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71.
72.
Jean-Pierre Lechaire Ghislaine Frébourg Françoise Gaill Olivier Gros 《Marine Biology》2008,154(4):693-700
In this study, Codakia orbicularis gill-tissues were cryo-fixed by using high-pressure freezing, a freeze substitution process and finally by cryo-embedding
in Lowicryl. Ultrathin sections were then used for an EFTEM microanalysis. Results show that intracellular bacterial symbionts
contain elemental sulphur in periplasmic vesicles as indicated by conventional TEM. When sulphur is temporarily depleted in
the environment, such structures may act as energy sources for bacterial metabolism. Moreover, sulphate was detected in the
cytoplasm of the bacterial symbionts, suggesting the oxidation of elemental sulphur, located in periplasmic granules, to sulphate
(the final step in sulphur oxidation) by these chemoautotrophic bacteria. To assess the effects of host starvation on the
bacterial sulphur content, adult individuals of C. orbicularis were maintained in starvation for 6 weeks in sterile artificial seawater depleted in sulphur. During starvation, both (1)
the number of bacteria inside the bacteriocytes and (2) the number of periplasmic granules per prokaryotic cell decreased.
The content of the remaining periplasmic granules had been modified to sulphate. This observation suggests that bacterial
gill-endosymbionts used the elemental sulphur in their periplasmic granules as stored substrate for oxidation in order to
produce energy in case of sulphur depletion. 相似文献
73.
Little is known on the factors controlling distribution and abundance of snow petrels in Antarctica. Studying habitat selection through modeling may provide useful information on the relationships between this species and its environment, especially relevant in a climate change context, where habitat availability may change. Validating the predictive capability of habitat selection models with independent data is a vital step in assessing the performance of such models and their potential for predicting species’ distribution in poorly documented areas.From the results of ground surveys conducted in the Casey region (2002–2003, Wilkes Land, East Antarctica), habitat selection models based on a dataset of 4000 nests were created to predict the nesting distribution of snow petrels as a function of topography and substrate. In this study, the Casey models were tested at Mawson, 3800 km away from Casey. The location and characteristics of approximately 7700 snow petrel nests were collected during ground surveys (Summer 2004–2005). Using GIS, predictive maps of nest distribution were produced for the Mawson region with the models derived from the Casey datasets and predictions were compared to the observed data. Models performance was assessed using classification matrixes and Receiver operating characteristic (ROC) curves. Overall correct classification rates for the Casey models varied from 57% to 90%. However, two geomorphologically different sub-regions (coastal islands and inland mountains) were clearly distinguished in terms of habitat selection by Casey model predictions but also by the specific variations in coefficients of terms in new models, derived from the Mawson data sets. Observed variations in the snow petrel aggregations were found to be related to local habitat availability.We discuss the applicability of various types of models (GLM, CT) and investigate the effect of scale on the prediction of snow petrel habitats. While the Casey models created with data collected at the nest scale did not perform well at Mawson due to regional variations in nest micro-characteristics, the predictive performance of models created with data compiled at a coarser scale (habitat units) was satisfactory. Substrate type was the most robust predictor of nest presence between Casey and Mawson. This study demonstrate that it is possible to predict at the large scale the presence of snow petrel nests based on simple predictors such as topography and substrate, which can be obtained from aerial photography. Such methodologies have valuable applications in the management and conservation of this top predator and associated resources and may be applied to other Antarctic, Sub-Antarctic and lower latitudes species and in a variety of habitats. 相似文献
74.
75.
Daniel Ovando Jennifer E. Caselle Christopher Costello Olivier Deschenes Steven D. Gaines Ray Hilborn Owen Liu 《Conservation biology》2021,35(6):1861-1870
Marine protected areas (MPAs) cover 3–7% of the world's ocean, and international organizations call for 30% coverage by 2030. Although numerous studies show that MPAs produce conservation benefits inside their borders, many MPAs are also justified on the grounds that they confer conservation benefits to the connected populations that span beyond their borders. A network of MPAs covering roughly 20% of the Channel Islands National Marine Sanctuary was established in 2003, with a goal of providing regional conservation and fishery benefits. We used a spatially explicit bioeconomic simulation model and a Bayesian difference-in-difference regression to examine the conditions under which MPAs can provide population-level conservation benefits inside and outside their borders and to assess evidence of those benefits in the Channel Islands. As of 2017, we estimated that biomass densities of targeted fin-fish had a median value 81% higher (90% credible interval: 23–148) inside the Channel Island MPAs than outside. However, we found no clear effect of these MPAs on mean total biomass densities at the population level: estimated median effect was –7% (90% credible interval: –31 to 23) from 2015 to 2017. Our simulation model showed that effect sizes of MPAs of <30% were likely to be difficult to detect (even when they were present); smaller effect sizes (which are likely to be common) were even harder to detect. Clearly, communicating expectations and uncertainties around MPAs is critical to ensuring that MPAs are effective. We provide a novel assessment of the population-level effects of a large MPA network across many different species of targeted fin-fish, and our results offer guidance for communities charged with monitoring and adapting MPAs. 相似文献
76.
Ribolzi O Cuny J Sengsoulichanh P Mousquès C Soulileuth B Pierret A Huon S Sengtaheuanghoung O 《Environmental management》2011,47(2):291-302
Improving access to clean water has the potential to make a major contribution toward poverty reduction in rural communities
of Lao P.D.R. This study focuses on stream water quality along a Mekong basin tributary, the Houay Xon that flows within a
mountainous, mosaic land-use catchment of northern Lao P.D.R. To compare direct water quality measurements to the perception
of water quality within the riparian population, our survey included interviews of villagers. Water quality was found to vary
greatly depending on the location along the stream. Overall, it reflected the balance between the stream self-cleaning potential
and human pressure on the riparian zone: (i) high bacteria and suspended load levels occurred where livestock are left to
free-range within the riparian zone; (ii) very low oxygen content and high bacteriological contamination prevailed downstream
from villages; (iii) high concentrations of bacteria were consistently observed along urbanized banks; (iv) low oxygen content
were associated with the discharge of organic-rich wastewater from a small industrial plant; (v) very high suspended load
and bacteria levels occurred during flood events due to soil erosion from steep cultivated hill slopes. Besides these human
induced pollutions we also noted spontaneous enrichments in metals in wetland areas fed by dysoxic groundwater. These biophysical
measurements were in agreement with the opinions expressed by the majority of the interviewees who reported poor and decreasing
water quality in the Houay Xon catchment. Based on our survey, we propose recommendations to improve or maintain stream water
quality in the uplands of northern Lao P.D.R. 相似文献
77.
Both evolutionary ecologists and wildlife managers make inference based on how fitness and demography vary in space. Spatial variation in survival can be difficult to assess in the wild because (1) multisite study designs are not well suited to populations that are continuously distributed across a large area and (2) available statistical models accounting for detectability less than 1.0 do not easily cope with geographical coordinates. Here we use penalized splines within a Bayesian state-space modeling framework to estimate and visualize survival probability in two dimensions. The approach is flexible in that no parametric form for the relationship between survival and coordinates need be specified a priori. To illustrate our method, we study a game species, the Eurasian Woodcock Scolopax rusticola, based on band recovery data (5000 individuals) collected over a > 50 000-km2 area in west-central France with contrasted habitats and hunting pressures. We find that spatial variation in survival probability matches an index of hunting pressure and creates a mosaic of population sources and sinks. Such analyses could provide guidance concerning the spatial management of hunting intensity or could be used to identify pathways of spatial variation in fitness, for example, to study adaptation to changing landscape and climate. 相似文献
78.
. Despite the increased complexity of experimental and theoretical studies on the biodiversity-ecosystem functioning (B-EF) relationship, a major challenge is to demonstrate whether the observed importance of biodiversity in controlled experimental systems also persists in nature. Due to their structural simplicity and their low levels of human impacts, extreme species-poor ecosystems may provide new insights into B-EF relationships in natural systems. We address this issue using shredder invertebrate communities and organic matter decomposition rates in 24 high-altitude (3200-3900 m) Neotropical streams as a study model. We first assessed the effects of stream characteristics and shredder diversity and abundance on organic matter decomposition rates in coarse- and fine-mesh bags. We found the interaction term shredder richness x shredder abundance had the most significant impact on decomposition rates in the field, although water discharge may also play a role locally. We also examined the relative contribution of the three most abundant shredders on decomposition rates by manipulating shredder richness and community composition in a field experiment. Transgressive overyielding was detected among the three shredder species, indicating complementary resource use and/or facilitation. By integrating survey and experimental data in surface response analyses we found that observed B-EF patterns fit those predicted by a linear model that described litter decomposition rates as a function of increasing shredder richness and the relative abundance of the most efficient shredders. Finally, the validity of our approach was tested in a broader context by using two independent but comparable data sets from 49 French and Swedish streams showing more complex shredder community structure. Results revealed that richness and identity effects on decomposition rates were lost with increasing shredder community complexity. Our approach of combining experimental and empirical data with modeling in species-poor ecosystems may serve as an impetus for new B-EF studies. If theory can explain B-EF in low-diversity ecosystems, it may also have credibility in more complex ones. 相似文献
79.
Pourcelot L Boulet B Le Corre C de Vismes Ott A Cagnat X Loyen J Fayolle C Van Hecke W Martinez B Petit J Kaltenmeier R Gieré R 《Journal of environmental monitoring : JEM》2011,13(5):1327-1336
Cypress needles collected at the edge of the Malvési uranium facility (SW France) exhibit enhanced activities of actinides and some decay products (uranium, americium, plutonium, (230)Th, (226)Ra) compared to a remote site. These enhanced activities resulted from the release of U via smokestacks and passive release from former artificial ponds located inside the nuclear site. Enhanced activities are also observed in selected produce (wheat, lettuce, fruits) sampled from the edge of the site. However, excess actinides measured in wheat grains in 2007 are inconsistent with the activities and the uranium ratio measured in the soils. This result suggests that the studied annual crops were contaminated mainly through the short-term release of airborne actinides, and that other transfer pathways, such as, uptake through the roots or adhesion of soil particles, were negligible. 相似文献
80.
Guillaume Péron Yves Ferrand François Gossmann Claudine Bastat Michel Guénézan Olivier Gimenez 《Behavioral ecology and sociobiology》2011,65(10):1949-1955
During unpredictable adverse conditions, endotherms can engage in emergency behaviors (movement, torpor, hyperphagia) to maintain
energy balance and reduce mortality hazards. Bird “escape migration” is one of the most visible of these behaviors. In this
study, we focus on a Eurasian Woodcock Scolopax rusticola population. Seasonal migrations bring this population from its breeding grounds in Eastern and Northern Europe to its wintering
grounds in France. A varying number of these birds are also regularly reported from Spain, supposedly during additional escape
movements that occur in winter. Using models that account for the imperfect detection rate of individuals and a large (>44,000
individuals) dataset combining information from the wintering and breeding ranges, we show that severe winters significantly
reduced survival probability, but that migration to Spain increased only during the most intense cold spell that occurred
over the 20-year study period. This suggests that the decision to resume migration during the winter is submitted to a threshold
mechanism, which we discuss in the light of current models of migratory behavior. 相似文献