The 'dilution effect' (DE) hypothesis predicts that diverse host communities will show reduced disease. The underlying causes of pathogen dilution are complex, because they involve non-additive (driven by host interactions and differential habitat use) and additive (controlled by host species composition) mechanisms. Here, we used measures of complementarity and selection traditionally employed in the field of biodiversity-ecosystem function (BEF) to quantify the net effect of host diversity on disease dynamics of the amphibian-killing fungus Batrachochytrium dendrobatidis (Bd). Complementarity occurs when average infection load in diverse host assemblages departs from that of each component species in uniform populations. Selection measures the disproportionate impact of a particular species in diverse assemblages compared with its performance in uniform populations, and therefore has strong additive and non-additive properties. We experimentally infected tropical amphibian species of varying life histories, in single-and multi-host treatments, and measured individual Bd infection loads. Host diversity reduced Bd infection in amphibians through a mechanism analogous to complementarity (sensu BEF), potentially by reducing shared habitat use and transmission among hosts. Additionally, the selection component indicated that one particular terrestrial species showed reduced infection loads in diverse assemblages at the expense of neighbouring aquatic hosts becoming heavily infected. By partitioning components of diversity, our findings underscore the importance of additive and non-additive mechanisms underlying the DE.

Vertebrates’ gut microbial communities can be altered by the hosts’ parasites. Helminths inhabiting the gut lumen can interact directly with their host’s microbiota via physical contact, chemical products, or competition for nutrients. Indirect interactions can also occur, for instance when helminths induce or suppress host immunity in ways that have collateral effects on the microbiota. If there is genetic variation in host immune responses to parasites, we would expect such indirect effects to be conditional on host genotype. To test for such genotype by infection interactions, we experimentally exposed Gasterosteus aculeatus to their naturally co-evolved parasite, Schistocephalus solidus. The host microbiota differed in response to parasite exposure, and between infected and uninfected fish. The magnitude and direction of microbial responses to infection differed between host sexes, and also differed between variants at autosomal quantitative trait loci. These results indicate that host genotype and sex regulate the effect of helminth infection on a vertebrate gut microbiota. If this result holds in other taxa, especially humans, then helminth-based therapeutics for dysbiosis might need to be tailored to host genotype and sex.

The environmental benefits of a broad-scale adoption of biofuels are critically contingent on what current land uses will be converted for feedstock expansion and how converted land will be managed. We assessed the consequences of land use and land management for the agroindustrial production of sugarcane to the physical, chemical, and biological properties of freshwater systems. We surveyed 16 environmental variables and algae, tadpoles, predatory invertebrates, and fish in lentic water bodies distributed across a gradient in land-use intensity ranging from seasonal Atlantic Forest and cerrado to pastures to sugarcane plantations in SE Brazil, the most important sugarcane-producing region in the world. The gradient in land-use intensity was not only an axis of native habitat loss but also of ecosystem productivity, as indicated by increased conductivity, turbidity, and phytoplankton biomass. Land use had a clear signal on community and metacommunity organization, with converted land being impoverished in biodiversity relative to native habitats. However, frequency of occurrence, density, biomass, and alpha diversity of tadpoles and their predators were not affected by land use. These results suggest that sugarcane fields function as habitat to a fraction of aquatic biodiversity. Within sugarcane fields, larger wetlands surrounded by buffer strips as required by law appeared comparatively buffered against land management practices and housed a disproportional fraction of animal biomass, likely acting as sources of migrants to other water bodies in the landscape. Conversion of pastures to sugarcane fields, suggested as a strategy to reduce competition for land with food production and biodiversity conservation, does not appear to have strong consequences to lentic freshwater systems, provided that wetlands and surrounding buffer strips are preserved. These observations emphasize the importance of enforcement of legislation regulating land use (i.e. the 'Forest Code') and certification systems verifying compliance and rewarding the voluntary adoption of better land management practices.

Amphibians have been declining worldwide and the comprehension of the threats that they face could be improved by using mark–recapture models to estimate vital rates of natural populations. Recently, the consequences of marking amphibians have been under discussion and the effects of toe clipping on survival are debatable, although it is still the most common technique for individually identifying amphibians. The passive integrated transponder (PIT tag) is an alternative technique, but comparisons among marking techniques in free-ranging populations are still lacking. We compared these two marking techniques using mark–recapture models to estimate apparent survival and recapture probability of a neotropical population of the blacksmith tree frog, Hypsiboas faber. We tested the effects of marking technique and number of toe pads removed while controlling for sex. Survival was similar among groups, although slightly decreased from individuals with one toe pad removed, to individuals with two and three toe pads removed, and finally to PIT-tagged individuals. No sex differences were detected. Recapture probability slightly increased with the number of toe pads removed and was the lowest for PIT-tagged individuals. Sex was an important predictor for recapture probability, with males being nearly five times more likely to be recaptured. Potential negative effects of both techniques may include reduced locomotion and high stress levels. We recommend the use of covariates in models to better understand the effects of marking techniques on frogs. Accounting for the effect of the technique on the results should be considered, because most techniques may reduce survival. Based on our results, but also on logistical and cost issues associated with PIT tagging, we suggest the use of toe clipping with anurans like the blacksmith tree frog.

Abstract:Although São Paulo is the state with the most knowledge about anurans from Brazil, it still has important knowledge gaps about this group especially in the remnants of the Cerrado Biome. Only 0.5% of this biome is protected by conservation units in the state and remaining fragments suffer threats that include isolation, risk of fire and invasion by exotic plant species. The aim of this study was to obtain information on anurans species recorded at Estação Ecológica de Santa Bárbara, one of the few remnants in Middle Paranapanema river basin that has a predominance of open Cerrado formations. The inventory was conducted monthly from October/2008 to March/2009, totaling 30 sampling days. Surveys were conducted using pitfall traps with drift fences, incidental encounters and acoustic and visual searches. We recorded 33 anuran species, belonging to 14 genera and six families (Bufonidae, Cycloramphidae, Hylidae, Leiuperidae, Leptodactylidae e Microhylidae). Although species richness was not different between open and forest vegetation types, there was a greater abundance of anurans in the open formations, reflecting the largest association of individuals to water bodies present in open phytophysiognomies during the reproductive period. This research is an important contribution to expanding the knowledge about anurans species in the Cerrado, one of the priority global hotspots for biodiversity conservation.

AbstractThe assembly of local communities is likely to reflect the effects of local environmental factors associated with filters that act at larger spatial scales. Dissecting these multiscale effects remains a timely challenge that is particularly important for host-associated microbiomes. We investigated the relative roles of local selection (due to host species identity) and regional effects (due to water body identity) on the community structure of bacteria in the gut of tadpoles from three biogeographic areas and used graph theory and metanetwork approaches to explore and illustrate the distribution of bacteria across different ponds. The pond of origin, which represents a regional species pool of bacteria, was in general more important in shaping the gut microbiome of tadpoles than host species identity. The resulting metanetworks are modular and indicate relatively few species of bacteria occurring in more than one pond. Thus, each pond represents a relatively distinct species pool of bacteria available for community assembly of the tadpole microbiomes. Our findings indicate that microbiome community assembly in amphibian larvae, as in many other communities, is a multiscale process with important regional effects that constrain how local (i.e. host-dependent) filters act to influence microbiome community composition.

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The methodological trade‐off between the realism of natural systems and the tractability of artificial systems has led ecologists to praise the qualities of natural micro‐ and mesocosms as an ideal means for investigating the processes that organise biological communities. Among the different types of naturally occurring micro‐ and mesocosms, clusters of rock pools combine a global distribution with the simplicity, replicability, tractability and structural homogeneity that are desirable in model experimental systems. However, critical geographical data gaps in the study of rock pools must be filled if ecologists are to use these as global model systems in community ecology. In a year‐long study of a cluster of 181 rock pools in the Atlantic Forest of eastern Brazil, we conducted the first study on the ecology of freshwater rock pool communities in the entire Neotropical region, to the best of our knowledge. Building on published descriptions of the factors that drive community assembly within rock pools, we tested the hypotheses (1) that the effects of environmental factors prevail over those of spatial factors and (2) that pool volume and secondarily species interactions between consumers (anuran larvae), resources (leaf litter) and predators (dragonfly larvae) have a dominant role in driving species patterns of occurrence and abundance. Our hypotheses were generally supported as community structure was clearly influenced by the environmental characteristics of individual pools, and not to the spatial relations among them. Pool volume had a consistent, positive influence on the probability of occurrence of dragonflies and tadpoles of three anuran species, possibly through the influence of volume on hydroperiod. However, the species most strongly associated with larger pools were not those with longer times until metamorphosis, but those with larger egg clutches. In addition, species occurrences were positively associated with resource availability as measured by leaf litter mass (significantly so for Rhinella and dragonflies). These observations suggest that within these severely confined freshwater systems, indicators of environmental stability and reduced intraspecific competition could be important ultimate criteria for oviposition site selection. The ease of sampling and manipulating the rock pools at our Atlantic Forest site combined with the observation that these pools are governed by some of the same factors influencing community organisation in other rock pool systems around the world reinforces the merit of the system as a means to conduct global comparative studies of the ecology of communities and metacommunities.