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441.
Eric Lichtfouse Michel Lichtfouse Michaele Kashgarian Roland Bol 《Environmental Chemistry Letters》2005,3(2):78-81
Measuring the amount of fossil fuel carbon stored in the vegetation is now crucial to understand the mechanisms ruling climate
changes. In this respect, highly polluted areas such as major towns represent “natural” laboratories because fossil fuel CO2 (14C-free) is isotopically distinct from mean atmospheric CO2 (14C-labeled). Here, a14C study of urban grasses near a major highway in Paris, France, shows that plants store up to 13% of fossil fuel carbon. The
14C composition of urban grasses is thus a novel parameter to assess the fossil fuel CO2 pollution. 相似文献
442.
443.
Patrice Lucchetta Emmanuel Desouhant Eric Wajnberg Carlos Bernstein 《Behavioral ecology and sociobiology》2007,61(9):1409-1418
The reproductive success of insect parasitoids depends on two activities, searching for hosts to obtain immediate fitness
rewards (offspring) and searching for food to extend life span and enhance future reproductive opportunities. Models suggest
that to deal with this trade-off and to cope with the variability of the resources they depend on, parasitoids should simultaneously
integrate information originating from three distinct sources: host and food availabilities in the environment (environmental
information) and the metabolic reserves of the parasitoid (internal information). We tested whether, in the parasitic wasp
Venturia canescens, these three types of information are perceived simultaneously and interact during host-patch exploitation. Experiments were
performed with strains originating from two different geographical locations and with individuals of the two reproductive
modes, arrhenotoky and thelytoky. We hypothesised that there would be differences between modes of reproduction as they thrive
in different ecological conditions. Our results show that metabolic state, food availability and the number of ovipositions
performed simultaneously modulate patch residence time in V. canescens of both populations and reproductive modes. Unfed wasps left their host patch earlier than fed ones. The tendency to leave
the patch increased with an increasing probability of finding food. Our study confirms that globally, each oviposition increases
the patch-leaving tendency (decremental mechanism). This effect was modulated by both the metabolic reserves and food availability,
and the relationship depended on the geographic origin of populations. Individuals of one of the populations switched from
a decremental to an incremental patch-leaving mechanism depending on the presence or absence of food in the vicinity. Differences
between reproductive modes in the responses to environmental cues can be explained by the different ecological conditions
they live in. 相似文献
444.
Eric J Bergman Robert A Garrott Scott Creel John J Borkowski Rosemary Jaffe E G R Watson 《Ecological applications》2006,16(1):273-284
Within predator-prey systems behavior can heavily influence spatial dynamics, and accordingly, the theoretical study of how spatial dynamics relate to stability within these systems has a rich history. However, our understanding of these behaviors in large mammalian systems is poorly developed. To address the relationship between predator selection patterns, prey density, and prey vulnerability, we quantified selection patterns for two fine-scale behaviors of a recovering wolf (Canis lupus) population in Yellowstone National Park, Wyoming, USA. Wolf spatial data were collected between November and May from 1998-1999 until 2001-2002. Over four winters, 244 aerial locations, 522 ground-based telemetry locations, 1287 km of movement data from snow tracking, and the locations of 279 wolf kill sites were recorded. There was evidence that elk (Cervus elaphus) and bison (Bison bison) densities had a weak effect on the sites where wolves traveled and made kills. Wolf movements showed a strong selection for geothermal areas, meadows, and areas near various types of habitat edges. Proximity to edge and habitat class also had a strong influence on the locations where elk were most vulnerable to predation. There was little evidence that wolf kill sites differed from the places where wolves traveled, indicating that elk vulnerability influenced where wolves selected to travel. Our results indicate that elk are more vulnerable to wolves under certain conditions and that wolves are capable of selecting for these conditions. As such, vulnerability plays a central role in predator-prey behavioral games and can potentially impact the systems to which they relate. 相似文献
445.
Doucet FJ Lead JR Maguire L Achterberg EP Millward GE 《Journal of environmental monitoring : JEM》2005,7(2):115-121
The applicability of environmental scanning electron microscopy (ESEM; imaging of hydrated samples) and conventional high vacuum scanning electron microscopy (SEM; imaging of dried samples at high vacuum) for the observation of natural aquatic colloids and particles was explored and compared. Specific attention was given to the advantages and limitations of these two techniques when used to assess the sizes and morphologies of complex and heterogeneous environmental systems. The observation of specimens using SEM involved drying and coating, whereas ESEM permitted their examination in hydrated form without prior sample preparation or conductive coating. The two techniques provided significantly different micrographs of the same sample. SEM provided sharper images, lower resolution limits (10 nm or lower), but more densely packed particles, suggesting aggregation, and different morphological features than ESEM, suggesting artefacts due to drying. ESEM produced less easily visualised materials, more complex interpretation, slightly higher resolution limits (30-50 nm), but these limitations were more than compensated for by the fact that ESEM samples retained, at least to some extent, their morphological integrity. The results in this paper show that SEM and ESEM should be regarded as complementary techniques for the study of aquatic colloids and particles and that ESEM should be more widely applied to aquatic environmental systems than hitherto. 相似文献
446.
Sylvie Tambutté Eric Tambutté Didier Zoccola Natacha Caminiti Severine Lotto Aurélie Moya Denis Allemand Jess Adkins 《Marine Biology》2007,151(1):71-83
In zooxanthellate corals, the photosynthetic fixation of carbon dioxide and the precipitation of CaCO3 are intimately linked both spatially and temporally making it difficult to study carbon transport mechanisms involved in each
pathway. When studying Tubastrea aurea, a coral devoid of zooxanthellae, we can focus on carbon transport mechanisms involved only in the calcification process.
We performed this study to characterize T. aurea carbonic anhydrase and to determine its role in the calcification process. We have shown that inhibition of tissular carbonic
anhydrase activity affects the calcification rate. We have measured the activity of this enzyme both in the tissues and in
the organix matrix extracted from the skeleton. Our results indicate that organic matrix proteins, which are synthesized by
the calcifying tissues, are not only structural proteins, but they also play a crucial catalytic role by eliminating the kinetic
barrier to interconversion of inorganic carbon at the calcification site. By immunochemistry we have demonstrated the presence
of a protein both in the tissues and in the organic matrix, which shares common features with prokaryotic carbonic anhydrases. 相似文献
447.
Alan J Krupnick Wallace E Oates Eric Van De Verg 《Journal of Environmental Economics and Management》1983,10(3):233-247
After examining the properties of several alternative forms of marketable permit systems for the control of air pollution, this paper proposes a system of pollution offsets as the most promising approach. Under the pollution-offset scheme, sources of emissions are free to trade emissions permits subject to the constraint of no violations of the predetermined air-quality standard at any receptor point. The paper shows that the pollution-offset system has the capacity to achieve the predetermined standards of air quality at the minimum aggregate abatement cost, while making comparatively modest demands both on the sources and on the administering agency. 相似文献
448.
Yannick Outreman Anne Le Ralec Eric Wajnberg Jean-Sébastien Pierre 《Behavioral ecology and sociobiology》2005,58(2):208-217
The present study aimed to address how an insect parasitoid makes patch-departure decisions from various types of host patches and how previous patch experiences in the environment modify this decision-making process. Experiments were done with the parasitic wasp Aphidius rhopalosiphi attacking the grain aphid Sitobion avenae. In the experiments, wasps were observed in a laboratory environment containing several patches of various host densities, and behavioural records were analysed using a Coxs proportional hazards model. Consideration of the effect of the within-patch experience gave a classic pattern of patch-leaving decision rules in parasitoids: A. rhopalosiphi used local information on host quality (i.e. numbers of ovipositions or rejections) and availability (i.e. patch density) to determine departure decision. However, consideration of previous patch experiences provided evidence that these departure rules are fundamentally dynamic, responding to the physiological state of the animal and the information it has about its environment. Results showed that A. rhopalosiphi decreased its tendency to leave the visited patch after an oviposition. However, when a female has already laid several other eggs in the environment, such an incremental mechanism gradually switched to a decremental one. Hence, A. rhopalosiphi responded to egg-load depletion by leaving the visited patches sooner and by depositing a smaller number of eggs in those patches, which probably led to a decreased level of superparasitism. Results also indicated that previous experiences enabled wasps to estimate spatial host distribution and then to adjust their behavioural decisions accordingly. Thus, A. rhopalosiphi was shown to adjust its patch residence time according to the quality and the number of the patches previously visited. These proximate mechanistic rules adopted by A. rhopalosiphi females are discussed in the context of general predictions from optimality models.Communicated by D. Gwynne 相似文献
449.
Serum concentrations of perfluorooctanesulfonate and other fluorochemicals in an elderly population from Seattle, Washington 总被引:14,自引:0,他引:14
Olsen GW Church TR Larson EB van Belle G Lundberg JK Hansen KJ Burris JM Mandel JH Zobel LR 《Chemosphere》2004,54(11):1599-1611
Perfluorooctanesulfonyl fluoride (POSF, C8F17SO2F) related-materials have been used as surfactants, paper and packaging treatments, and surface (e.g., carpet, textile, upholstery) protectants. A metabolite, perfluorooctanesulfonate (PFOS, C8F17SO3−), has been identified in the serum and liver of non-occupationally exposed humans and wildlife. Because of its persistence, an important question was whether elderly humans might have higher PFOS concentrations. From a prospective study designed to examine cognitive function in the Seattle (WA) metropolitan area, blood samples were collected from 238 dementia-free subjects (ages 65–96). High-pressure liquid chromatography-electrospray tandem mass spectrometry determined seven fluorochemicals: PFOS; N-ethyl perfluorooctanesulfonamidoacetate; N-methyl perfluorooctanesulfonamidoacetate; perfluorooctanesulfonamidoacetate; perfluorooctanesulfonamide; perfluorooctanoate; and perfluorohexanesulfonate. Serum PFOS concentrations ranged from less than the lower limit of quantitation (3.4 ppb) to 175.0 ppb (geometric mean 31.0 ppb; 95% CI 28.8–33.4). An estimate of the 95% tolerance limit was 84.1 ppb (upper 95% confidence limit 104.0 ppb). Serum PFOS concentrations were slightly lower among the most elderly. There were no significant differences by sex or years residence in Seattle. The distributions of the other fluorochemicals were approximately an order of magnitude lower. Similar to other reported findings of younger adults, the geometric mean serum PFOS concentration in non-occupational adult populations likely approximates 30–40 ppb with 95% of the population’s serum PFOS concentrations below 100 ppb. 相似文献
450.
Invasibility of Species-Rich Communities in Riparian Zones 总被引:27,自引:0,他引:27
Anne-Marie Planty-Tabacchi Eric Tabacchi Robert J. Naiman Collette Deferrari Henri Décamps 《Conservation biology》1996,10(2):598-607
Invasibility of riparian plant communities was estimated by the percentage of alien species found along the Adour River (Southwest France) and along Lockout Creek, McKenzie River, and Willamette River (Central Cascades, Oregon, U.S.A.). At the patch scale, the invasibilities of riparian plant communities were compared between one exceptionally rich site of the Adour River and patches selected in the Hoh and Dungeness watersheds (Olympic Peninsula, Washington, U.S.A.). Alien species represented 24% of 1396 species for the Adour and 30% of 851 species for the McKenzie. They represented 24% of 148 species for the Hoh drainage and 28% of 200 species for the Dungeness drainage. Similar trends were found along the Adour River and along the McKenzie River for changes in total number of species per site and in percentages of alien species per site. These trends may be related to the intermediate disturbance regimes and to the physical structure of the riparian corridors. Climatic and human factors are also involved in these longitudinal changes. Positive linear relationships were found between the total number of species and the percentage of aliens observed in each site. At the patch scale, most of the sampled communities contained alien species. Although mature vegetative patches appeared to be invasible, young communities contained more alien species than older ones. For entire corridors, a positive linear relationship was found between total species richness and percentage of alien species in each patch type for the richest site of the Adour River. This may be partially explained by landscape features considered in a successional context. We suggest the use of empirical rules, and stress the importance of riparian systems for monitoring the conservation of local and regional species pools are suggested. 相似文献