Partitioning the factors of spatial variation in regeneration density of shade-tolerant tree species

Understanding coexistence of highly shade-tolerant tree species is a longstanding challenge for forest ecologists. A conceptual model for the coexistence of sugar maple (Acer saccharum) and American beech (Fagus grandibfolia) has been proposed, based on a low-light survival/high-light growth trade-off, which interacts with soil fertility and small-scale spatiotemporal variation in the environment. In this study, we first tested whether the spatial distribution of seedlings and saplings can be predicted by the spatiotemporal variability of light availability and soil fertility, and second, the manner in which the process of environmental filtering changes with regeneration size. We evaluate the support for this hypothesis relative to the one for a neutral model, i.e., for seed rain density predicted from the distribution of adult trees. To do so, we performed intensive sampling over 86 quadrats (5 x 5 m) in a 0.24-ha plot in a mature maple-beech community in Quebec, Canada. Maple and beech abundance, soil characteristics, light availability, and growth history (used as a proxy for spatiotemporal variation in light availability) were finely measured to model variation in sapling composition across different size classes. Results indicate that the variables selected to model species distribution do effectively change with size, but not as predicted by the conceptual model. Our results show that variability in the environment is not sufficient to differentiate these species' distributions in space. Although species differ in their spatial distribution in the small size classes, they tend to correlate at the larger size class in which recruitment occurs. Overall, the results are not supportive of a model of coexistence based on small-scale variations in the environment. We propose that, at the scale of a local stand, the lack of fit of the model could result from the high similarity of species in the range of environmental conditions encountered, and we suggest that coexistence would be stable only at larger spatial scales at which variability in the environment is greater.     

A dusk chorus effect in a nocturnal bird: support for mate and rival assessment functions

The dawn chorus is a striking feature of spring mornings and a characteristic behaviour of many bird species, particularly the passerines. Dawn singing has been considered a reliable signal of male quality for mate and rival assessment. Singing is presumed to be relatively costly at dawn both because air temperatures are relatively low and because birds have not fed overnight. Models of optimal daily routine predict the existence of a “dusk chorus” in nocturnal birds, although this prediction has received little empirical attention. Nocturnal birds at dusk may be energy-limited because of a lack of daytime feeding, and singing at dusk may thus ensure signal reliability. Here, we used an observational and experimental approach to study vocal behaviour at dusk and dawn in a nocturnal raptor, the little owl Athene noctua. We assess whether male little owls adjust their vocal behaviour according to feeding stage (i.e. period of the night), ambient air temperature and territorial context (i.e. spontaneous calling behaviour vs elicited calling by intrusion). Across different temperatures, we find that both spontaneous vocal activity and inter-individual variability in call duration increased at dusk, clearly indicating a dusk chorus phenomenon. Results from playback presentations suggest that food, rather than air temperature, is likely to be more constraining at dusk. We discuss how comparing dusk and dawn choruses in nocturnal and diurnal species can provide insights into both mechanistic and functional aspects of signalling behaviour.     

Release of particles and metals into seawater following sediment resuspension of a coastal mine tailings disposal off Portmán Bay,Southern Spain

Environmental Science and Pollution Research - Portmán Bay in Southern Spain is one of the most extreme cases in Europe of anthropogenic impact on the marine ecosystem by the disposal of mine...     

Rate of pesticide volatilization from soil: an experimental approach with a wind tunnel system applied to trifluralin

Pesticide volatilization to the atmosphere may be a major pathway of dissipation closely linked with environmental, physico-chemical and technical factors. Understanding the volatilization process requires systems that make it possible to control some of these factors. Wind tunnels meet to these criteria. The volatilization flux is determined from a mass balance, using the difference in atmospheric pesticide concentration between the entrance and the exit of the tunnel and the airflow rate. An experiment was carried out in June 2000 to study the repeatability of this technique. Volatilization of trifluralin was measured in three wind tunnels for 8 days with a sampling period varying between 3 h and 2 days. Pesticide concentration was determined by trapping by XAD-2 resin in a two-stage cartridge, solvent extraction and analysis by gas chromatography. Cumulated losses through volatilization reached 30% of the measured application dose after 8 days, with a variability of less than 20% between the three tunnels. Approximately 20% remained in the topsoil (0–2 cm), with a variability of 14% between the three tunnels. The decrease in the volatilization flux over time is coherent with the expected theoretical evolution for a volatile pesticide such as trifluralin and with previous experimental works.     

Environmental fate of chlordecone in coastal habitats: recent studies conducted in Guadeloupe and Martinique (Lesser Antilles)

Environmental Science and Pollution Research - The organochlorine pollution by chlordecone, an insecticide spread in the past in banana plantations, is now recognized as a major ecological,...     

Comparison of percolation to batch and sequential leaching tests: Theory and data

This article constitutes a brief discussion of the article by Grathwohl and Susset (2009) on the interpretation of column and batch leaching tests. The objective of the discussion is to contribute to certain issues raised by the original article, with particular reference to data presented by Guyonnet et al. (2008) in this journal and cited by the authors.     

Organochlorine pollution in tropical rivers (Guadeloupe): role of ecological factors in food web bioaccumulation

Concentrations of organochlorine pesticides and stable isotope ratios of nitrogen and carbon were measured in a tropical freshwater ecosystem to evaluate the contamination level of biota and examine the bioaccumulation patterns of pollutants through the food web. Chemical analyses showed a general and heavy contamination of the entire food web. They revealed the strong accumulation of pollutants by juveniles of diadromous fishes and shrimps, as they re-enter the river. The role of ecological factors in the bioaccumulation of pesticides was evaluated. Whereas the most persistent pollutants (chlordecone and monohydro-chlordecone) were related to the organisms diet and habitat, bioaccumulation of β-HCH was only influenced by animal lipid content. The biomagnification potential of chlordecone through the food chain has been demonstrated. It highlighted the importance of trophic transfer in this compound bioaccumulation process. In contrast, bioconcentration by passive diffusion from water seemed to be the main exposure route of biota to β-HCH.     

Effect of canopy removal on a rocky shore community metabolism and structure

The effects of the permanent removal of the canopy-forming alga Fucus serratus was studied in terms of both functioning and diversity on a mid–low rocky shore ecosystem in the south-west English Channel (48°N 43.686′, 3°W 59.282′). Ecosystem functioning was examined as net or gross primary productivity (NPP or GPP) and respiration (Resp) measured through CO₂ fluxes. Diversity was examined as number and composition of species. Measurements were performed in situ, during emersion times, without altering target assemblages. The experiment was designed with two treatments [control (C) or canopy removed (CR)] and five replicates, and was conducted over an 18-month period (from February 2006 to August 2007) to integrate the seasonal variability. The mean GPP and Resp were severely reduced in CR treatment compared to control throughout the survey. The mean NPP was not affected at first, due to the development of opportunistic green algae, but was drastically reduced after 9 months of experiment. The canopy removal affected neither the number of species nor their distribution among trophic groups, and the algal community was only slightly affected. The abundance and biomass of mobile invertebrates, however, were greatly reduced in the absence of canopy. This indicates an important effect of the dominant alga on the higher trophic levels of the community. At this tidal level, the canopy did not seem to affect the community by dampening the environmental stress but by providing food, habitat or both.     

From bioavailability to risk assessment of polluted soil using snails: link between excess transfer and inhibition of sexual maturation

Environmental Science and Pollution Research - An accurate assessment of the environmental risk of soils contaminated by metal(loid)s (MEs) requires quantifying exposure and knowing the toxicity of...