On metapopulation resistance to drift and extinction

The spatial configuration of metapopulations (numbers, sizes, and localization of patches) affects their ability to resist demographic extinction and genetic drift, but sometimes with opposite effects. Small and isolated patches, for instance, contribute marginally to demography but may play a large role in genetics by maintaining a sizeable amount of genetic variance among demes. In source-sink systems, similarly, connectivity may be beneficial in terms of effective size, but detrimental in terms of survival, by lowering the reproductive value of source populations. How to reconcile these opposite effects? Here we propose an analytical framework that integrates fixation time (ability to resist genetic drift) and extinction time (ability to resist demographic extinction) into a single index of resistance, measuring the ability of a metapopulation to maintain its demo-genetic integrity. We then illustrate with numerical examples how conflicting demands may be resolved.     

Mass effects mediate coexistence in competing shrews

Recent developments in metacommunity theory have raised awareness that processes occurring at regional scales might interfere with local dynamics and affect conditions for the local coexistence of competing species. Four main paradigms are recognized in this context (namely, neutral, patch-dynamics, species-sorting, and mass-effect), which differ according to the role assigned to ecological or life-history differences among competing species, as well as to the relative time scale of regional vs. local dynamics. We investigated the patterns of regional and local coexistence of two species of shrews (Crocidura russula and Sorex coronatus) sharing a similar diet (generalist insectivores) over four generations, in a spatially structured habitat at the altitudinal limit of their distributions. Local populations were small, and regional dynamics were strong, with high rates of extinction and recolonization. Niche analysis revealed significant habitat differentiation on a few important variables, including temperature and availability of winter resting sites. In sites suitable for both species, we found instances of local coexistence with no evidence of competitive exclusion. Patterns of temporal succession did not differ from random, with no suggestion of a colonization-competition trade-off. Altogether, our data provide support for the mass-effect paradigm, where regional coexistence is mediated by specialization on different habitat types, and local coexistence by rescue effects from source sites. The strong regional dynamics and demographic stochasticity, together with high dispersal rates, presumably contributed to mass effects by overriding local differences in specific competitive abilities.     

Implication of two in-stream processes in the fate of nutrients discharged by sewage system into a temporary river

The aim of this study was to better understand the fate of nutrients discharged by sewage treatment plants into an intermittent Mediterranean river, during a low-flow period. Many pollutants stored in the riverbed during the low-flow period can be transferred to the downstream environments during flood events. The study focused on two processes that affect the fate and the transport of nutrients, a physical process (retention in the riverbed sediments) and a biological process (denitrification). A spatial campaign was carried out during a low-flow period to characterize the nutrient contents of both water and sediments in the Vène River. The results showed high nutrient concentrations in the water column downstream of the treated wastewater disposal (up to 13,315 μg N/L for ammonium and 2,901 μg P/L for total phosphorus). Nutrient concentrations decreased rapidly downstream of the disposal whereas nutrient contents in the sediments increased (up to 1,898 and 784 μg/g for total phosphorus and Kjeldahl nitrogen, respectively). According to an in situ experiment using sediment boxes placed in the riverbed for 85 days, we estimated that the proportion of nutrients trapped in the sediments represents 25% (respectively 10%) of phosphorus (respectively nitrogen) loads lost from the water column. In parallel, laboratory tests indicated that denitrification occurred in the Vène River, and we estimated that denitrification likely coupled to nitrification processes during the 85 days of the experiment was significantly involved in the removal of nitrogen loads (up to 38%) from the water column and was greater than accumulation processes.     

When solids meet solids: A glimpse into dust mixture explosions

Mixing an inert solid or a less flammable compound with a combustible dust can be regarded as a direct application of the inherent safety principle of moderation. An experimental investigation was carried out to determine the evolution of the ignition sensitivity and the explosion severity of such various mixtures as a function of their compositions. It demonstrates that the introduction of small amounts of highly combustible powders (such as sulphur or nicotinic acid) to a less flammable dust (such as microcrystalline cellulose or carbon black) can strongly influence the ignition sensitivity as well as the explosion severity.It has notably been shown that the ignition sensitivity of solid/solid mixtures significantly rises up when only 10–5%wt. of highly flammable dust is introduced. Simple models can often be applied to estimate the minimum ignition energy, minimum ignition temperature and minimum explosive concentration of such mixtures. Concerning the dust explosivity, three cases have been studied: mixtures of combustibles dusts without reaction, dusts with reactions between the powders, combustible dusts with inert solid. If the evolution of the maximum explosion pressure can be estimated by using thermodynamic calculations, the maximum rate of pressure rise is more difficult to predict with simple models, and both combustion kinetics and hydrodynamics of the dust clouds should be taken into account. These results were also extended to flammable dust/solid inertant mixture. They clearly show that the concentration of solid inertant at which the ignition is not observed anymore could reach 95%wt. As a consequence, the common recommendation of solid inertant introduction up to 50–80%wt. to prevent dust explosion/ignition should be reconsidered.     

ANN OUTPUT UPDATING OF LUMPED CONCEPTUAL RAINFALL/RUNOFF FORECASTING MODELS1

ABSTRACT: Artificial neural networks (ANNs) are tested for the output updating of one‐day‐ahead and three‐day‐ahead streamflow forecasts derived from three lumped conceptual rainfall/runoff (R‐R) models: the GR4J, the IHAC, and the TOPMO. ANN output updating proved superior to a parameter updating scheme and to the ‘simple’ output updating scheme, which always replicates the last observed forecast error. In fact, ANN output updating was able to compensate for large differences in the initial performance of the three tested lumped conceptual R‐R models, which the other tested updating approaches were not able to achieve. This is done mainly by incorporating input vectors usually exploited for ANN R‐R modeling such as previous rainfall and streamflow observations, in addition to the previous observed error. For one‐day‐ahead forecasts, the performance of all three lumped conceptual R‐R models, used in conjunction with ANN output updating, was equivalent to that of the ANN R‐R model. For three‐day‐ahead forecasts, the performance of the ANN‐output‐updated conceptual models was even superior to that of the ANN R‐R model, revealing that the conceptual models are probably performing some tasks that the ANN R‐R model cannot map. However, further testing is needed to substantiate the last statement.     

Ecological metrics of biomass removed by three methods of purse-seine fishing for tunas in the eastern tropical Pacific Ocean

An ecosystem approach to fisheries management is a widely recognized goal, but describing and measuring the effects of a fishery on an ecosystem is difficult. Ecological information on the entire catch (all animals removed, whether retained or discarded) of both species targeted by the fishery and nontarget species (i.e., bycatch) is required. We used data from the well-documented purse-seine fishery for tunas (Thunnus albacares, T. obesus, and Katsuwonus pelamis) in the eastern tropical Pacific Ocean to examine the fishery's ecological effects. Purse-seine fishing in the eastern tropical Pacific is conducted in 3 ways that differ in the amount and composition of target species and bycatch. The choice of method depends on whether the tunas are swimming alone (unassociated sets), associated with dolphins (dolphin sets), or associated with floating objects (floating-object sets). Among the fishing methods, we compared catch on the basis of weight, number of individuals, trophic level, replacement time, and diversity. Floating-object sets removed 2-3 times as much biomass as the other 2 methods, depending on how removal was measured. Results of previous studies suggest the ecological effects of floating-object sets are thousands of times greater than the effects of other methods, but these results were derived from only numbers of discarded animals. Management of the fishery has been driven to a substantial extent by a focus on reducing bycatch, although discards are currently 4.8% of total catch by weight, compared with global averages of 7.5% for tuna longline fishing and 30.0% for midwater trawling. An ecosystem approach to fisheries management requires that ecological effects of fishing on all animals removed by a fishery, not just bycatch or discarded catch, be measured with a variety of metrics.     

Normative barriers improvement through the MADS/MOSAR methodology

During the past 30 years, safety and environmental topics have moved up on the list of society’s significant concerns. Administrations and regulatory bodies have to publish rules for the protection of the public, decide whether to authorize the use of a chemical product or the construction of a new plant, limit the environmental impact, regulate waste disposal, etc. All these rules i.e. the legislative, normative and procedural corpus of a country, a state, a city or a factory can be designated to a barrier function. These barriers are indispensable and play an important role in industrial safety management. In developed countries, growth during the past few years in the number of laws directed at regulating environmental and safety aspects in industry is well known to everyone. Now the definition, classification and performance of the legislative and normative barriers definitely allow the management of technological risks. So it is possible to permit the identification of the flux of hazard and to perform risk reduction in order to enhance the acceptability in a regional context. A systemic risk analysis methodology was applied to Colombian industrial sectors. The current legislation was analyzed with three scenarios. A global panorama of the different existing instruments allowing future management opportunities was suggested. The obtained analysis results propose a point of view, which could be useful for a local government or a whole national system to evaluate or improve the risk legislative and normative barriers. This modeling can be applied to other countries and to other industrial sectors.     

Risk-sensitive foraging behaviour of the round-eared elephant shrew (Macroscelides proboscideus)

We examined the risk-sensitive foraging behaviour of the round-eared elephant shrew by open-economy choice experiments, in which animals were deprived of food immediately prior to experiments but given food ad libitum afterwards, to test the energy budget rule. The energy budget rule states that if an animal's (daily) energy budget is negative it should behave in a risk-prone manner. A risk-prone elephant shrew should select food from a more variable rather than a constant feeding station, although both feeding stations yield the same average return. The choice of a variable station can indicate the degree to which an animal is an energy-shortfall minimizer. Elephant shrews running below energy requirement did not choose feeding stations in accordance with the rule. Under laboratory conditions, approximating either average summer or winter temperatures, elephant shrews showed risk-averse behaviour. A polycyclic activity profile, the ability to switch the diet, and greater than expected physiological control over energy balance, may favour a continuously foraging animal such that short-term energy deficits are minimized. We argue that, under these conditions, a risk-averse response to reward-size variance is expected, because an elephant-shrew may not reliably perceive those circumstances under which risk-prone behaviour should be adopted.     

Habitat-quality effects on metapopulation dynamics in greater white-toothed shrews, Crocidura russula

The effects of patch size and isolation on metapopulation dynamics have received wide empirical support and theoretical formalization. By contrast, the effects of patch quality seem largely underinvestigated, partly due to technical difficulties in properly assessing quality. Here we combine habitat-quality modeling with four years of demographic monitoring in a metapopulation of greater white-toothed shrews (Crocidura russula) to investigate the role of patch quality on metapopulation processes. Together, local patch quality and connectivity significantly enhanced local population sizes and occupancy rates (R2 = 14% and 19%, respectively). Accounting for the quality of patches connected to the focal one and acting as potential sources improved slightly the model explanatory power for local population sizes, pointing to significant source-sink dynamics. Local habitat quality, in interaction with connectivity, also increased colonization rate (R2 = 28%), suggesting the ability of immigrants to target high-quality patches. Overall, patterns were best explained when assuming a mean dispersal distance of 800 m, a realistic value for the species under study. Our results thus provide evidence that patch quality, in interaction with connectivity, may affect major demographic processes.     

Peri-urban agro-ecosystems in the Mediterranean: diversity,dynamics, and drivers

Regional Environmental Change - To address sustainability challenges of agro-ecosystems located in Mediterranean urban regions, this paper focuses on the multidisciplinary subject of urban...