Home About us Contact
|
Home About us Contact | ||
|
|
||
Environmental Parameters (environmental + parameter)
Selected AbstractsSpatial and temporal variations of two cyprinids in a subtropical mountain reserve , a result of habitat disturbanceECOLOGY OF FRESHWATER FISH, Issue 3 2007C.-C. Han Abstract,,, We investigated the variations of population of two cyprinids, Varicorhinus alticorpus and Varicorhinus barbatulus, using long-term survey data (1995,2004) in the subtropical island of Taiwan. Fish abundance data showed that at the mainstem stations, V. barbatulus which used to dominate in the higher altitude had declined significantly, while V. alticorpus that used to occupy only the lower altitude had spread upward. However, at the tributaries, trend of the populations of V. barbatulus were not significantly different over time, while populations of V. alticorpus were absent at higher altitude but began to increase at lower altitude. Environmental parameters revealed that sporadic high turbidity was observed at the mainstem stations, but not at the tributaries. Images taken before and after typhoon also showed habitat destruction by debris flow at the mainstem stations. As some models predicted that suitable fish habitats will shrink because of increasing water temperature due to global warming, we showed that fish distribution may be affected by habitat disturbance due to intensified storms sooner than the actual increase of water temperature. [source] Environmental parameters and anthropogenic effects predicting the spatial distribution of wild ungulates in the Akagera savannah ecosystemAFRICAN JOURNAL OF ECOLOGY, Issue 4 2009Christiane Averbeck Abstract Savannah areas affected by human activities such as livestock keeping and agriculture are often characterized by shifts in landscape structuring, with a predominance of few(er) habitat types. This is typically accompanied by pronounced changes in the communities of ungulates. The aim of this study was to find out whether shifts in ungulate communities in Lake Mburo National Park (LMNP) are primarily predicted by an alteration in the composition of the preferred habitat types or if more complex interactions between habitat changes and the prevalence of ungulates occur. Monthly road counts were used to establish the number of eleven ungulate species in LMNP and adjacent unprotected Ankole Ranching Scheme. The common duiker (Sylvicapra grimmia campbelliae Gray, 1843) was found in more abundance in disturbed areas, while showing a significant change in habitat use. Common duiker tended to use the vegetation type otherwise used by the bushbuck (Tragelaphus scriptus dama Neumann, 1902). Our results support the claim that the occurrence of ungulates is not only directly affected by the availability of ,suitable' habitats, but behavioural plasticity and competitive exclusion also need to be considered. Résumé Les zones de savane touchées par des activités humaines telles que l'élevage de bétail et l'agriculture se caractérisent souvent par des évolutions de la structure du paysage, avec une prédominance d'un (plus) petit nombre de types d'habitats. Cela s'accompagne généralement de changements marqués chez les communautés d'ongulés. Le but de cette étude était de voir si l'on peut s'attendre à des évolutions des communautés d'ongulés dans le Parc National du Lac Mburo du seul fait d'une altération de la composition des types d'habitats préférés ou s'il y a des interactions plus complexes entre les changements de l'habitat et la prévalence des ongulés. Nous avons eu recours à des comptages routiers mensuels pour établir le nombre d'ongulés de onze espèces dans le Parc National du Lac Mburo et dans l'Ankole Ranching Scheme voisin, nonprotégé. Le sylvicapre de Grimm (Sylvicapra grimmia campbelliae Gray, 1843) fut observé en plus grand nombre dans les zones perturbées, et manifestait un changement significatif de l'utilisation de son habitat. Cette espèce avait tendance à utiliser le type de végétation normalement utilisé par le bushbuck (Tragelaphus scriptus dama Neumann, 1902). Nos résultats soutiennent l'affirmation selon laquelle la présence des ongulés n'est pas directement affectée seulement par la disponibilité d'habitats « appropriés », mais qu'il faut aussi envisager une certaine plasticité comportementale et des compétitions menant à des exclusions. [source] Growth and survival of the scallop Lyropecten (=Nodipecten) nodosus (L. 1758) in suspended culture in the Cariaco Gulf (Venezuela) during a non-upwelling periodAQUACULTURE RESEARCH, Issue 9 2003L Freites Abstract Growth and survival of the scallop Lyropecten nodosus were studied in 1997 at two sites (inner and outer Turpialito Bay) during a non-upwelling period normally occurring between August and November. Individuals had an initial shell height of 4.86 cm (SD=1.64 cm). Both experimental groups were held in suspended plastic baskets at the same depth (4 m). Measurements of shell height and dry weights of shell, gonad, digestive gland, remaining tissues and shell biofouling were taken at monthly intervals. Environmental parameters, including temperature, phytoplanktonic biomass, total particulate material (TPM) and associated organic (POM) and inorganic (PIM) fractions, were recorded simultaneously. At the end of the study, significant differences in growth and survival of scallops were observed between the two experimental sites. Scallops maintained inside the bay showed a 22% greater increase in shell height (7.41±0.27 cm) than those placed outside the bay (6.37±0.41 cm). Survival of scallops inside the bay was 31% higher compared with scallops outside. The greater availability of food of phytoplanktonic origin during the first two experimental months (July and August) together with greater POM throughout the whole experimental period except September, at the inner bay site, probably explained survival and growth differences observed between the two locations. Results suggest that, during the non-upwelling period (characterized by low primary productivity and high water temperatures), POM of sedimentary origin may play an important role as an energy source required for metabolic and reproductive activities of L. nodosus. [source] Effects of environmental variables on fish feeding ecology: implications for the performance of baited fishing gear and stock assessmentJOURNAL OF FISH BIOLOGY, Issue 6 2004A. W. Stoner The effectiveness of baited fishing gear ultimately depends upon behaviour of the target species , activity rhythms, feeding motivation, and sensory and locomotory abilities. While any environmental parameter that mediates feeding or locomotion can have an important influence on the active space presented by the bait and fish catchability, few biologists have considered how such variation in behaviour might affect catch per unit effort (CPUE) and the resultant stock abundance estimates or population parameters. This review reveals that environment-related variation in feeding behaviour can act through four different mechanisms: metabolic processes, sensory limitations, social interactions and direct impacts. Water temperature, light level, current velocity and ambient prey density are likely to have largest effects on fish catchability, potentially affecting variation in CPUE by a factor of ten. Feeding behaviour is also density-dependent, with both positive and negative effects. Over time and geographic space a target species can occupy wide ranges of environmental conditions, and in certain cases, spatial and temporal variation in feeding biology could have a larger impact on CPUE than patterns of abundance. Temperature, light and current can be measured with relative facility and corrections to stock assessment models are feasible. Making corrections for biological variables such as prey density and bait competitors will be more difficult because the measurements are often not practical and relationships to feeding catchability are more complex and poorly understood. There is a critical need for greater understanding of how environmental variables affect feeding-related performance of baited fishing gear. A combination of field observations and laboratory experiments will be necessary to parameterize stock assessment models that are improved to accommodate variation in fish behaviour. Otherwise, survey data could reveal more about variation in behaviour than abundance trends. [source] Penguins as oceanographers unravel hidden mechanisms of marine productivityECOLOGY LETTERS, Issue 3 2002Jean-Benoît Charrassin ABSTRACT A recent concept for investigating marine ecosystems is to employ diving predators as cost-effective, autonomous samplers of environmental parameters (such as sea-temperature). Using king penguins during their foraging trips at sea, we obtained an unprecedented high resolution temperature map at depth off the Kerguelen Islands, Southern Ocean, a poorly sampled but productive area. We found clear evidence of a previously unknown subsurface tongue of cold water, flowing along the eastern shelf break. These new results provide a better understanding of regional water circulation and help explain the high primary productivity above the Kerguelen Plateau. [source] Distribution of microbial populations and their relationship with environmental parameters in the coastal waters of Qingdao, ChinaENVIRONMENTAL MICROBIOLOGY, Issue 7 2010Min Wang Summary In order to understand the large-scale distribution of microbial populations simultaneously and their relationship with environmental parameters, flow cytometry was used to analyse samples collected from 46 stations in the coastal waters of Qingdao in spring, 2007. The distribution of virus was significantly and positively correlated with heterotrophic bacteria. Two groups of picophytoplankton (Synechococcus and picoeukaryotes) were detected; however, Prochlorococcus was not found. Picoeukaryotes and nanophytoplankton were abundant in the near-shore waters, whereas Synechococcus was abundant in the off-shore areas. No variation was found in vertical distribution of virus, heterotrophic bacteria, Synechococcus and nanophytoplankton abundances, except picoeukaryotes abundance in the bottom layer was dramatically lower than that in the upper layers. Correlation analyses indicated that the relationship between abiotic variables and heterotrophic bacteria, pico- and nanophytoplankton was closer than that between abiotic variables and virioplankton. Temperature and nutrients were the synchronous factors controlling the growth of heterotrophic bacteria, pico- and nanophytoplankton in the coastal waters of Qingdao in spring. The results suggested that synergistic and antagonistic effects existed among microbial groups. [source] Diversity and abundance of freshwater Actinobacteria along environmental gradients in the brackish northern Baltic SeaENVIRONMENTAL MICROBIOLOGY, Issue 8 2009Karin Holmfeldt Summary Actinobacteria are highly abundant in pelagic freshwater habitats and also occur in estuarine environments such as the Baltic Sea. Because of gradients in salinity and other environmental variables estuaries offer natural systems for examining factors that determine Actinobacteria distribution. We studied abundance and community structure of Bacteria and Actinobacteria along two transects in the northern Baltic Sea. Quantitative (CARD-FISH) and qualitative (DGGE and clone libraries) analyses of community composition were compared with environmental parameters. Actinobacteria accounted for 22,27% of all bacteria and the abundance changed with temperature. Analysis of 549 actinobacterial 16S rRNA sequences from four clone libraries revealed a dominance of the freshwater clusters acI and acIV, and two new subclusters (acI-B scB-5 and acIV-E) were assigned. Whereas acI was present at all stations, occurrence of acII and acIV differed between stations and was related to dissolved organic carbon (DOC) and chlorophyll a (Chl a) respectively. The prevalence of the acI-A and acI-B subclusters changed in relation to total phosphorus (Tot-P) and Chl a respectively. Community structure of Bacteria and Actinobacteria differed between the river station and all other stations, responding to differences in DOC, Chl a and bacterial production. In contrast, the composition of active Actinobacteria (analysis based on reversely transcribed RNA) changed in relation to salinity and Tot-P. Our study suggests an important ecological role of Actinobacteria in the brackish northern Baltic Sea. It highlights the need to address dynamics at the cluster or subcluster phylogenetic levels to gain insights into the factors regulating distribution and composition of Actinobacteria in aquatic environments. [source] THE EVOLUTION OF SPERM-ALLOCATION STRATEGIES AND THE DEGREE OF SPERM COMPETITIONEVOLUTION, Issue 3 2005Paul D. Williams Abstract The prevailing viewpoint in the study of sperm competition is that male sperm-allocation strategies evolve in response to the degree of sperm competition an ejaculate can expect to experience within a given mating. If males cannot assess the degree of sperm competition their ejaculate will face and/or they are unable to facultatively adjust sperm investment in response to perceived levels of competition, high sperm allocation (per mating) is predicted to evolve in the context of high sperm competition. An implicit assumption of the framework used to derive this result is that the degree of sperm competition is unaffected by changes in sperm-allocation strategies. We present theory based on an alternative perspective, in which the degree of sperm competition and the sperm-allocation strategy are coupled traits that coevolve together. Our rationale is that the pattern of sperm allocation in the population will, in part, determine the level of sperm competition by affecting the number of ejaculates per female in the population. In this setting, evolution in sperm-allocation strategies is driven by changes in underlying environmental parameters that influence both the degree of sperm competition and sperm allocation. This change in perspective leads to predictions that are qualitatively different from those of previous theory. [source] ECOLOGICAL BISTABILITY AND EVOLUTIONARY REVERSALS UNDER ASYMMETRICAL COMPETITIONEVOLUTION, Issue 6 2002Fabio Dercole Abstract How does the process of life-history evolution interplay with population dynamics? Almost all models that have addressed this question assume that any combination of phenotypic traits uniquely determine the ecological population state. Here we show that if multiple ecological equilibria can exist, the evolution of a trait that relates to competitive performance can undergo adaptive reversals that drive cyclic alternation between population equilibria. The occurrence of evolutionary reversals requires neither environmentally driven changes in selective forces nor the coevolution of interactions with other species. The mechanism inducing evolutionary reversals is twofold. First, there exist phenotypes near which mutants can invade and yet fail to become fixed; although these mutants are eventually eliminated, their transitory growth causes the resident population to switch to an alternative ecological equilibrium. Second, asymmetrical competition causes the direction of selection to revert between high and low density. When ecological conditions for evolutionary reversals are not satisfied, the population evolves toward a steady state of either low or high abundance, depending on the degree of competitive asymmetry and environmental parameters. A sharp evolutionary transition between evolutionary stasis and evolutionary reversals and cycling can occur in response to a smooth change in ecological parameters, and this may have implications for our understanding of size-abundance patterns. [source] Characterization of bacterial communities in four freshwater lakes differing in nutrient load and food web structureFEMS MICROBIOLOGY ECOLOGY, Issue 2 2005Katleen van der Gucht Abstract The phylogenetic composition of bacterioplankton communities in the water column of four shallow eutrophic lakes was analyzed by partially sequencing cloned 16S rRNA genes and by PCR-DGGE analysis. The four lakes differed in nutrient load and food web structure: two were in a clearwater state and had dense stands of submerged macrophytes, while two others were in a turbid state characterized by the occurrence of phytoplankton blooms. One turbid and one clearwater lake had very high nutrient levels (total phosphorus > 100 ,g/l), while the other lakes were less nutrient rich (total phosphorus < 100,g/l). Cluster analysis, multidimensional scaling and ANOSIM (analysis of similarity) were used to investigate differences among the bacterial community composition in the four lakes. Our results show that each lake has its own distinct bacterioplankton community. The samples of lake Blankaart differed substantially from those of the other lakes; this pattern was consistent throughout the year of study. The bacterioplankton community composition in lake Blankaart seems to be less diverse and less stable than in the other three lakes. Clone library results reveal that Actinobacteria strongly dominated the bacterial community in lake Blankaart. The relative abundance of Betaproteobacteria was low, whereas this group was dominant in the other three lakes. Turbid lakes had a higher representation of Cyanobacteria, while clearwater lakes were characterized by more representatives of the Bacteroidetes. Correlating our DGGE data with environmental parameters, using the BIOENV procedure, suggests that differences are partly related to the equilibrium state of the lake. [source] Distribution and ecophysiology of the nitrifying bacteria emphasizing cultured speciesFEMS MICROBIOLOGY ECOLOGY, Issue 1 2001Hans-Peter Koops Abstract Nitrification is an important factor in the global nitrogen cycle. Therefore, an increasing number of publications deal with in situ studies of natural bacterial populations participating in this process. However, some crucial points complicate suchlike investigations. At the time being, a total of 25 species of ammonia-oxidizers and eight species of nitrite-oxidizers are cultured but the existence of many more species has been indicated by molecular in situ investigations. With that, only a part of the existing nitrifiers has been defined via isolation and subsequent physiological and molecular characterization. Furthermore, the distribution patterns of the distinct species of nitrifiers depend on various environmental parameters. Hence the composition of nitrifying bacterial communities is complex and divers in heterogeneous habitats. In consequence of the above-mentioned problems, the representation of nitrifying community structures obtained from in situ investigations often has been incomplete and unbalanced in many respects. Polyphasic approaches, applying a combination of classical as well as molecular methods in parallel, could help to find the way for overcoming these problems in the future. Isolation and characterization of as many as possible new species seems to be one of the most important missing steps to advance at this way. [source] Discrepancy in glucose and fructose utilisation during fermentation by Saccharomyces cerevisiae wine yeast strainsFEMS YEAST RESEARCH, Issue 7 2004N.J. Berthels Abstract While unfermented grape must contains approximately equal amounts of the two hexoses glucose and fructose, wine producers worldwide often have to contend with high residual fructose levels (>2 g l,1) that may account for undesirable sweetness in finished dry wine. Here, we investigate the fermentation kinetics of glucose and fructose and the influence of certain environmental parameters on hexose utilisation by wine yeast. Seventeen Saccharomyces cerevisiae strains, including commercial wine yeast strains, were evaluated in laboratory-scale wine fermentations using natural Colombard grape must that contained similar amounts of glucose and fructose (approximately 110 g l,1 each). All strains showed preference for glucose, but to varying degrees. The discrepancy between glucose and fructose utilisation increased during the course of fermentation in a strain-dependent manner. We ranked the S. cerevisiae strains according to their rate of increase in GF discrepancy and we showed that this rate of increase is not correlated with the fermentation capacity of the strains. We also investigated the effect of ethanol and nitrogen addition on hexose utilisation during wine fermentation in both natural and synthetic grape must. Addition of ethanol had a stronger inhibitory effect on fructose than on glucose utilisation. Supplementation of must with assimilable nitrogen stimulated fructose utilisation more than glucose utilisation. These results show that the discrepancy between glucose and fructose utilisation during fermentation is not a fixed parameter but is dependent on the inherent properties of the yeast strain and on the external conditions. [source] The onset of downstream movement of juvenile Atlantic salmon, Salmo salar L., in a chalk streamFISHERIES MANAGEMENT & ECOLOGY, Issue 2 2002W. D. RILEY The downstream movements of wild Atlantic salmon, Salmo salar L., from their established feeding territories in the River Itchen, Hampshire, UK, were logged continuously over an 11-month period using a passive integrated transponder (PIT) antenna system. The time of these movements was then related to a number of monitored and calculated environmental parameters. Initial downstream movement of smolts in April was correlated with the onset of darkness, at which time salmon moved from their established feeding territories alone. No relationship was found between the number of smolts migrating and river flow or maximum daily water temperature. The timing of downstream movement of parr between October and March was random with regard to sunset and time of maximum daily water temperature, suggesting the environmental cue that initiates movement may be different outside the spring smolt period. [source] Modelling potential spawning habitat of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) in the Bay of BiscayFISHERIES OCEANOGRAPHY, Issue 1 2007BENJAMIN PLANQUE Abstract Large amplitude variations in recruitment of small pelagic fish result from interactions between a fluctuating environment and population dynamics processes such as spawning. The spatial extent and location of spawning, which is critical to the fate of eggs and larvae, can vary strongly from year to year, as a result of changing population structure and environmental conditions. Spawning habitat can be divided into ,potential spawning habitat', defined as habitat where the hydrographic conditions are suitable for spawning, ,realized spawning habitat', defined as habitat where spawning actually occurs, and ,successful spawning habitat', defined as habitat from where successful recruitment has resulted. Using biological data collected during the period 2000,2004, as well as hydrographic data, we investigate the role of environmental parameters in controlling the potential spawning habitat of anchovy and sardine in the Bay of Biscay. Anchovy potential spawning habitat appears to be primarily related to bottom temperature followed by surface temperature and mixed-layer depth, whilst surface and bottom salinity appear to play a lesser role. The possible influence of hydrographic factors on the spawning habitat of sardine seems less clear than for anchovy. Modelled relationships between anchovy and sardine spawning are used to predict potential spawning habitat from hydrodynamical simulations. The results show that the seasonal patterns in spawning are well reproduced by the model, indicating that hydrographic changes may explain a large fraction of spawning spatial dynamics. Such models may prove useful in the context of forecasting potential impacts of future environmental changes on sardine and anchovy reproductive strategy in the north-east Atlantic. [source] Biodiversity of Belgian groundwater fauna in relation to environmental conditionsFRESHWATER BIOLOGY, Issue 4 2009PATRICK MARTIN Summary 1. The Pleistocene glaciations during the Quaternary appear to have resulted in an impoverished groundwater fauna in northern Europe. Re-colonisation may have occurred either through long-distance dispersal from unglaciated southern areas or from local refugia. 2. The Belgian groundwater fauna was sampled at multiple sites, and its habitats characterised, to assess whether the composition of present-day stygobiotic assemblages can be attributed to either of these mechanisms. 3. A total of 202 sampling sites were selected in four hydrogeographic units of the Meuse River catchment. Sites were equally divided among the saturated and unsaturated zones of fractured aquifers (karst) and within the hyporheic and phreatic zones of porous aquifers. Seventeen environmental parameters were determined in parallel. 4. More than 140 species were recorded, including representatives of the Amphipoda, Cladocera, Copepoda, Hydrachnidia, Isopoda, Oligochaeta, Ostracoda, Mollusca, Syncarida and Nematoda. Thirty stygobiont species were identified, of which 10 species were new to the Belgian fauna, raising the total number of stygobiotic species in Belgium to 41. 5. The frequency of occurrences of stygobiotic species was always low, with 37% of the sampled sites lacking stygobionts. A few species were exclusive to one hydrological zone, although no statistically significant differences were detected in species richness at any of the four hierarchial levels considered (Meuse catchment = region, hydrogeographic units, aquifer type and hydrological zone). 6. Overall, results suggest that the stygobiotic fauna of Belgium is species-poor and mostly comprises widely distributed species with broad ecological tolerances. This supports the view that eurytopic species re-colonised the area by long-distance dispersal from refugia in southern Europe. The virtual absence of endemic species further suggests that the scenario of an ancient fauna that survived in local refugia is of minor importance. [source] A model for predicting the emergence of dragonflies in a changing climateFRESHWATER BIOLOGY, Issue 9 2008OTTO RICHTER Summary 1. Precise models for the phenology of different species are essential for predicting the potential effects of any temporal mismatch of life cycles with environmental parameters under different climate change scenarios. Here we investigated the effects of ambient water temperature on the onset and synchrony of emergence for a widespread European riverine dragonfly, Gomphus vulgatissimus. 2. Long-term field data on the annual emergence from two rivers in northern Germany, and additional data from a laboratory experiment with different temperature regimes, were used to develop a model that predicted the onset of emergence by using mainly the temperature sum (degree days) as a parameter. 3. Model predictions of the onset of emergence fitted the observations well and could be transferred between localities. This was particularly so when weighting early winter temperature data by using a day length and a temperature-response function, implying potential additional control mechanisms for the onset of emergence. 4. We simulated effects of different winter temperature regimes on the emergence curves in order to predict the effects of climate change. These indicated an acceleration of emergence by 6,7 days per 1 °C temperature increase, which is corroborated by the laboratory data and is in the upper range of data published for other dragonflies. [source] Genetic transduction in freshwater ecosystemsFRESHWATER BIOLOGY, Issue 6 2008OLADELE A. OGUNSEITAN Summary 1. Lateral genetic exchange is a profound consequence of the co-existence of viruses (bacteriophages) and bacteria in freshwater ecosystems. Transduction is distinct from other mechanisms of genetic exchange because it is driven by potentially lethal agents external to the donor and recipient cells. Therefore, transduction is reputed to be a major driving force behind the diversity in natural populations and communities of bacteria. 2. Both generalized transduction (where every segment of the donor's genome has equal chance of being transferred to a recipient cell) and specialized transduction (where certain donor gene sequences are transferred at higher frequencies than others based on their proximity to the integration site of the transducing bacteriophage genome) have been demonstrated for various freshwater bacteria. However, these genetic exchange events occur at frequencies that vary widely, from 10,2 to 10,10 transductants per recipient, depending on the influence of various physical, chemical and biotic environmental factors on the outcome of phage,host encounters. Methodological constraints limit the interpretation of results from early studies of transduction in freshwaters because those studies introduced exogenous organisms in microcosms and excluded, to different extents, naturally occurring environmental conditions and their variability. 3. To assist the design and extrapolation of empirical observations, mathematical models including application of Group Theory are useful to estimate boundaries of the impact of transduction in generating and maintaining microbial diversity in freshwater. These theoretical excursions generate hypotheses and questions that can only be answered through refinement of current empirical estimates of transduction frequency, polarity of gene mobilization, bacteriophage host ranges, and the influence of gradients in environmental parameters that characterize freshwater ecosystems. [source] Assessment of European streams with diatoms, macrophytes, macroinvertebrates and fish: a comparative metric-based analysis of organism response to stressFRESHWATER BIOLOGY, Issue 9 2006DANIEL HERING Summary 1. Periphytic diatoms, macrophytes, benthic macroinvertebrates and fish were sampled with standard methods in 185 streams in nine European countries to compare their response to degradation. Streams were classified into two main stream type groups (i.e. lowland, mountain streams); in addition, the lowland streams were grouped into four more specific stream types. 2. Principal components analysis with altogether 43 environmental parameters was used to construct complex stressor gradients for physical,chemical, hydromorphological and land use data. About 30 metrics were calculated for each sample and organism group. Metric responses to different stress types were analysed by Spearman Rank Correlation. 3. All four organism groups showed significant response to eutrophication/organic pollution gradients. Generally, diatom metrics were most strongly correlated to eutrophication gradients (85% and 89% of the diatom metrics tested correlated significantly in mountain and lowland streams, respectively), followed by invertebrate metrics (91% and 59%). 4. Responses of the four organism groups to other gradients were less strong; all organism groups responded to varying degrees to land use changes, hydromorphological degradation on the microhabitat scale and general degradation gradients, while the response to hydromorphological gradients on the reach scale was mainly limited to benthic macroinvertebrates (50% and 44% of the metrics tested correlated significantly in mountain and lowland streams, respectively) and fish (29% and 47%). 5. Fish and macrophyte metrics generally showed a poor response to degradation gradients in mountain streams and a strong response in lowland streams. 6. General recommendations on European bioassessment of streams were derived from the results. [source] Species richness and spatial distribution of blackflies (Diptera: Simuliidae) in streams of Central Amazonia, BrazilFRESHWATER BIOLOGY, Issue 1 2002Neusa Hamada 1.,The spatial distribution and species richness of blackflies were evaluated at 58 stream sites in Central Amazonia, Brazil. Samples were taken along a north,south axis of approximately 130 km and a east,west axis of approximately 220 km. 2.,Based on stream-site characteristics, the occurrence of larvae of the six most frequently collected species was highly predictable (79.3,91.5% accuracy in prediction of occurrence). The predictive value of stream size and the presence of impoundments agrees with results of similar work in the Holarctic Region, suggesting a general responses of blackflies to environmental parameters. 3.,Although only 19.0% of interstream variation in species richness was explained by a regression model, results suggested that species richness was greater in larger, cooler, faster, covered streams with rocky beds than in smaller, warmer, slower, open streams with sandy bottoms. Overall, the species richness of blackflies (11 species in total) was lower than in the temperate zone suggesting, for some taxa at least, that aquatic communities do not follow the terrestrial pattern of greater species richness in the tropics. [source] Biological energy requirements as quantitative boundary conditions for life in the subsurfaceGEOBIOLOGY, Issue 4 2004T. M. HOEHLER ABSTRACT All life requires energy, which must be extracted from the environment. For all known life, free energy must be available at finite minimum levels in order to be usefully harnessed and must be delivered at finite minimum rates in order to support basic biochemical integrity and function. While seldom tested in the high energy light- and oxygen-based metabolisms of the surface biosphere, the magnitude of these requirements , the biological energy quantum (BEQ) and maintenance energy (ME) requirements, respectively , is considerable with respect to the potential metabolisms and energy sources that characterize the deep subsurface realm. As such, they constitute a fundamental constraint on the possible nature, distribution, and activity of microbial life in that environment. Because the energy released in a chemical transformation can be equated to the concentrations of substrates and products, both the BEQ and ME requirements define the minimum substrate concentration and minimum substrate production rate that must be sustained by a given environment for it to be capable of supporting life. The magnitudes of the BEQ and ME requirements are sensitive to a range of environmental parameters that may vary significantly in the subsurface. Temperature exerts a particularly strong control and is among the most important parameters to be considered in evaluating the energetic habitability of subsurface environments. [source] Late Miocene fish otoliths from the Colombacci Formation (Northern Apennines, Italy): implications for the Messinian ,Lago-mare' eventGEOLOGICAL JOURNAL, Issue 5 2006Giorgio Carnevale Abstract A fish otolith assemblage from the Messinian ,Lago-mare' deposits of the Colombacci Formation cropping out in the Montecalvo in Foglia Syncline, Marche, central Italy, is described. The assemblage displays a low diversity and consists of seven taxa belonging to three families: the Gobiidae, Myctophidae and Sciaenidae. Sciaenid otoliths are the most abundant elements representing 88% of the entire assemblage. The palaeoecological analysis reveals a coastal shallow marine environment strongly influenced by continental outflow. The low diversity and high abundance of the euryecious sciaenids are indicative of a very simplified food web, which probably represented an ecological response to the fluctuating environmental parameters and available food resources. The fish remains documented here provide an unambiguous evidence that normal marine conditions were present in the Mediterranean, at least in the upper part of the ,Lago-mare' event, and unquestionably demonstrate that the marine refilling preceded the Mio-Pliocene boundary. These findings clearly demonstrate that fishes, because of their mobility and migratory behaviour, represent a useful tool for the large-scale interpretation of the environmental conditions of the Messinian Mediterranean water body. The necessity of a new scenario of palaeoenvironmental evolution for the post-evaporitic Messinian of the Mediterranean is also discussed. Copyright © 2006 John Wiley & Sons, Ltd. [source] Multiyear to daily radon variability from continuous monitoring at the Amram tunnel, southern IsraelGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2010S. M. Barbosa SUMMARY Radon is a naturally occurring radioactive noble gas generated within mineral grains of uranium bearing rocks by alpha decay from radium. The Amram tunnel (A. Bloch Geophysical Observatory) is a particularly suitable location for the investigation of radon variability. Located in the arid environment of the Arava desert, near Elat, the 170 m tunnel that constitutes the observatory enables radon monitoring in a desert environment and under fairly stable environmental conditions. The analysis of the temporal variability of continuous measurements of radon and environmental parameters at the Amram tunnel over a period of several years shows a complex temporal pattern characterized by non-stationary and multiscale features. Radon concentrations exhibit multiyear variability in the form of a increasing trend of ,1000 Bq m,3 yr,1 in the mean and much larger trends up to ,2500 Bq m,3 yr,1 in the maximum radon levels. Radon concentrations also display strong seasonal patterns, with maxima in summer and minima in winter, ranging from 2.5 kBq m,3 in winter to 35 kBq m,3 in summer. Intraseasonal variability is characterized by very large radon anomalies, with sharp increases of more than 20 kBq m,3 relative to the base level, that occur in spring and summer and last for several days. Daily periodic variability with maxima around midnight appears also in spring and summer, being absent in the cold months. Radon variability at seasonal, intraseasonal and daily timescales is associated with the air temperature outside the tunnel, specifically the temperature gradient between the external environment and the more stable environment inside the tunnel where the measurements are performed. [source] Variation in Serripes groenlandicus (Bivalvia) growth in a Norwegian high-Arctic fjord: evidence for local- and large-scale climatic forcingGLOBAL CHANGE BIOLOGY, Issue 9 2006WILLIAM G. AMBROSE Jr. Abstract We examined the growth rate of the circumpolar Greenland Cockle (Serripes groenlandicus) over a period of 20 years (1983,2002) from Rijpfjord, a high-Arctic fjord in northeast Svalbard (80°10,N, 22°15,E). This period encompassed different phases of large-scale climatic oscillations with accompanying variations in local physical variables (temperature, atmospheric pressure, precipitation, sea ice cover), allowing us to analyze the linkage between growth rate, climatic oscillations, and their local physical and biological manifestations. Standard growth index (SGI), an ontogenetically adjusted measure of annual growth, ranged from a low of 0.27 in 2002 up to 2.46 in 1996. Interannual variation in growth corresponded to the Arctic climate regime index (ACRI), with high growth rates during the positive ACRI phase characterized by cyclonic ocean circulation and a warmer and wetter climate. Growth rates were influenced by local manifestations of the ACRI: positively correlated with precipitation and to a lesser extent negatively correlated with atmospheric pressure. A multiple regression model explains 65% of the variability in growth rate by the ACRI and precipitation at the nearest meteorological station. There were, however, complexities in the relationship between growth and physical variables, including an apparent 1 year lag between physical forcing changes and biological response. Also, when the last 4 years of poor growth are excluded, there is a very strong negative correlation with ice cover on a pan-arctic scale. Our results suggest that bivalves, as sentinels of climate change on multi-decadal scales, are sensitive to environmental variations associated with large-scale changes in climate, but that the effects will be determined by changes in environmental parameters regulating marine production and food availability on a local scale. [source] Life history of a mule (c. 160 AD) from the Roman fort Biriciana/Weißenburg (Upper Bavaria) as revealed by serial stable isotope analysis of dental tissuesINTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 2 2010T. E. Berger Abstract The presence of the osseous remains of at least four mules in a garbage dump at the Roman fort of Biriciana near the town of Weißenburg, Upper Bavaria, dating to c. 160 AD, raised the question as to whether mule breeding was already performed to the north of the Alps during the Middle Roman Empire, or whether these animals still had to be imported from the Mediterranean. Serial analyses of the dental enamel and dentine of a lower fourth premolar and the surrounding alveolar bone of a mandible of a mule in terms of stable strontium isotopic ratios of the apatite, and stable carbon and oxygen isotope ratios of the structural carbonate, were carried out to test whether this individual moved long distances during its lifetime. Since isotopic ratios obtained by serial analysis can be correlated with consecutive ontogenetic stages, it can be assumed that this particular individual experienced significant changes in terms of diet and environmental parameters after its eighth year of life. These changes included a period of residence in a region of high altitude, most likely the Alps considering the location of the Roman fort where the mule was found. The isotopic data obtained do not contradict the assumption that this animal was bred and raised in northern Italy, to frequent later in its adult life the Alps and finally perish at Biriciana/Weißenburg. Copyright © 2008 John Wiley & Sons, Ltd. [source] Temporal Coherence of Chlorophyll a during a Spring Phytoplankton Bloom in Xiangxi Bay of Three-Gorges Reservoir, ChinaINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 6 2009Yao-Yang Xu Abstract Algal bloom phenomenon was defined as "the rapid growth of one or more phytoplankton species which leads to a rapid increase in the biomass of phytoplankton", yet most estimates of temporal coherence are based on yearly or monthly sampling frequencies and little is known of how synchrony varies among phytoplankton or of the causes of temporal coherence during spring algal bloom. In this study, data of chlorophyll a and related environmental parameters were weekly gathered at 15 sampling sites in Xiangxi Bay of Three-Gorges Reservoir (TGR, China) to evaluate patterns of temporal coherence for phytoplankton during spring bloom and test if spatial heterogeneity of nutrient and inorganic suspended particles within a single ecosystem influences synchrony of spring phytoplankton dynamics. There is a clear spatial and temporal variation in chlorophyll a across Xiangxi Bay. The degree of temporal coherence for chlorophyll a between pairs of sites located in Xiangxi Bay ranged from ,0.367 to 0.952 with mean and median values of 0.349 and 0.321, respectively. Low levels of temporal coherence were often detected among the three stretches of the bay (Down reach, middle reach and upper reach), while high levels of temporal coherence were often found within the same reach of the bay. The relative difference of DIN between pair sites was the strong predictor of temporal coherence for chlorophyll a in down and middle reach of the bay, while the relative difference in Anorganic Suspended Solids was the important factor regulating temporal coherence in middle and upper reach. Contrary to many studies, these results illustrate that, in a small geographic area (a single reservoir bay of approximately 25 km), spatial heterogeneity influence synchrony of phytoplankton dynamics during spring bloom and local processes may override the effects of regional processes or dispersal. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temperate and tropical algal-sea anemone symbiosesINVERTEBRATE BIOLOGY, Issue 2 2001Gisèle Muller-Parker Abstract. In this review, we seek to develop new insights about the nature of algal-sea anemone symbioses by comparing such associations in temperate and tropical seas. Temperate seas undergo pronounced seasonal cycles in irradiance, temperature, and nutrients, while high irradiance, high temperature, and low nutrients are seasonally far less variable in tropical seas. We compare the nature of symbiosis between sea anemones (= actinians) and zooxanthellae (Symbiodinium spp.) in both regions to test tropical paradigms against temperate examples and to identify directions for future research. Although fewer anemone species are symbiotic in temperate regions, they are locally dominant and ecologically important members of the benthic community compared to the tropics. Zooxanthella densities tend to be lower in temperate anemones, but data are limited to a few species in both temperate and tropical seas. Zooxanthella densities are far more stable over time in temperate anemones than in tropical anemones, suggesting that temperate symbioses are more resistant to fluctuations in environmental parameters such as irradiance and temperature. Light-saturated photosynthetic rates of temperate and tropical zooxanthellae are similar, but temperate anemone hosts receive severely reduced carbon supplies from zooxanthellae during winter months when light is reduced. Symbiont transmission modes and specificity do not show any trends among anemones in tropical vs. temperate seas. Our review indicates the need for the following: (1) Investigations of other temperate and tropical symbiotic anemone species to assess the generality of trends seen in a few "model' anemones. (2) Attention to the field ecology of temperate and tropical algal-anemone symbioses, for example, how symbioses function under seasonally variable environmental factors and how zooxanthellae persist at high densities in darkness and winter. The greater stability of zooxanthella populations in temperate hosts may be useful to understanding tropical symbioses in which bleaching (loss of zooxanthellae) is of major concern. (3) Study of the evolutionary history of symbiosis in both temperate and tropical seas. Continued exploration of the phylogenetic relationships between host anemones and zooxanthella strains may show how and why zooxanthellae differ in anemone hosts in both environments. [source] Response surface methodology study of the combined effects of temperature, pH, and aw on the growth rate of Trichoderma asperellumJOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2007B.A.D. Begoude Abstract Aims:, To evaluate the influence of environmental parameters (water activity aw, temperature, and pH) on the radial growth rate of Trichoderma asperellum (strains PR10, PR11, PR12, and 659-7), an antagonist of Phytophthora megakarya, the causal agent of cocoa black pod disease. Methods and Results:, The radial growth of four strains of T. asperellum was monitored for 30 days on modified PDA medium. Six levels of aw (0·995, 0·980, 0·960, 0·930, 0·910, and 0·880) were combined with three values of pH (4·5, 6·5, and 8·5) and three incubation temperatures (20, 25, and 30°C). Whatever the strain, mycelial growth rate was optimal at aw between 0·995 and 0·980, independently of the temperature and pH. Each strain appeared to be very sensitive to aw reduction. In addition, all four strains were able to grow at all temperatures and pH values (4·5,8·5) tested, highest growth rate being observed at 30°C and at pH 4·5,6·5. The use of response surface methodology to model the combined effects of aw, temperature, and pH on the radial growth rate of the T. asperellum strains confirmed the observed results. In our model, growth of the T. asperellum strains showed a greater dependence on aw than on temperature or pH under in vitro conditions. Conclusion:,aw is a crucial environmental factor. Low aw can prevent growth of T. asperellum strains under some conditions. The observed and predicted radial growth rate of strain PR11 showed its greater capacity to support low aw (0·93) as compared with other tested strains at 20°C. This is in agreement with its better protective level when applied in medium-scale trials on cocoa plantations. Significance and Impact of the Study:, This study should contribute towards improving the biocontrol efficacy of T. asperellum strains used against P. megakarya. Integrated into a broader study of the impact of environmental factors on the biocontrol agent,pathogen system, this work should help to build a more rational control strategy, possibly involving the use of a compatible adjuvant protecting T. asperellum against desiccation. [source] The effects of temperature, water activity and pH on the growth of Aeromonas hydrophila and on its subsequent survival in microcosm waterJOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2003M. Sautour Abstract Aims: The influence of temperature, water activity and pH on the growth of Aeromonas hydrophila, and on its survival after transfer in nutrient-poor water were assessed. Methods and Results: Experiments were carried out according to a Box,Behnken matrix at 10,30°C, 0·95,0·99 water activity (aw) and pH 5,9. The effect of each factor on the kinetic parameters of growth (i.e. the maximal specific growth rate, ,max, and the lag time, ,) and on the decline of the bacteria in microcosm water (time to obtain a reduction of 5 log, T5 log) were studied by applying central composite design. Conclusions: The major effect of temperature and water activity on the growth of A. hydrophila was highlighted, whereas the effect of pH in these experimental conditions was not significant. Models describing the effect of environmental parameters on the growth of A. hydrophila were proposed. The effect of the growth environment, and particularly the incubation temperature, have an influence on the survival ability of the bacteria in nutrient-poor water. Significance and Impact of the Study: The Box,Behnken design was well suited to determine the influence of environmental factors on the growth of A. hydrophila and to investigate the effect of previous growth conditions on its survival in microcosm water. [source] The influence of environmental parameters on the abundance, distribution and species composition of macro-invertebrates in Fletcher Reservoir, ZimbabweAFRICAN JOURNAL OF ECOLOGY, Issue 4 2009T. Mwabvu First page of article [source] Factors affecting abundance and distribution of submerged and floating macrophytes in Lake Naivasha, KenyaAFRICAN JOURNAL OF ECOLOGY, Issue 1 2009A. N. Ngari Abstract Macrophytes have been shown to perform important ecological roles in Lake Naivasha. Consequently, various studies regarding the impact of biotic factors on the macrophytes have been advanced but related studies on environmental parameters have lagged behind. In an attempt to address this gap, sampling on floating species and submergents was carried out in eight sampling sites in 2003 to investigate how they were influenced by a set of environmental factors. Soil texture (sandy sediments; P < 0.05, regression coefficient = ,0.749) and wind were the most important environmental parameters influencing the distribution and abundance of floating macrophytes. Combination of soil texture and lake-bed slope explained the most (86.3%) variation encountered in the submergents. Continuous translocation of the floating dominant water hyacinth to the western parts by wind has led to displacement of the submergents from those areas. In view of these findings, the maintenance and preservation of the steep Crescent Lake basin whose substratum is dominated by sand thus hosting most submergents remain important, if the whole functional purpose of the macrophytes is to be sustained. Résumé On a montré que les macrophytes jouent un rôle économique important dans le lac Naivasha. Par conséquent, diverses études ont été réalisées sur l'impact des facteurs biotiques sur les macrophytes, mais les études correspondantes sur les paramètres environnementaux sont à la traîne. Pour essayer de compenser cette lacune, en 2003, on a réalisé un échantillonnage des espèces flottantes et submergées sur huit sites d'échantillonnage pour étudier comment elles étaient influencées par un ensemble de facteurs environnementaux. La texture du sol (sédiments sableux, P < 0,05, coefficient de régression = 0,749) et le vent étaient les paramètres environnementaux les plus important quant à l'influence sur la distribution et l'abondance des macrophytes flottants. La combinaison de la texture du sol et de la pente du fond du lac expliquait la plus grande partie (86,3%) de la variation rencontrée chez les espèces submergées. Le déplacement continuel des jacinthes d'eau, qui est la plante flottante dominante, vers la partie ouest par le vent a entraîné le déménagement des espèces submergées hors de cette partie du lac. Au vu de ces résultats, il est important d'assurer l'entretien et la préservation de la pente raide du bassin du lac en forme de croissant si l'on peut conserver l'ensemble de la fonction des macrophytes. [source] | |||||||||||||||||||||||||||||||||||||||||||