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Terrestrial Systems (terrestrial + system)
Selected AbstractsA high-resolution diatom record of late-Quaternary sea-surface temperatures and oceanographic conditions from the eastern Norwegian SeaBOREAS, Issue 4 2002CHRISTOPHER J. A. BIRKS Core MD95-2011 was taken from the eastern Vøring Plateau, near the Norwegian coast. The section between 250 and 750 cm covers the time period from 13 000 to 2700 cal. yr BP (the Lateglacial and much of the Holocene). Samples at 5 cm intervals were analysed for fossil diatoms. A data-set of 139 modern sea-surface diatom samples was related to contemporary sea-surface temperatures (SSTs) using two different numerical methods. The resulting transfer functions were used to reconstruct past sea-surface temperatures from the fossil diatom assemblages. After the cold Younger Dryas with summer SSTs about 6°C, temperatures warmed rapidly to about 13°C. One of the fluctuations in the earliest Holocene can be related to the Pre-Boreal Oscillation, but SSTs were generally unstable until about 9700 cal. yr BP. Evidence from diatom concentration and magnetic susceptibility suggests a change and stabilization of water currents associated with the final melting of the Scandinavian Ice Sheet at c. 8100 cal. yr BP. A period of maximum warmth between 9700 and 6700 cal. yr BP had SSTs 3,5°C warmer than at present. Temperatures cooled gradually until c. 3000 cal. yr BP, and then rose slightly around 2750 cal. yr BP. The varimax factors derived from the Imbrie & Kipp method for sea-surface-temperature reconstructions can be interpreted as water-masses. They show a dominance of Arctic Waters and Sea Ice during the Younger Dryas. The North Atlantic current increased rapidly in strength during the early Holocene, resulting in warmer conditions than previously. Since about 7250 cal. yr BP, Norwegian Atlantic Water gradually replaced the North Atlantic Water, and this, in combination with decreasing summer insolation, led to a gradual cooling of the sea surface. Terrestrial systems in Norway and Iceland responded to this cooling and the increased supply of moisture by renewed glaciation. Periods of glacial advance can be correlated with cool oscillations in the SST reconstructions. By comparison with records of SSTs from other sites in the Norwegian Sea, spatial and temporal changes in patterns of ocean water-masses are reconstructed, to reveal a complex system of feedbacks and influences on the climate of the North Atlantic and Norway. [source] MPE-IFEC: An enhanced burst error protection for DVB-SH systemsBELL LABS TECHNICAL JOURNAL, Issue 1 2009Bessem Sayadi Digital video broadcasting-satellite services to handhelds (DVB-SH) is a new hybrid satellite/terrestrial system for the broadcasting of multimedia services to mobile receivers. To improve the link budget, DVB-SH uses a long interleaver to cope with land mobile satellite (LMS) channel impairments. Multi-protocol encapsulation,inter-burst forward error correction (MPE-IFEC) is an attractive alternative to the long physical interleaving option of the standard and is suited for terminal receivers with limited de-interleaving memory. In this paper, we present a tutorial overview of this powerful error-correcting technique and report new simulation results that show MPE-IFEC improves the quality of broadcast mobile television (TV) reception. © 2009 Alcatel-Lucent. [source] Layered coding for satellite-plus-terrestrial multipath correlated fading channelsINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 5 2004A. Levissianos Abstract This paper introduces two alternative layered-coding (LC) structures suitable for a combination of a geostationary (GEO) satellite and a terrestrial system providing multicasting multimedia services. Both schemes include a RAKE receiver and their performance results are presented under realistic satellite and terrestrial channel conditions. The structures are based on mapping the coded bits either onto 8-PSK symbols or onto QPSK symbols. The LC parameters (such as the interleaver design and the convolutional encoder structures) are analysed and their effect on performance is quantified, especially in cases of highly correlated channels (low vehicular speeds). The various impairments that are associated to the transmission through both terrestrial and satellite correlated fading channels will be taken into account and link level performance results as well as a complexity discussion will be presented. Copyright © 2004 John Wiley & Sons, Ltd. [source] Assemblage level variation in springtail lower lethal temperature: the role of invasive species on sub-Antarctic Marion IslandPHYSIOLOGICAL ENTOMOLOGY, Issue 3 2009CHARLENE JANION Abstract. It is widely held both in the physiological literature, and more generally, that the average characteristics of species within an assemblage differ among sites. Such generalizations should be based on investigations of whole assemblages at sites, but this is rarely done. Here, such a study is undertaken for virtually the full assemblage of springtails found at sub-Antarctic Marion Island, by investigating supercooling points (SCPs) of 12 of the 16 species that occur there. Assemblage level variation tends to be less than that documented for assemblages across northern hemisphere sites but similar to that found at some Antarctic locations. Across this set of species, the mean SCPs of the indigenous species (mean ± SE =,17.2 ± 0.4 °C) do not differ significantly from that of the invasive species (,16.3 ± 0.7 °C). Overall, the introduction of several species to the island does not appear to have led to functional homogenization (for this trait). By combining the assemblage-level SCP data with information on the abundances of the species in each of four major habitats, it is also shown that severe but uncommon low temperature events could substantially alter species relative abundances. By resetting assemblage trajectories, such events could play an important role in the terrestrial system at the island. [source] A cross-system synthesis of consumer and nutrient resource control on producer biomassECOLOGY LETTERS, Issue 7 2008Daniel S. Gruner Abstract Nutrient availability and herbivory control the biomass of primary producer communities to varying degrees across ecosystems. Ecological theory, individual experiments in many different systems, and system-specific quantitative reviews have suggested that (i) bottom,up control is pervasive but top,down control is more influential in aquatic habitats relative to terrestrial systems and (ii) bottom,up and top,down forces are interdependent, with statistical interactions that synergize or dampen relative influences on producer biomass. We used simple dynamic models to review ecological mechanisms that generate independent vs. interactive responses of community-level biomass. We calibrated these mechanistic predictions with the metrics of factorial meta-analysis and tested their prevalence across freshwater, marine and terrestrial ecosystems with a comprehensive meta-analysis of 191 factorial manipulations of herbivores and nutrients. Our analysis showed that producer community biomass increased with fertilization across all systems, although increases were greatest in freshwater habitats. Herbivore removal generally increased producer biomass in both freshwater and marine systems, but effects were inconsistent on land. With the exception of marine temperate rocky reef systems that showed positive synergism of nutrient enrichment and herbivore removal, experimental studies showed limited support for statistical interactions between nutrient and herbivory treatments on producer biomass. Top,down control of herbivores, compensatory behaviour of multiple herbivore guilds, spatial and temporal heterogeneity of interactions, and herbivore-mediated nutrient recycling may lower the probability of consistent interactive effects on producer biomass. Continuing studies should expand the temporal and spatial scales of experiments, particularly in understudied terrestrial systems; broaden factorial designs to manipulate independently multiple producer resources (e.g. nitrogen, phosphorus, light), multiple herbivore taxa or guilds (e.g. vertebrates and invertebrates) and multiple trophic levels; and , in addition to measuring producer biomass , assess the responses of species diversity, community composition and nutrient status. [source] Top-down and bottom-up diversity cascades in detrital vs. living food websECOLOGY LETTERS, Issue 1 2003Lee A. Dyer Abstract Apex predators and plant resources are both critical for maintaining diversity in biotic communities, but the indirect (,cascading') effects of top-down and bottom-up forces on diversity at different trophic levels are not well resolved in terrestrial systems. Manipulations of predators or resources can cause direct changes of diversity at one trophic level, which in turn can affect diversity at other trophic levels. The indirect diversity effects of resource and consumer variation should be strongest in aquatic systems, moderate in terrestrial systems, and weakest in decomposer food webs. We measured effects of top predators and plant resources on the diversity of endophytic animals in an understorey shrub Piper cenocladum (Piperaceae). Predators and resource availability had significant direct and indirect effects on the diversity of the endophytic animal community, but the effects were not interactive, nor were they consistent between living vs. detrital food webs. The addition of fourth trophic level beetle predators increased diversity of consumers supported by living plant tissue, whereas balanced plant resources (light and nutrients) increased the diversity of primary through tertiary consumers in the detrital resources food web. These results support the hypotheses that top-down and bottom-up diversity cascades occur in terrestrial systems, and that diversity is affected by different factors in living vs. detrital food webs. [source] The effects of chronic nitrogen fertilization on alpine tundra soil microbial communities: implications for carbon and nitrogen cyclingENVIRONMENTAL MICROBIOLOGY, Issue 11 2008Diana R. Nemergut Summary Many studies have shown that changes in nitrogen (N) availability affect primary productivity in a variety of terrestrial systems, but less is known about the effects of the changing N cycle on soil organic matter (SOM) decomposition. We used a variety of techniques to examine the effects of chronic N amendments on SOM chemistry and microbial community structure and function in an alpine tundra soil. We collected surface soil (0,5 cm) samples from five control and five long-term N-amended plots established and maintained at the Niwot Ridge Long-term Ecological Research (LTER) site. Samples were bulked by treatment and all analyses were conducted on composite samples. The fungal community shifted in response to N amendments, with a decrease in the relative abundance of basidiomycetes. Bacterial community composition also shifted in the fertilized soil, with increases in the relative abundance of sequences related to the Bacteroidetes and Gemmatimonadetes, and decreases in the relative abundance of the Verrucomicrobia. We did not uncover any bacterial sequences that were closely related to known nitrifiers in either soil, but sequences related to archaeal nitrifiers were found in control soils. The ratio of fungi to bacteria did not change in the N-amended soils, but the ratio of archaea to bacteria dropped from 20% to less than 1% in the N-amended plots. Comparisons of aliphatic and aromatic carbon compounds, two broad categories of soil carbon compounds, revealed no between treatment differences. However, G-lignins were found in higher relative abundance in the fertilized soils, while proteins were detected in lower relative abundance. Finally, the activities of two soil enzymes involved in N cycling changed in response to chronic N amendments. These results suggest that chronic N fertilization induces significant shifts in soil carbon dynamics that correspond to shifts in microbial community structure and function. [source] Factors affecting the degradation of pharmaceuticals in agricultural soils,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2009Sara C. Monteiro Abstract Pharmaceuticals may be released to the soil environment through the application of biosolids to land. To understand those factors affecting the persistence of pharmaceuticals in the soil environment, the present study was performed to assess the effects of soil type, the presence of biosolids, and the impact of chemical mixture interactions on the degradation of three pharmaceuticals: naproxen, carbamazepine, and fluoxetine. Single-compound studies showed that naproxen degraded in a range of soils with half-lives ranging from 3.1 to 6.9 d and in biosolids with a half-life of 10.2 d. No relationships were observed between degradation rate and soil physicochemical properties and soil bioactivity. For naproxen, addition of biosolids to soils reduced the degradation rate observed in the soil-only studies, with half-lives in the soil-biosolid systems ranging from 3.9 to 15.1 d. Carbamazepine and fluoxetine were found to be persistent in soils, biosolids, and soil-biosolid mixtures. When degradation was assessed using a mixture of the three study compounds and the sulfonamide antibiotic sulfamethazine, the degradation behavior of fluoxetine and carbamazepine was similar to that observed in the single compound studies (i.e., no degradation). However, the degradation rate of naproxen in soils, biosolids, and soil-biosolid systems spiked with the mixture was significantly slower than in the single-compound studies. As degradation studies for risk assessment purposes are performed using single substances in soil-only studies, it is possible that current risk assessment procedures will underestimate environmental impacts. Further work is therefore warranted on a larger range of substances, soils, biosolid types, and chemical mixtures to better understand the fate of pharmaceuticals in terrestrial systems. [source] Riverine landscapes: taking landscape ecology into the waterFRESHWATER BIOLOGY, Issue 4 2002JOHN A. WIENS 1.,Landscape ecology deals with the influence of spatial pattern on ecological processes. It considers the ecological consequences of where things are located in space, where they are relative to other things, and how these relationships and their consequences are contingent on the characteristics of the surrounding landscape mosaic at multiple scales in time and space. Traditionally, landscape ecologists have focused their attention on terrestrial ecosystems, and rivers and streams have been considered either as elements of landscape mosaics or as units that are linked to the terrestrial landscape by flows across boundaries or ecotones. Less often, the heterogeneity that exists within a river or stream has been viewed as a `riverscape' in its own right. 2.,Landscape ecology can be unified about six central themes: (1) patches differ in quality (2) patch boundaries affect flows, (3) patch context matters, (4) connectivity is critical, (5) organisms are important, and (6) the importance of scale. Although riverine systems differ from terrestrial systems by virtue of the strong physical force of hydrology and the inherent connectivity provided by water flow, all of these themes apply equally to aquatic and terrestrial ecosystems, and to the linkages between the two. 3.,Landscape ecology therefore has important insights to offer to the study of riverine ecosystems, but these systems may also provide excellent opportunities for developing and testing landscape ecological theory. The principles and approaches of landscape ecology should be extended to include freshwater systems; it is time to take the `land' out of landscape ecology. [source] Nanostructured Bulk Silicon as an Effective Thermoelectric MaterialADVANCED FUNCTIONAL MATERIALS, Issue 15 2009Sabah K. Bux Abstract Thermoelectric power sources have consistently demonstrated their extraordinary reliability and longevity for deep space missions and small unattended terrestrial systems. However, more efficient bulk materials and practical devices are required to improve existing technology and expand into large-scale waste heat recovery applications. Research has long focused on complex compounds that best combine the electrical properties of degenerate semiconductors with the low thermal conductivity of glassy materials. Recently it has been found that nanostructuring is an effective method to decouple electrical and thermal transport parameters. Dramatic reductions in the lattice thermal conductivity are achieved by nanostructuring bulk silicon with limited degradation in its electron mobility, leading to an unprecedented increase by a factor of 3.5 in its performance over that of the parent single-crystal material. This makes nanostructured bulk (nano-bulk) Si an effective high temperature thermoelectric material that performs at about 70% the level of state-of-the-art Si0.8Ge0.2 but without the need for expensive and rare Ge. [source] Marine range shifts and species introductions: comparative spread rates and community impactsGLOBAL ECOLOGY, Issue 3 2010Cascade J. B. Sorte ABSTRACT Aim, Shifts in species ranges are a predicted and realized effect of global climate change; however, few studies have addressed the rates and consequence of such shifts, particularly in marine systems. Given ecological similarities between shifting and introduced species, we examined how our understanding of range shifts may be informed by the more established study of non-native species introductions. Location, Marine systems world-wide. Methods, Database and citation searches were used to identify 129 marine species experiencing range shifts and to determine spread rates and impacts on recipient communities. Analyses of spread rates were based on studies for which post-establishment spread was reported in linear distance. The sizes of the effects of community impacts of shifting species were compared with those of functionally similar introduced species having ecologically similar impacts. Results, Our review and meta-analyses revealed that: (1) 75% of the range shifts found through the database search were in the poleward direction, consistent with climate change scenarios, (2) spread rates of range shifts were lower than those of introductions, (3) shifting species spread over an order of magnitude faster in marine than in terrestrial systems, and (4) directions of community effects were largely negative and magnitudes were often similar for shifters and introduced species; however, this comparison was limited by few data for range-shifting species. Main conclusions, Although marine range shifts are likely to proceed more slowly than marine introductions, the community-level effects could be as great, and in the same direction, as those of introduced species. Because it is well-established that introduced species are a primary threat to global biodiversity, it follows that, just like introductions, range shifts have the potential to seriously affect biological systems. In addition, given that ranges shift faster in marine than terrestrial environments, marine communities might be affected faster than terrestrial ones as species shift with climate change. Regardless of habitat, consideration of range shifts in the context of invasion biology can improve our understanding of what to expect from climate change-driven shifts as well as provide tools for formal assessment of risks to community structure and function. [source] Patch occupancy of North American mammals: is patchiness in the eye of the beholder?JOURNAL OF BIOGEOGRAPHY, Issue 8 2003Robert K. Swihart Abstract Aim Intraspecific variation in patch occupancy often is related to physical features of a landscape, such as the amount and distribution of habitat. However, communities occupying patchy environments typically exhibit non-random distributions in which local assemblages of species-poor patches are nested subsets of assemblages occupying more species-rich patches. Nestedness of local communities implies interspecific differences in sensitivity to patchiness. Several hypotheses have been proposed to explain interspecific variation in responses to patchiness within a community, including differences in (1) colonization ability, (2) extinction proneness, (3) tolerance to disturbance, (4) sociality and (5) level of adaptation to prevailing environmental conditions. We used data on North American mammals to compare the performance of these ,ecological' hypotheses and the ,physical landscape' hypothesis. We then compared the best of these models against models that scaled landscape structure to ecologically relevant attributes of individual species. Location North America. Methods We analysed data on prevalence (i.e. proportion of patches occupied in a network of patches) and occupancy for 137 species of non-volant mammals and twenty networks consisting of four to seventy-five patches. Insular and terrestrial networks exhibited significantly different mean levels of prevalence and occupancy and thus were analysed separately. Indicator variables at ordinal and family levels were included in models to correct for effects caused by phylogeny. Akaike's information criterion was used in conjunction with ordinary least squares and logistic regression to compare hypotheses. Results A patch network's physical structure, indexed using patch area and isolation, received the greatest support among models predicting the prevalence of species on insular networks. Niche breadth (diet and habitat) received the greatest support for predicting prevalence of species occupying terrestrial networks. For both insular and terrestrial systems, physical features (patch area and isolation) received greater support than any of the ecological hypotheses for predicting species occupancy of individual patches. For terrestrial systems, scaling patch area by its suitability to a focal species and by individual area requirements of the species, and scaling patch isolation by species-specific dispersal ability and niche breadth, resulted in models of patch occupancy that were superior to models relying solely on physical landscape features. For all selected models, unexplained levels of variation were high. Main conclusions Stochasticity dominated the systems we studied, indicating that random events are probably quite important in shaping local communities. With respect to deterministic factors, our results suggest that forces affecting species prevalence and occupancy may differ between insular and terrestrial systems. Physical features of insular systems appeared to swamp ecological differences among species in determining prevalence and occupancy, whereas species with broad niches were disproportionately represented in terrestrial networks. We hypothesize that differential extinction over long time periods in highly variable networks has driven nestedness of mammalian communities on islands, whereas differential colonization over shorter time-scales in more homogeneous networks probably governed the local structure of terrestrial communities. Our results also demonstrate that integration of a species' ecological traits with physical features of a patch network is superior to reliance on either factor separately when attempting to predict the species' probability of patch occupancy in terrestrial systems. [source] Reconciling plant strategy theories of Grime and TilmanJOURNAL OF ECOLOGY, Issue 6 2005JOSEPH M. CRAINE Summary 1The theories of Grime and Tilman are ambitious attempts to unify disparate theories regarding the construction of plants, their interaction with the environment and the assembly of communities. After over two decades of parallel research, their ideas have not been reconciled, hindering progress in understanding the functioning of ecosystems. 2Grime's theories do not adequately incorporate the importance of non-heterogeneous supplies of nutrients and how these supplies are partitioned over long time scales, are inconsistent regarding the importance of disturbance in nutrient-limited habitats and need to reconsider the carbon economy of shade-tolerant plants. 3Failure to account for differences between aquatic and terrestrial systems in how resource supplies are partitioned led Tilman to develop a shifting set of theories that have become reduced in mechanistic detail over time. The most recent highlighted the reduction of nutrient concentrations in soil solution, although it can no longer be derived from any viable mechanistic model. The slow diffusion of nutrients in soils means that the reduction of average soil solution nutrient concentrations cannot explain competitive exclusion. 4Although neither theory, nor a union of the two, adequately characterizes the dynamics of terrestrial plant assemblages, the complementarity in their assumptions serve as an important foundation for future theory and research. 5Reconciling the approaches of Grime and Tilman leads to six scenarios for competition for nutrients and light, with the outcome of each depending on the ability of plants to pre-empt supplies. Under uniform supplies, pulses or patches, light competition requires leaf area dominance, while nutrient competition requires root length dominance. There are still important basic questions regarding the nature of nutrient supplies that will need to be answered, but recent research brings us closer to a unified set of theories on resource competition. [source] Biodiversity effects on ecosystem functioning: emerging issues and their experimental test in aquatic environmentsOIKOS, Issue 3 2004Paul S. Giller Recent experiments, mainly in terrestrial environments, have provided evidence of the functional importance of biodiversity to ecosystem processes and properties. Compared to terrestrial systems, aquatic ecosystems are characterised by greater propagule and material exchange, often steeper physical and chemical gradients, more rapid biological processes and, in marine systems, higher metazoan phylogenetic diversity. These characteristics limit the potential to transfer conclusions derived from terrestrial experiments to aquatic ecosystems whilst at the same time provide opportunities for testing the general validity of hypotheses about effects of biodiversity on ecosystem functioning. Here, we focus on a number of unique features of aquatic experimental systems, propose an expansion to the scope of diversity facets to be considered when assessing the functional consequences of changes in biodiversity and outline a hierarchical classification scheme of ecosystem functions and their corresponding response variables. We then briefly highlight some recent controversial and newly emerging issues relating to biodiversity-ecosystem functioning relationships. Based on lessons learnt from previous experimental and theoretical work, we finally present four novel experimental designs to address largely unresolved questions about biodiversity-ecosystem functioning relationships. These include (1) investigating the effects of non-random species loss through the manipulation of the order and magnitude of such loss using dilution experiments; (2) combining factorial manipulation of diversity in interconnected habitat patches to test the additivity of ecosystem functioning between habitats; (3) disentangling the impact of local processes from the effect of ecosystem openness via factorial manipulation of the rate of recruitment and biodiversity within patches and within an available propagule pool; and (4) addressing how non-random species extinction following sequential exposure to different stressors may affect ecosystem functioning. Implementing these kinds of experimental designs in a variety of systems will, we believe, shift the focus of investigations from a species richness-centred approach to a broader consideration of the multifarious aspects of biodiversity that may well be critical to understanding effects of biodiversity changes on overall ecosystem functioning and to identifying some of the potential underlying mechanisms involved. [source] Short-term differences in animal assemblages in patches formed by loss and growth of habitatAUSTRAL ECOLOGY, Issue 5 2010PETER I. MACREADIE Abstract Ecological theory predicts that habitat growth and loss will have different effects on community structure, even if they produce patches of the same size. Despite this, studies on the effects of patchiness are often performed without prior knowledge of the processes responsible for the patchiness. We manipulated artificial seagrass habitat in temperate Australia to test whether fish and crustacean assemblages differed between habitats that formed via habitat loss and habitat growth. Habitat loss treatments (originally 16 m2) and habitat growth treatments (originally 0 m2) were manipulated over 1 week until each reached a final patch size of 4 m2. At this size, each was compared through time (0,14 days after manipulation) with control patches (4 m2 throughout the experiment). Assemblages differed significantly among treatments at 0 and 1 day after manipulation, with differences between growth and loss treatments contributing to most of the dissimilarity. Immediately after the final manipulation, total abundance in habitat loss treatments was 46% and 62% higher than controls and habitat growth treatments, respectively, which suggests that animals crowded into patches after habitat loss. In contrast to terrestrial systems, crowding effects were brief (,1 day), signifying high connectivity in marine systems. Growth treatments were no different to controls, despite the lower probability of animals encountering patches during the growth phase. Our study shows that habitat growth and loss can cause short-term differences in animal abundance and assemblage structure, even if they produce patches of the same size. [source] Growth, lipid content, productivity, and fatty acid composition of tropical microalgae for scale-up productionBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2010Roger Huerlimann Abstract Biomass and lipid productivity, lipid content, and quantitative and qualitative lipid composition are critical parameters in selecting microalgal species for commercial scale-up production. This study compares lipid content and composition, and lipid and biomass productivity during logarithmic, late logarithmic, and stationary phase of Nannochloropsis sp., Isochrysis sp., Tetraselmis sp., and Rhodomonas sp. grown in L1-, f/2-, and K-medium. Of the tested species, Tetraselmis sp. exhibited a lipid productivity of 3.9,4.8,g,m,2,day,1 in any media type, with comparable lipid productivity by Nannochloropsis sp. and Isochrysis sp. when grown in L1-medium. The dry biomass productivity of Tetraselmis sp. (33.1,45.0,g,m,2,day,1) exceeded that of the other species by a factor 2,10. Of the organisms studied, Tetraselmis sp. had the best dry biomass and/or lipid production profile in large-scale cultures. The present study provides a practical benchmark, which allows comparison of microalgal production systems with different footprints, as well as terrestrial systems. Biotechnol. Bioeng. 2010;107: 245,257. © 2010 Wiley Periodicals, Inc. [source] | ||||||||||