrtillus. Scarification had a strong effect that was different from the one created by cutting. In scarification treatments, Polytrichum spp. were the only species with high abundance; most species had low abundance, i.e. Barbilophozia lycopodioides, Vaccinium vitis-idaea, Pleurozium schreberi, Carex globularis, Empetrum nigrum, Cladina arbuscula, Sphagnum spp. Conclusions: Our results elaborate on the details of the well-known effect of cutting on ground-layer flora, and also give support for the profound and long-lasting effect that soil scarification has on forest vegetation. [source] Freshwater mussel assemblage structure in a regulated river in the Lower Mississippi River Alluvial Basin, USA,AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2007Wendell R. Haag Abstract 1.This paper documents a diverse, reproducing freshwater mussel community (20 species) in Lower Lake , an impounded, regulated portion of the Little Tallahatchie River below Sardis Dam in Panola Co., Mississippi, USA. 2.Despite being regulated and impounded, the lake has a heterogeneous array of habitats that differ markedly in mussel community attributes. Four distinct habitat types were identified based on current velocity and substrate characteristics, representing a gradient from habitats having lotic characteristics to lentic habitats. All four habitat types supported mussels, but habitats most resembling unimpounded, lotic situations (relatively higher current velocity and coarser substrate) had the highest mussel abundance and species density (10.1 mussels m,2, 1.8 species m,2, respectively). Lentic habitats (no flow, fine substrate) were characterized by lower abundance and species density (2.0 mussels m,2, 0.8 species m,2, respectively), but supported mussel assemblages distinctive from lotic habitats. 3.Evidence of strong recent recruitment was observed for most species in the lake and was observed in all four habitat types. 4.Although impounded and regulated, Lower Lake represents one of the few areas of stable large-stream habitat in the region. The presence of a diverse, healthy mussel community in this highly modified habitat suggests that a large component of the regional mussel fauna is relatively resilient and adaptable and is limited primarily by the absence of stable river reaches. Management actions that increase stream stability are likely to result in expansion of the mussel fauna and restoration of a valuable component of ecosystem function in this region. Published in 2006 by John Wiley & Sons, Ltd. [source] Conversion of sagebrush shrublands to exotic annual grasslands negatively impacts small mammal communitiesDIVERSITY AND DISTRIBUTIONS, Issue 5 2009Steven M. Ostoja Abstract Aim, The exotic annual cheatgrass (Bromus tectorum) is fast replacing sagebrush (Artemisia tridentata) communities throughout the Great Basin Desert and nearby regions in the Western United States, impacting native plant communities and altering fire regimes, which contributes to the long-term persistence of this weedy species. The effect of this conversion on native faunal communities remains largely unexamined. We assess the impact of conversion from native perennial to exotic annual plant communities on desert rodent communities. Location, Wyoming big sagebrush shrublands and nearby sites previously converted to cheatgrass-dominated annual grasslands in the Great Basin Desert, Utah, USA. Methods, At two sites in Tooele County, Utah, USA, we investigated with Sherman live trapping whether intact sagebrush vegetation and nearby converted Bromus tectorum -dominated vegetation differed in rodent abundance, diversity and community composition. Results, Rodent abundance and species richness were considerably greater in sagebrush plots than in cheatgrass-dominated plots. Nine species were captured in sagebrush plots; five of these were also trapped in cheatgrass plots, all at lower abundances than in the sagebrush. In contrast, cheatgrass-dominated plots had no species that were not found in sagebrush. In addition, the site that had been converted to cheatgrass longer had lower abundances of rodents than the site more recently converted to cheatgrass-dominated plots. Despite large differences in abundances and species richness, Simpson's D diversity and Shannon-Wiener diversity and Brillouin evenness indices did not differ between sagebrush and cheatgrass-dominated plots. Main conclusions, This survey of rodent communities in native sagebrush and in converted cheatgrass-dominated vegetation suggests that the abundances and community composition of rodents may be shifting, potentially at the larger spatial scale of the entire Great Basin, where cheatgrass continues to invade and dominate more landscape at a rapid rate. [source] Ultraviolet-B Radiation Effects on the Structure and Function of Lower Trophic Levels of the Marine Planktonic Food WebPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2006Gustavo A. Ferreyra ABSTRACT The impact of UV-B radiation (UVBR; 280,320 nm) on lower levels of a natural plankton assemblage (bacteria, phytoplankton and microzooplankton) from the St. Lawrence Estuary was studied during 9 days using several immersed outdoor mesocosms. Two exposure treatments were used in triplicate mesocosms: natural UVBR (N treatment, considered as the control treatment) and lamp-enhanced UVBR (H treatment, simulating 60% depletion of the ozone layer). A phytoplankton bloom developed after day 3, but no significant differences were found between treatments during the entire experiment for phytoplankton biomass (chlorophyll a and cell carbon) nor for phytoplankton cell abundances from flow cytometry and optical microscopy of three phytoplankton size classes (picoplankton, nanoplankton and microplankton). In contrast, bacterial abundances showed significantly higher values in the H treatment, attributed to a decrease in predation pressure due to a dramatic reduction in ciliate biomass (, 70,80%) in the H treatment relative to the N treatment. The most abundant ciliate species were Strombidinium sp., Prorodon ovum and Tintinnopsis sp.; all showed significantly lower abundances under the H treatment. P. ovum was the less-affected species (50% reduction in the H treatment compared with that of the N control), contrasting with ,90% for the other ones. Total specific phytoplanktonic and bacterial production were not affected by enhanced UVBR. However, both the ratio of primary to bacterial biomass and production decreased markedly under the H treatment. In contrast, the ratio of phytoplankton to bacterial plus ciliate carbon biomass showed an opposite trend than the previous results, with higher values in the H treatment at the end of the experiment. These results are explained by the changes in the ciliate biomass and suggest that UVBR can alter the structure of the lower levels of the planktonic community by selectively affecting key species. On the other hand, linearity between particulate organic carbon (POC) and estimated planktonic carbon was lost during the postbloom period in both treatments. On the basis of previous studies, our results can be attributed to the aggregation of carbon released by cells to the water column in the form of transparent exopolymer particles (TEPs) under nutrient limiting conditions. Unexpectedly, POC during such a period was higher in the H treatment than in controls. We hypothesize a decrease in the ingestion of TEPs by ciliates, in coincidence with increased DOC release by phytoplankton cells under enhanced UVBR. The consequences of such results for the carbon cycle in the ocean are discussed. [source] Housing developments in rural New England: effects on forest birdsANIMAL CONSERVATION, Issue 1 2000Daniel A. Kluza In rural New England, forest fragmentation is caused by housing developments in forested areas. To evaluate the effects of these changes on forest birds, we compared bird assemblages between forests with different housing densities in western Massachusetts. Species occurrences and relative abundances were determined from systematic point count surveys and mist-netting at three plots in forest of low housing density (0,0.05 houses/ha) and of moderate housing density (0.60,6.70 houses/ha) in 1993 and 1994. Among guilds, Neotropical migrants and forest-interior species had significantly lower abundances in forests of moderate housing density. Abundances of ground/shrub nesting birds as a group, and of individual species such as veery (Catharus fuscescens), ovenbird (Seiurus aurocapillus) and wood thrush (Hylocichla mustelina), were greater in forest of low housing density, but blue jays (Cyanocitta cristata) were more abundant in forest of moderate housing density. Although the abundances of ground/shrub nesting birds were positively related to ground cover, this vegetation structure did not differ between forest types. Avian and mammalian nest predators may be responsible for the trends in bird abundance. Avian nest predators may recognize forest of moderate housing density as edge habitat, and this rural development may also support relatively high densities of mammalian nest predators. These trends suggest that birds of New England's relatively extensive forests may be subject to greater fragmentation effects than generally thought, as a result of increasing rural housing development within forests. [source] | |||||||||||||