Untangling the complex food webs of tropical rainforest streams.

Food webs depict the tangled web of trophic interactions associated with the functioning of an ecosystem. Understanding the mechanisms providing stability to these food webs is therefore vital for conservation efforts and the management of natural systems. Here, we first characterised a tropical stream meta-food web and five individual food webs using a Bayesian Hierarchical approach unifying three sources of information (gut content analysis, literature compilation and stable isotope data). With data on population-level biomass and individually measured body mass, we applied a bioenergetic model and assessed food web stability using a Lotka-Volterra system of equations. We then assessed the resilience of the system to individual species extinctions using simulations and investigated the network patterns associated with systems with higher stability. The model resulted in a stable meta-food web with 307 links among the 61 components. At the regional scale, 70% of the total energy flow occurred through a set of 10 taxa with large variation in body masses. The remaining 30% of total energy flow relied on 48 different taxa, supporting a significant dependency on a diverse community. The meta-food web was stable against individual species extinctions, with a higher resilience in food webs harbouring omnivorous fish species able to connect multiple food web compartments via weak, non-specialised interactions. Moreover, these fish species contributed largely to the spatial variation among individual food webs, suggesting that these species could operate as mobile predators connecting different streams and stabilising variability at the regional scale. Our results outline two key mechanisms of food web stability operating in tropical streams: (i) the diversity of species and body masses buffering against random and size-dependent disturbances and (ii) high regional diversity and weak omnivorous interactions of predators buffering against local stochastic variation in species composition. These mechanisms rely on high local and regional biodiversity in tropical streams, which is known to be strongly affected by human impacts. Therefore, an urgent challenge is to understand how the ongoing systematic loss of diversity jeopardises the stability of stream food webs in human-impacted landscapes.

As teias alimentares representam um emaranhado de interações tróficas associadas ao funcionamento de um ecossistema. Compreender os mecanismos que proporcionam estabilidade a estas teias alimentares é, portanto, vital para os esforços de conservação e gestão dos sistemas naturais. Aqui, primeiro caracterizamos uma meta teia alimentar de riachos tropicais e cinco teias alimentares individuais usando uma abordagem hierárquica Bayesiana unificando três fontes de informação (análise de conteúdo estomacal, compilação de literatura, dados de isótopos estáveis). Com dados sobre biomassa em nível populacional e massa corporal medida individualmente, aplicamos um modelo bioenergético e avaliamos a estabilidade da cadeia alimentar usando um sistema de equações Lotka­Volterra. Em seguida, avaliamos a resiliência do sistema às extinções de espécies individuais usando simulações e investigamos os padrões de rede associados a sistemas com maior estabilidade. O modelo resultou em uma meta teia alimentar estável com 307 ligações entre os 61 componentes. Na escala regional, 70% do fluxo total de energia ocorreu através de um conjunto de dez taxa com grande variação nas massas corporais. Os restantes 30% do fluxo total de energia dependiam de 47 taxa diferentes, apoiando uma dependência significativa de uma comunidade diversificada. A meta teia alimentar foi estável contra extinções de espécies individuais, com uma maior resiliência em teias alimentares que abrigam espécies de peixes onívoros capazes de conectar múltiplos compartimentos da teia alimentar através de interações fracas e não especializadas. Além disso, estas espécies de peixes contribuíram amplamente para a variação espacial entre as cadeias alimentares individuais, sugerindo que estas espécies poderiam operar como predadores móveis conectando diferentes riachos e estabilizando a variabilidade à escala regional. Nossos resultados descrevem dois mecanismos principais de estabilidade da cadeia alimentar operando em riachos tropicais: (i) a diversidade de espécies e massas corporais que protegem contra distúrbios aleatórios e dependentes do tamanho (ii) alta diversidade regional e fracas interações onívoras de predadores que protegem contra a variação estocástica local na composição de espécies. Estes mecanismos dependem de uma elevada biodiversidade local e regional em riachos tropicais, que são conhecidos por serem fortemente afetados pelos impactos humanos. Portanto, um desafio urgente é compreender como a contínua perda sistemática de diversidade põe em risco a estabilidade das teias alimentares em paisagens impactadas pelo homem.

Understanding temporal variability across trophic levels and spatial scales in freshwater ecosystems.

A tenet of ecology is that temporal variability in ecological structure and processes tends to decrease with increasing spatial scales (from locales to regions) and levels of biological organization (from populations to communities). However, patterns in temporal variability across trophic levels and the mechanisms that produce them remain poorly understood. Here we analyzed the abundance time series of spatially structured communities (i.e., metacommunities) spanning basal resources to top predators from 355 freshwater sites across three continents. Specifically, we used a hierarchical partitioning method to disentangle the propagation of temporal variability in abundance across spatial scales and trophic levels. We then used structural equation modeling to determine if the strength and direction of relationships between temporal variability, synchrony, biodiversity, and environmental and spatial settings depended on trophic level and spatial scale. We found that temporal variability in abundance decreased from producers to tertiary consumers but did so mainly at the local scale. Species population synchrony within sites increased with trophic level, whereas synchrony among communities decreased. At the local scale, temporal variability in precipitation and species diversity were associated with population variability (linear partial coefficient, ß = 0.23) and population synchrony (ß = -0.39) similarly across trophic levels, respectively. At the regional scale, community synchrony was not related to climatic or spatial predictors, but the strength of relationships between metacommunity variability and community synchrony decreased systematically from top predators (ß = 0.73) to secondary consumers (ß = 0.54), to primary consumers (ß = 0.30) to producers (ß = 0). Our results suggest that mobile predators may often stabilize metacommunities by buffering variability that originates at the base of food webs. This finding illustrates that the trophic structure of metacommunities, which integrates variation in organismal body size and its correlates, should be considered when investigating ecological stability in natural systems. More broadly, our work advances the notion that temporal stability is an emergent property of ecosystems that may be threatened in complex ways by biodiversity loss and habitat fragmentation.

Land-use intensification systematically alters the size structure of aquatic communities in the Neotropics.

Land-use and land-cover transitions can affect biodiversity and ecosystem functioning in a myriad of ways, including how energy is transferred within food-webs. Size spectra (i.e. relationships between body size and biomass or abundance) provide a means to assess how food-webs respond to environmental stressors by depicting how energy is transferred from small to larger organisms. Here, we investigated changes in the size spectrum of aquatic macroinvertebrates along a broad land-use intensification gradient (from Atlantic Forest to mechanized agriculture) in 30 Brazilian streams. We expected to find a steeper size spectrum slope and lower total biomass in more disturbed streams due to higher energetic expenditure in physiologically stressful conditions, which has a disproportionate impact on large individuals. As expected, we found that more disturbed streams had fewer small organisms than pristine forest streams, but, surprisingly, they had shallower size spectrum slopes, which indicates that energy might be transferred more efficiently in disturbed streams. Disturbed streams were also less taxonomically diverse, suggesting that the potentially higher energy transfer in these webs might be channelled via a few efficient trophic links. However, because total biomass was higher in pristine streams, these sites still supported a greater number of larger organisms and longer food chains (i.e. larger size range). Our results indicate that land-use intensification decreases ecosystem stability and enhances vulnerability to population extinctions by reducing the possible energetic pathways while enhancing efficiency between the remaining food-web linkages. Our study represents a step forward in understanding how land-use intensification affects trophic interactions and ecosystem functioning in aquatic systems.

Catchment scale deforestation increases the uniqueness of subtropical stream communities.

Local communities and individual species jointly contribute to the overall beta diversity in metacommunities. However, it is mostly unknown whether the local contribution (LCBD) and the species contribution (SCBD) to beta diversity can be predicted by local and regional environmental characteristics and by species traits and taxonomic relatedness, respectively. We investigated the LCBD and SCBD of stream benthic diatoms and insects along a gradient of land use intensification, ranging from streams in pristine forests to agricultural catchments in southeast subtropical Brazil. We expected that the LCBD would be negatively related to forest cover and positively related to the most unique streams in terms of environmental characteristics and land use (hereafter environmental and land use uniqueness, respectively). We also expected that species with a high SCBD would occur at sites with reduced forest cover. We found that the LCBD of diatoms and insects was negatively related to forest cover. The LCBD of insects was also positively related to environmental and land use uniqueness. As forest cover was negatively related to uniqueness in land use, biologically unique streams were those that deviated from the typical regional land cover. We also found that diatom traits, insect traits, and taxonomic relatedness partly explained SCBD. Furthermore, the SCBD of diatoms was positively correlated with forest cover, but the inverse was found for insects. We showed that deforestation creates novel and unique communities in subtropical streams and that species that contribute the most to beta diversity can occur at opposite ends of a land use gradient.

A Metabolic Perspective of Stochastic Community Assembly.

Metabolism controls the pace of life, driving major ecological patterns. We propose that the scaling of metabolism with temperature influences neutral processes of community assembly by controlling population dynamics independently of species identities. This perspective provides new insights into the prevalence of niche and neutral processes through universal energetic constraints.

The riverine bioreactor: An integrative perspective on biological decomposition of organic matter across riverine habitats.

Riverine ecosystems can be conceptualized as 'bioreactors' (the riverine bioreactor) which retain and decompose a wide range of organic substrates. The metabolic performance of the riverine bioreactor is linked to their community structure, the efficiency of energy transfer along food chains, and complex interactions among biotic and abiotic environmental factors. However, our understanding of the mechanistic functioning and capacity of the riverine bioreactor remains limited. We review the state of knowledge and outline major gaps in the understanding of biotic drivers of organic matter decomposition processes that occur in riverine ecosystems, across habitats, temporal dimensions, and latitudes influenced by climate change. We propose a novel, integrative analytical perspective to assess and predict decomposition processes in riverine ecosystems. We then use this model to analyse data to demonstrate that the size-spectra of a community can be used to predict decomposition rates by analysing an illustrative dataset. This modelling methodology allows comparison of the riverine bioreactor's performance across habitats and at a global scale. Our integrative analytical approach can be applied to advance understanding of the functioning and efficiency of the riverine bioreactor as hotspots of metabolic activity. Application of insights gained from such analyses could inform the development of strategies that promote the functioning of the riverine bioreactor across global ecosystems.

Community size can affect the signals of ecological drift and niche selection on biodiversity.

Ecological drift can override the effects of deterministic niche selection on small populations and drive the assembly of some ecological communities. We tested this hypothesis with a unique data set sampled identically in 200 streams in two regions (tropical Brazil and boreal Finland) that differ in macroinvertebrate community size by fivefold. Null models allowed us to estimate the magnitude to which ß-diversity deviates from the expectation under a random assembly process while taking differences in richness and relative abundance into account, i.e., ß-deviation. We found that both abundance- and incidence-based ß-diversity was negatively related to community size only in Brazil. Also, ß-diversity of small tropical communities was closer to stochastic expectations compared with ß-diversity of large communities. We suggest that ecological drift may drive variation in some small communities by changing the expected outcome of niche selection, increasing the chances of species with low abundance and narrow distribution to occur in some communities. Habitat destruction, overexploitation, pollution, and reductions in connectivity have been reducing the size of biological communities. These environmental pressures might make smaller communities more vulnerable to novel conditions and render community dynamics more unpredictable. Incorporation of community size into ecological models should provide conceptual and applied insights into a better understanding of the processes driving biodiversity.

Transcatheter mitral valve-in-valve implantation: reports of the first 50 cases from a Latin American Centre.

OBJECTIVES: Our goal was to analyse the initial results of the first 50 transapical transcatheter mitral valve-in-valve procedures performed in a single Latin American centre. METHODS: A prospective, single centre, database analysis was conducted to evaluate immediate, 30-day and 1-year postoperative results of 50 consecutive patients who had a transcatheter mitral valve-in-valve procedure from May 2015 to June 2018. All patients were operated on in a hybrid operating room and received a balloon-expandable valve via the transapical approach. Preoperative and postoperative characteristics were analysed and compared between the first 25 and the second 25 patients to evaluate the impact of the learning curve. Twenty patients had a follow-up examination at 1 year. RESULTS: There was a 98% device success rate. The patients had a mean age of 64.8 years; 72% were women; 80% were in New York Heart Association functional class ≥III preoperatively; and 36% of the procedures were urgent. The mean Society of Thoracic Surgeons scores and EuroSCORE II were 8.3% and 12.4%, respectively. Patients had a median of 2 previous operations; valve durability was 12.1 years; and 64% mitral valve disease of rheumatic fever aetiology. Echocardiography showed decreases in the maximum and mean mitral gradients from 23.5 to 14.6 and 11.5 to 6.4 mmHg postoperatively; the overall mean hospitalization period was 15 days. The overall mortality rate at 30 days was 14%, with 1 intraprocedural death. Further subanalyses between the first and the second half of the cases showed a drop in the mortality rate from 20% to 8% (P < 0.01). CONCLUSION: The transcatheter mitral valve-in-valve procedure was shown to be a safe and effective procedure to treat bioprosthetic dysfunction, with potential benefits in patients with rheumatic disease.

Ecological versatility and the assembly of multiple competitors: cautionary notes for assembly inferences.

The role of niche differences and competition is invoked when one finds coexisting species to be more dissimilar in trait composition than expected at random in community assembly studies. This approach has been questioned as competition has been hypothesized to either lead to communities assembled by similar or dissimilar species, depending on whether species similarity reflects fitness or niche differences, respectively. A current problem is that the arguments used to draw relationships between competition and species similarity are based on pairwise theoretical examples, while in nature competition can occurs among a constellation of species with different levels of versatility in resources used. By versatility we mean the documented ability of some species to escape competition for commonly used resources by changing for marginal and unused resources. Thus, a versatile species will have the ability to decrease niche overlap with all other species when facing strong competitors. When these species are embedded in multiple interactions the role of pairwise niche and fitness differences could be reduced due to indirect effects and thus competition would not be detectable. Here we developed a coexistence theory where competition occurs simultaneously among multiple species with different levels of versatility and then used it in a simulation to unravel patterns of species similarity during community assembly. We found that simulated communities can be assembled by species with more, less or equal similarity compared to a null model when using a mean distance based metric (SES.MPD). However, contrasting these varied results, we consistently found species overdispersion using a nearest neighbor-based metric (SES.MNTD), even when species differences reflected more directly their competitive abilities than their niche differences. Strong tendency to overdispersion emerged when high ecological versatility promoted large niche differences and enabled coexistence. This is because versatility to use marginal resources compensates possible fitness differences among species. Our findings provide mounting evidence of the important role of minimum niche differences and versatility in resource consumption for species embedded in multiple direct and indirect interactions.

Phylogenies and traits provide distinct insights about the historical and contemporary assembly of aquatic insect communities.

The assumption that traits and phylogenies can be used as proxies of species niche has faced criticisms. Evidence suggested that phylogenic relatedness is a weak proxy of trait similarity. Moreover, different processes can select different traits, giving opposing signals in null model analyses. To circumvent these criticisms, we separated traits of stream insects based on the concept of α and ß niches, which should give clues about assembling pressures expected to act independently of each other. We investigated the congruence between the phylogenetic structure and trait structure of communities using all available traits and all possible combinations of traits (4095 combinations). To account for hierarchical assembling processes, we analyzed patterns on two spatial scales with three pools of genera. Beta niche traits selected a priori - i.e., traits related to environmental variation (e.g., respiration type) - were consistently clustered on the smaller scale, suggesting environmental filtering, while α niche traits - i.e., traits related to resource use (e.g., trophic position) - did not display the expected overdispersion, suggesting a weak role of competition. Using all traits together provided random patterns and the analysis of all possible combinations of traits provided scenarios ranging from strong clustering to overdispersion. Communities were phylogenetically overdispersed, a pattern previously interpreted as phylogenetic limiting similarity. However, our results likely reflect the co-occurrence of ancient clades due to the stability of stream habitats along the evolutionary scale. We advise ecologists to avoid using combinations of all available traits but rather carefully traits based on the objective under consideration. Both trait and phylogenetic approaches should be kept in the ecologist toolbox, but phylogenetic distances should not be used as proxies of traits differences. Although the phylogenetic structure revealed processes operating at the evolutionary scale, only specific traits explained local processes operating in our communities.

Phylogenetic clustering among aggressive competitors: evidence from odonate assemblages along a riverine gradient.

Studies on phylogenetic community ecology usually infer habitat filtering when communities are phylogenetically clustered or competitive exclusion when communities are overdispersed. This logic is based on strong competition and niche similarity among closely related species-a less common phenomenon than previously expected. Dragonflies and damselflies are good models for testing predictions based on this logic because they behave aggressively towards related species due to mistaken identification of conspecifics. This behavior may drive communities toward phylogenetic overdispersion if closely related species frequently exclude each other. However, phylogenetically clustered communities could also be observed if habitat filtering and/or competitive asymmetry among distantly related species are major drivers of community assembling. We investigated the phylogenetic structure of odonate assemblages in central Brazil in a watershed characterized by variations in stream width, vegetation cover, aquatic vegetation, and luminosity. We observed general clustering in communities according to two indices of phylogenetic structure. Phylogenetic beta diversity coupled with Mantel tests and RLQ analysis evidenced a correlation between the riverine gradient and phylogenetic structure. Larger rivers with aquatic vegetation were characterized by anisopterans, while most zygopterans stayed in small and shaded streams. These results indicate niche conservatism in Odonata habitat occupancy, and that the environment is a major influence on the phylogenetic structure of these communities. We suggest that this is due to clade-specific ecophysiological requirements, and because closely related species may also have competitive advantages and dominate certain preferred habitats.

Characterization of galls, insect galls and associated fauna of Ecological Station of Jataí (Luiz Antônio, SP) / Caracterização de galhas, insetos galhadores e fauna associada de Estação Ecológica de Jataí (Luiz Antônio, SP)

This is the first study about galls, gall makers and associated fauna of the Ecological Station of Jataí. Galls are plant structures formed by abnormal growth of cells, tissues or organs induced by several organisms, as fungous, nematoids and insects. Five areas of the conservation unity, two in the phytophysionomy of cerrado in regeneration and three in the cerradão area were studied, totalizing 69 morphotypes of galls on 41 host species from 24 families. This is the first record of Annonaceae as the richest family in morphotypes in Brazil; 34 gall makers and associated fauna were identified, which 23 Diptera (67.4%), eight Hymenoptera (23.5%), two Hemiptera (5.8%) and one Thysanoptera (2.9%). Were described 41 new morphotypes of gall and made the first characterization of gall on Maprounea guianensis Aubl., Acosmium subelegans (Mohlenbr.) Yakovlev., Strychnosbicolor Progel, Eriotheca gracilipes K. Schum., Stryphnodendron obovatum Benth., Broyesum gaudichaudii Trécul, Psychotria suterella Müll. Arg., Psychotria trichophora Müll. Arg. and Serjania erecta Radlk.

Este é o primeiro estudo sobre galhas, insetos galhadores e fauna associada da Estação Ecológica de Jataí. Galhas são estruturas vegetais formadas por um crescimento anormal de células, tecidos ou órgãos induzido por vários organismos, como fungos, nematóides e insetos. Cinco áreas da unidade de conservação, dois na fitofisionomia de cerrado em regeneração e três na área de cerradão foram estudadas, totalizando 69 morfotipos de galhas em 41 espécies de plantas hospedeiras de 24 famílias. Este é o primeiro registro de Annonaceae como a família mais rica em morfotipos no Brasil; 34 insetos galhadores e fauna associada foram identificados, sendo 23 Diptera (67,4%), oito Hymenoptera (23,5%), dois Hemiptera (5,8%) e um Thysanoptera (2,9%). Foram descritos 41 novos morfotipos de galhas e foi feita a primeira caracterização de galhas em Xylopia aromatica (Lam.) Mart., Connarus suberosus Planch., Maprounea guianensis Aubl., Acosmium subelegans (Mohlenbr.) Yakovlev., Strychnos bicolor Progel, Eriotheca gracilipes K. Schum., Stryphnodendron obovatum Benth., Broyesum gaudichaudii Trécul, Psychotria suterella Müll. Arg., Psychotria trichophora Müll. Arg. e Serjania erecta Radlk.