Disentangling the effects of local and regional factors on the thermal tolerance of freshwater crustaceans

In the global warming context, we compared the thermal tolerance of several populations of the crustacean Gammarus pulex (Amphipoda: Gammaridae) along a latitudinal thermal gradient in the Rh?ne Valley. To disentangle the effect of regional (North vs. South) and local (site-specific) factors, the ecophysiological responses of populations were investigated at two levels of biological organisation: whole organism level considering body size [critical thermal maximum (CTmax), mean speed of locomotion (MS), time mobile (TM)] and organelle function level [mitochondrial respiratory control ratios (RCRs)]. CTmax and RCRs, but not MS and TM, revealed a significantly higher thermal tolerance in southern populations compared to northern ones. Nevertheless, temperatures ≥ 30°C were deleterious for all populations, suggesting that populations located in the warmer limit of the species distribution will be more threatened by climate change as they live closer to their upper thermal limits. The strong differences observed between populations indicate that the species-level thermal tolerance used in predictive models may not be informative enough to study the impact of global warming on species distributions. This work also reveals that an appropriate choice of indicators is essential to study the consequences of global warming since the response of organisms at the whole body level can be influenced by local conditions.     

Factors affecting information transfer from knowledgeable to naive individuals in groups

There is evidence that individuals in animal groups benefit from the presence of knowledgeable group members in different ways. Experiments and computer simulations have shown that a few individuals within a group can lead others, for a precise task and at a specific moment. As a group travels, different individuals possessing a particular knowledge may act as temporary leaders, so that the group will, as a whole, follow their behaviour. In this paper, we use a model to study different factors influencing group response to temporary leadership. The model is based on four individual behaviours. Three of those, attraction, repulsion, and alignment, are shared by all individuals. The last one, attraction toward the source of a stimulus, concerns only a fraction of the group members. We explore the influence of group size, proportion of stimulated individuals, number of influential neighbours, and intensity of the attraction to the source of the stimulus, on the proportion of the group reaching this source. Special attention is given to the simulation of large group size, close to those observed in nature. Groups of 100, 400 and 900 individuals are currently simulated, and up to 8,000 in one experiment. We show that more stimulated individuals and a larger group size both induce the arrival of a larger fraction of the group. The number of influential neighbours and the intensity of the stimulus have a non-linear influence on the proportion of the group arrival, displaying first a positive relationship and then, above a given threshold, a negative one. We conclude that an intermediate level of group cohesion provides optimal transfer information from knowledgeable to naive individuals.     

Measurement of metal bioaccessibility in vegetables to improve human exposure assessments: field study of soil–plant–atmosphere transfers in urban areas,South China

The quality of cultivated consumed vegetables in relation to environmental pollution is a crucial issue for urban and peri-urban areas, which host the majority of people at the global scale. In order to evaluate the fate of metals in urban soil–plant–atmosphere systems and their consequences on human exposure, a field study was conducted at two different sites near a waste incinerator (site A) and a highway (site B). Metal concentrations were measured in the soil, settled atmospheric particulate matter (PM) and vegetables. A risk assessment was performed using both total and bioaccessible metal concentrations in vegetables. Total metal concentrations in PM were (mg kg^?1): (site A) 417 Cr, 354 Cu, 931 Zn, 6.3 Cd and 168 Pb; (site B) 145 Cr, 444 Cu, 3289 Zn, 2.9 Cd and 396 Pb. Several total soil Cd and Pb concentrations exceeded China’s Environmental Quality Standards. At both sites, there was significant metal enrichment from the atmosphere to the leafy vegetables (correlation between Pb concentrations in PM and leaves: r = 0.52, p < 0.05) which depended on the plant species. Total Cr, Cd and Pb concentrations in vegetables were therefore above or just under the maximum limit levels for foodstuffs according to Chinese and European Commission regulations. High metal bioaccessibility in the vegetables (60–79 %, with maximum value for Cd) was also observed. The bioaccessible hazard index was only above 1 for site B, due to moderate Pb and Cd pollution from the highway. In contrast, site A was considered as relatively safe for urban agriculture.     

Hunting, law enforcement, and African primate conservation

Abstract: Primates are regularly hunted for bushmeat in tropical forests, and systematic ecological monitoring can help determine the effect hunting has on these and other hunted species. Monitoring can also be used to inform law enforcement and managers of where hunting is concentrated. We evaluated the effects of law enforcement informed by monitoring data on density and spatial distribution of 8 monkey species in Taï National Park, Côte d’Ivoire. We conducted intensive surveys of monkeys and looked for signs of human activity throughout the park. We also gathered information on the activities of law‐enforcement personnel related to hunting and evaluated the relative effects of hunting, forest cover and proximity to rivers, and conservation effort on primate distribution and density. The effects of hunting on monkeys varied among species. Red colobus monkeys (Procolobus badius) were most affected and Campbell's monkeys (Cercopithecus campbelli) were least affected by hunting. Density of monkeys irrespective of species was up to 100 times higher near a research station and tourism site in the southwestern section of the park, where there is little hunting, than in the southeastern part of the park. The results of our monitoring guided law‐enforcement patrols toward zones with the most hunting activity. Such systematic coordination of ecological monitoring and law enforcement may be applicable at other sites.     

COSMOS,a spatially explicit model to simulate the epidemiology of Cosmopolites sordidus in banana fields

A stochastic individual-based model called COSMOS was developed to simulate the epidemiology of banana weevil Cosmopolites sordidus, a major pest of banana fields. The model is based on simple rules of local movement of adults, egg laying of females, development and mortality, and infestation of larvae inside the banana plants. The biological parameters were estimated from the literature, and the model was validated at the small-plot scale. Simulated and observed distributions of attacks were similar except for five plots out of 18, using a Kolmogorov–Smirnov test. These exceptions may be explained by variation in predation of eggs and measurement error. An exhaustive sensitivity analysis using the Morris method showed that predation rate of eggs, demographic parameters of adults and mortality rate of larvae were the most influential parameters. COSMOS was therefore used to test different spatial arrangements of banana plants on the epidemiology of C. sordidus. Planting bananas in groups increased the time required to colonise plots but also the percentage of banana plants with severe attacks. Spatial heterogeneity of banana stages had no effect on time required to colonise plots but increased the mean level of attacks. Our model helps explain key factors of population dynamics and the epidemiology of this tropical pest.     

Removal of polycyclic aromatic hydrocarbons from aged-contaminated soil using cyclodextrins: experimental study

The removal of polycyclic aromatic hydrocarbons (PAHs) from soil using water as flushing agent is relatively ineffective due to their low aqueous solubility. However, addition of cyclodextrin (CD) in washing solutions has been shown to increase the removal efficiency several times. Herein are investigated the effectiveness of cyclodextrin to remove PAH occurring in industrially aged-contaminated soil. Beta-cyclodextrin (BCD), hydroxypropyl-beta-cyclodextrin (HPCD) and methyl-beta-cyclodextrin (MCD) solutions were used for soil flushing in column test to evaluate some influent parameters that can significantly increase the removal efficiency. The process parameters chosen were CD concentration, ratio of washing solution volume to soil weight, and temperature of washing solution. These parameters were found to have a significant and almost linear effect on PAH removal from the contaminated soil, except the temperature where no significant enhancement in PAH extraction was observed for temperature range from 5 to 35 degrees C. The PAHs extraction enhancement factor compared to water was about 200.     

Heavy metal contamination from mining sites in South Morocco: 2. Assessment of metal accumulation and toxicity in plants

Metalliferous soils cover a relatively large surface area in Morocco, and up to now no hyperaccumulating plants have been identified on these mining or these industrial sites. The aim of this work was to assess the extent of metal accumulation by plants found in three mining areas in southern Morocco with the ultimate goal of finding metal hyperaccumulating species by using the MetPAD biotest. The biotest helps to obtain information on the selective metal toxicity of aqueous extracts from the plants. A strong metal toxicity, as revealed by the biotest is an indication of a hyperaccumulating plant. Toxicity tests were run concurrently with chemicals analyses of metals in plants and their water extracts. The chemical analyses allow the determination of the hyperaccumulated metal(s). Specimens of the plant species mainly growing on and in the vicinity of the three mines were sampled with their corresponding soils. The results show that all plants analyzed had lower heavy metal content and toxicity despite the relatively very high soil concentrations. A comparison of our results with the criterion used to classify the hyperaccumulator plants indicates that plants we collected from mining sites were hypertolerant but not hyperaccumulators. This was confirmed by transfer factors generally lower than 1. Nevertheless, these tolerant plants species can be used as tools for revegetation for erosion control in metals-contaminated sites (phytostabilization).     

Basic principles and ecological consequences of changing water regimes on nitrogen cycling in fluvial systems

Understanding the environmental consequences of changing water regimes is a daunting challenge for both resource managers and ecologists. Balancing human demands for fresh water with the needs of the environment for water in appropriate amounts and at the appropriate times are shaping the ways by which this natural resource will be used in the future. Based on past decisions that have rendered many freshwater resources unsuitable for use, we argue that river systems have a fundamental need for appropriate amounts and timing of water to maintain their biophysical integrity. Biophysical integrity is fundamental for the formulation of future sustainable management strategies. This article addresses three basic ecological principles driving the biogeochemical cycle of nitrogen in river systems. These are (1) how the mode of nitrogen delivery affects river ecosystem functioning, (2) how increasing contact between water and soil or sediment increases nitrogen retention and processing, and (3) the role of floods and droughts as important natural events that strongly influence pathways of nitrogen cycling in fluvial systems. New challenges related to the cumulative impact of water regime change, the scale of appraisal of these impacts, and the determination of the impacts due to natural and human changes are discussed. It is suggested that cost of long-term and long-distance cumulative impacts of hydrological changes should be evaluated against short-term economic benefits to determine the real environmental costs.     

Reactive transport of 85Sr in a chernobyl sand column: static and dynamic experiments and modeling

The effects of nonlinear sorption and competition with major cations present in the soil solution on radioactive strontium transport in an eolian sand were examined. Three laboratory techniques were used to identify and quantify the chemical and hydrodynamic processes involved in strontium transport: batch experiments, stirred flow-through reactor experiments and saturated laboratory columns. The major goal was to compare the results obtained under static and dynamic conditions and to describe in a deterministic manner the predominant processes involved in radioactive strontium transport in such systems. Experiments under dynamic conditions, namely flow-through reactor and column experiments, were in very good agreement even though the solid/liquid ratio was very different. The experimental data obtained from the flow-through reactor study pointed to a nonlinear, instantaneous and reversible sorption process. Miscible displacement experiments were conducted to demonstrate the competition between stable and radioactive strontium and to quantify its effect on the 85Sr retardation factor. The results were modeled using the PHREEQC computer code. A suitable cation-exchange model was used to describe the solute/soil reaction. The model successfully described the results of the entire set of miscible displacement experiments using the same set of parameter values for the reaction calculations. The column study revealed that the stable Sr aqueous concentration was the most sensitive variable of the model, and that the initial state of the sand/solution system had also to be controlled to explain and describe the measured retardation factor of radioactive strontium. From these observations, propositions can be made to explain the discrepancies observed between some data obtained from static (batches) and dynamic (reactor and column) experiments. Desorbed antecedent species (stable Sr) are removed from the column or reactor in the flow system but continue to compete for sorption sites in the batch system. Batch experiments are simple and fast, and provide a very useful means of multiplying data. However, interpretation becomes difficult when different species compete for sorption sites in the soil/solution system. A combination of batches, flow-through reactor and column experiments, coupled with hydrogeochemical modeling, would seem to offer a very powerful tool for identifying and quantifying the predominant processes on a cubic decimeter scale (dm3) and for providing a range of radioactive strontium retardation factor as a function of the geochemistry of the soil/solution system.