Arsenic bioaccessibility in a gold mining area: a health risk assessment for children

High concentrations of total arsenic (As) have been measured in soils of gold mining areas of Brazil. However, bioaccessibility tests have not yet been conducted on those materials, which is essential for better health risk estimates. This study aimed at?evaluating As bioaccessibility in samples from a gold mining area located in Brazil and assessing children's exposure to As-contaminated materials. Samples were collected from different materials (a control and four As-contaminated soils/sediments) found in a gold mine area located in Paracatu (MG), Brazil. Total and bioaccessible As concentrations were determined for all samples. The control soil presented the lowest As concentrations, while all other materials contained high total As concentrations (up to 2,666?mg?kg(-1)) and low bioaccessible As percentage (<4.2%), indicating a low risk from exposure of resident children next to this area. The calculated dose of exposure indicated that, except for the pond tailings, in all other areas, the exposure route considering soil ingestion contributed at most to 9.7% of the maximum As allowed ingestion per day (0.3?μg?kg(-1) BW day(-1)).     

A universal approach to estimate biomass and carbon stock in tropical forests using generic allometric models

Allometric equations allow aboveground tree biomass and carbon stock to be estimated from tree size. The allometric scaling theory suggests the existence of a universal power-law relationship between tree biomass and tree diameter with a fixed scaling exponent close to 8/3. In addition, generic empirical models, like Chave's or Brown's models, have been proposed for tropical forests in America and Asia. These generic models have been used to estimate forest biomass and carbon worldwide. However, tree allometry depends on environmental and genetic factors that vary from region to region. Consequently, theoretical models that include too few ecological explicative variables or empirical generic models that have been calibrated at particular sites are unlikely to yield accurate tree biomass estimates at other sites. In this study, we based our analysis on a destructive sample of 481 trees in Madagascar spiny dry and moist forests characterized by a high rate of endemism (> 95%). We show that, among the available generic allometric models, Chave's model including diameter, height, and wood specific gravity as explicative variables for a particular forest type (dry, moist, or wet tropical forest) was the only one that gave accurate tree biomass estimates for Madagascar (R2 > 83%, bias < 6%), with estimates comparable to those obtained with regional allometric models. When biomass allometric models are not available for a given forest site, this result shows that a simple height-diameter allometry is needed to accurately estimate biomass and carbon stock from plot inventories.     

Landscape context and scale differentially impact coffee leaf rust, coffee berry borer, and coffee root-knot nematodes

Crop pest and disease incidences at plot scale vary as a result of landscape effects. Two main effects can be distinguished. First, landscape context provides habitats of variable quality for pests, pathogens, and beneficial and vector organisms. Second, the movements of these organisms are dependent on the connectivity status of the landscape. Most of the studies focus on indirect effects of landscape context on pest abundance through their predators and parasitoids, and only a few on direct effects on pests and pathogens. Here we studied three coffee pests and pathogens, with limited or no pressure from host-specific natural enemies, and with widely varying life histories, to test their relationships with landscape context: a fungus, Hemileia vastatrix, causal agent of coffee leaf rust; an insect, the coffee berry borer, Hypothenemus hampei (Coleoptera: Curculionidae); and root-knot nematodes, Meloidogyne spp. Their incidence was assessed in 29 coffee plots from Turrialba, Costa Rica. In addition, we characterized the landscape context around these coffee plots in 12 nested circular sectors ranging from 50 to 1500 m in radius. We then performed correlation analysis between proportions of different land uses at different scales and coffee pest and disease incidences. We obtained significant positive correlations, peaking at the 150 m radius, between coffee berry borer abundance and proportion of coffee in the landscape. We also found significant positive correlations between coffee leaf rust incidence and proportion of pasture, peaking at the 200 m radius. Even after accounting for plot level predictors of coffee leaf rust and coffee berry borer through covariance analysis, the significance of landscape structure was maintained. We hypothesized that connected coffee plots favored coffee berry borer movements and improved its survival. We also hypothesized that wind turbulence, produced by low-wind-resistance land uses such as pasture, favored removal of coffee leaf rust spore clusters from host surfaces, resulting in increased epidemics. In contrast, root-knot nematode population density was not correlated to landscape context, possibly because nematodes are almost immobile in the soil. We propose fragmenting coffee plots with forest corridors to control coffee berry borer movements between coffee plots without favoring coffee leaf rust dispersal.     

Catastrophe and the life span of coral reefs

A strong earthquake in the western Caribbean in 2009 had a catastrophic impact on uncemented, unconsolidated coral reefs in the central sector of the shelf lagoon of the Belizean barrier reef. In a set of 21 reef sites that had been observed prior to the earthquake, the benthic assemblages of 10 were eradicated, and one was partially damaged, by avalanching of their slopes. Ecological dynamics that had played out over the previous 23 years, including the mass mortalities of two sequentially dominant coral species and a large increase in the cover of an encrusting sponge, were instantaneously rendered moot in the areas of catastrophic reef-slope failure. Because these prior dynamics also determined the benthic composition and resilience of adjacent sections of reef that remained intact, the history of disturbance prior to the earthquake will strongly influence decadal-scale recovery in the failed areas. Geological analysis of the reef framework yielded a minimum return time of 2000-4000 years for this type of high-amplitude event. Anthropogenic degradation of ecosystems must be viewed against the backdrop of long-period, natural catastrophes, such as the impact of strong earthquakes on uncemented, lagoonal reefs.     

Trait similarity patterns within grass and grasshopper communities: multitrophic community assembly at work

Trait-based community assembly theory suggests that trait variation among co-occurring species is shaped by two main processes: abiotic filtering, important in stressful environments and promoting similarity, and competition, more important in productive environments and promoting dissimilarity. Previous studies have indeed found trait similarity to decline along productivity gradients. However, these studies have always been done on single trophic levels. Here, we investigated how interactions between trophic levels affect trait similarity patterns along environmental gradients. We propose three hypotheses for the main drivers of trait similarity patterns of plants and herbivores along environmental gradients: (1) environmental control of both, (2) bottom-up control of herbivore trait variation, and (3) top-down control of grass trait variation. To test this, we collected data on the community composition and trait variation of grasses (41 species) and grasshoppers (53 species) in 50 plots in a South African savanna. Structural equation models were used to investigate how the range and spacing of within-community functional trait values of both grasses and their insect herbivores (grasshoppers; Acrididae) respond to (1) rainfall and fire frequency gradients and (2) the trait similarity patterns of the other trophic level. The analyses revealed that traits of co-occurring grasses became more similar toward lower rainfall and higher fire frequency (environmental control), while showing little evidence for top-down control. Grasshopper trait range patterns, on the other hand, were mostly directly driven by vegetation structure and grass trait range patterns (bottom-up control), while environmental factors had mostly indirect effects via plant traits. Our study shows the potential to expand trait-based community assembly theory to include trophic interactions.     

Ecological determinism increases with organism size

After much debate, there is an emerging consensus that the composition of many ecological communities is determined both by species traits, as proposed by niche theory, as well as by chance events. A critical question for ecology is, therefore, which attributes of species predict the dominance of deterministic or stochastic processes. We outline two hypotheses by which organism size could determine which processes structure ecological communities, and we test these hypotheses by comparing the community structure in bromeliad phytotelmata of three groups of organisms (bacteria, zooplankton, and macroinvertebrates) that encompass a 10 000-fold gradient in body size, but live in the same habitat. Bacteria had no habitat associations, as would be expected from trait-neutral stochastic processes, but still showed exclusion among species pairs, as would be expected from niche-based processes. Macroinvertebrates had strong habitat and species associations, indicating niche-based processes. Zooplankton, with body size between bacteria and macroinvertebrates, showed intermediate habitat associations. We concluded that a key niche process, habitat filtering, strengthened with organism size, possibly because larger organisms are both less plastic in their fundamental niches and more able to be selective in dispersal. These results suggest that the relative importance of deterministic and stochastic processes may be predictable from organism size.     

Energy budgets reveal equal benefits of varied migration strategies in northern gannets

We investigated migration and wintering of adult northern gannets (Morus bassanus) breeding in east Scotland, North Sea, by deploying geolocation loggers over three winters. The wintering ranges of these birds varied from the North Sea to the Atlantic off West Africa. Flight time was taken as a proxy for migration and foraging effort. Gannets wintering off Africa had higher total flight times during migration than birds wintering further north. Total flight times in different wintering regions were generally low. Birds off West Africa consistently spent < 25 % of daylight hours in flight, but birds further north showed more variable values that may reflect more variable weather or food availability. Winter sea surface temperatures ranged from 9 °C (North Sea) to 16 °C (West Africa). Thermostatic costs in winter as estimated by measuring thermal conductance in carcasses in still air and water were 28 % higher in North Sea than off West Africa. This effect is aggravated by higher thermostatic costs caused by stronger wind chills in the North Sea compared to the conditions off West Africa. Birds wintering close to the UK arrived at the colony on average 12 days earlier than birds wintering off West Africa. We conclude that the net cost-benefit analysis may be similar for all wintering areas investigated.     

Food sources used by sediment meiofauna in an intertidal Zostera noltii seagrass bed: a seasonal stable isotope study

In an intertidal Zostera noltii Hornem seagrass bed, food sources used by sediment meiofauna were determined seasonally by comparing stable isotope signatures (δ¹³C, δ¹⁵N) of sources with those of nematodes and copepods. Proportions of different carbon sources used by consumers were estimated using the SIAR mixing model on δ¹³C values. Contrary to δ¹⁵N values, food source mean δ¹³C values encompassed a large range, from −22.1 ‰ (suspended particulate organic matter) to −10.0 ‰ (Z. noltii roots). δ¹³C values of copepods (from −22.3 to −12.3 ‰) showed that they use many food sources (benthic and phytoplanktonic microalgae, Z. noltii matter). Nematode δ¹³C values ranged from −14.6 to −11.4 ‰, indicating a strong role of microphytobenthos and/or Z. noltii matter as carbon sources. The difference of food source uses between copepods and nematodes is discussed in light of source accessibility and availability.     

Molecular prey identification in wild Octopus vulgaris paralarvae

The trophic ecology of Octopus vulgaris paralarvae collected in 2008 off the Ría de Vigo, NW Spain (42° 12.80′ N–9° 00.00′ W), was approached by both morphological and molecular methods. External digestion of prey and posterior suction of the liquefied contents by wild O. vulgaris paralarvae made the morphological identification of gut contents impossible. Thus, a PCR-based method using group-specific primers was selected to identify prey consumed by O. vulgaris paralarvae in the pelagic realm. The mitochondrial ribosomal 16S gene region was chosen for designing group-specific primers, which targeted a broad range of crustaceans and fishes but avoided the amplification of predator DNA. These primers successfully amplified DNA of prey by using a semi-nested PCR-based approach and posterior cloning. Homology search and phylogenetic analysis were then conducted with the 20 different operational taxonomic units obtained to identify the putative organisms ingested. The phylogenetic analysis clustered ingested prey into 12 families of crustaceans (11 belonging to the order Decapoda and 1 to the order Euphausiacea) and two families of fishes (Gobiidae and Carangidae). According to the Czekanowski’s Index (CI), the trophic niche breadth of O. vulgaris paralarvae is low (CI = 0.13), which means that these paralarvae are specialist predators at least during the first weeks of their life cycle. It is the first time that natural prey has been identified in O. vulgaris paralarvae collected from the wild, and such knowledge may be critical to increasing the survival of O. vulgaris hatchlings in captivity, a goal that has been actively pursued since the 1960s by aquaculture researchers.