601 research outputs found

    Richard Carl Vogt (1949–2021)

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    Um modelo de crescimento de Paleosuchus trigonatus (Crocodylia: Alligatoridae) do Rio Negro prevê o crescimento de indivíduos do rio Xingu, Brasil

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    Patterns of growth of crocodilians vary geographically within the same species, so models developed in one area may not predict size-age relationships in others. We used recapture data for three females and six males of Paleosuchus trigonatus from the Belo Monte hydroelectric dam area on the Xingu River to validate a growth model developed on a tributary of the Rio Negro. Individuals were recaptured between two and 10 years after marking (2012–2022). The data indicate that the monomolecular (von Bertalanffy by length) model is adequate to model growth of intermediate size animals. Recapture of one female after eight years indicates that the Rio Negro model can be used to model growth with accuracy for individuals from the Xingu River.Os padrões de crescimento dos crocodilianos variam geograficamente dentro da mesma espécie, de modo que os modelos desenvolvidos em uma área não preveem relações tamanho-idade em outras. Usamos dados de recaptura de três fêmeas e seis machos de Paleosuchus trigonatus da área da hidrelétrica de Belo Monte no rio Xingu para validar um modelo de crescimento desenvolvido em um afluente do rio Negro. Os jacarés foram recapturados entre dois e dez anos após a marcação (2012–2022). Os dados indicam que o modelo monomolecular (von Bertalanffy por comprimento) é adequado para modelar o crescimento de animais de tamanho intermediário, e a recaptura de uma fêmea após oito anos indica que o modelo Rio Negro pode ser usado para modelar o crescimento com razoável precisão para indivíduos do Rio Xingu

    Different environmental gradients affect different measures of snake β-diversity in the Amazon rainforests

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    Mechanisms generating and maintaining biodiversity at regional scales may be evaluated by quantifying β-diversity along environmental gradients. Differences in assemblages result in biotic complementarities and redundancies among sites, which may be quantified through multi-dimensional approaches incorporating taxonomic β-diversity (TBD), functional β-diversity (FBD) and phylogenetic β-diversity (PBD). Here we test the hypothesis that snake TBD, FBD and PBD are influenced by environmental gradients, independently of geographic distance. The gradients tested are expected to affect snake assemblages indirectly, such as clay content in the soil determining primary production and height above the nearest drainage determining prey availability, or directly, such as percentage of tree cover determining availability of resting and nesting sites, and climate (temperature and precipitation) causing physiological filtering. We sampled snakes in 21 sampling plots, each covering five km2, distributed over 880 km in the central-southern Amazon Basin. We used dissimilarities between sampling sites to quantify TBD, FBD and PBD, which were response variables in multiple-linear-regression and redundancy analysis models. We show that patterns of snake community composition based on TBD, FBD and PBD are associated with environmental heterogeneity in the Amazon. Despite positive correlations between all β-diversity measures, TBD responded to different environmental gradients compared to FBD and PBD. Our findings suggest that multi-dimensional approaches are more informative for ecological studies and conservation actions compared to a single diversity measure

    Body size predicts ontogenetic nitrogen stable-isotope (δ15N) variation, but has little relationship with trophic level in ectotherm vertebrate predators

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    Large predators have disproportionate efects on their underlying food webs. Thus, appropriately assigning trophic positions has important conservation implications both for the predators themselves and for their prey. Large-bodied predators are often referred to as apex predators, implying that they are many trophic levels above primary producers. However, theoretical considerations predict both higher and lower trophic position with increasing body size. Nitrogen stable isotope values (δ15N) are increasingly replacing stomach contents or behavioral observations to assess trophic position and it is often assumed that ontogenetic dietary shifts result in higher trophic positions. Intraspecifc studies based on δ15N values found a positive relationship between size and inferred trophic position. Here, we use datasets of predatory vertebrate ectotherms (crocodilians, turtles, lizards and fshes) to show that, although there are positive intraspecifc relationships between size and δ15N values, relationships between stomach-content-based trophic level (TPdiet) and size are undetectable or negative. As there is usually no single value for 15N trophic discrimination factor (TDF) applicable to a predator species or its prey, estimates of trophic position based on δ15N in ectotherm vertebrates with large size ranges, may be inaccurate and biased. We urge a reconsideration of the sole use of δ15N values to assess trophic position and encourage the combined use of isotopes and stomach contents to assess diet and trophic level.Fil: Villamarín, Francisco. Universidad Regional Amazónica Ikiam; EcuadorFil: Jardine, Timothy D.. University of Saskatchewan; CanadáFil: Bunn, Stuart E.. Griffith University; AustraliaFil: Malvásio, Adriana. Universidade Federal Do Tocantins (ufdt);Fil: Piña, Carlos Ignacio. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; ArgentinaFil: Jacobi, Cristina Mariana. Universidade de Sao Paulo; BrasilFil: Araújo, Diogo Dutra. Universidad de Vale do Rio dos Sinos; BrasilFil: de Brito, Elizângela Silva. Universidade Federal Do Mato Grosso (ufmt);Fil: de Moraes Carvalho, Felipe. Virginia Polytechnic Institute; Estados UnidosFil: da Costa, Igor David. Universidade Federal Fluminense; BrasilFil: Verdade, Luciano Martins. Wildlife Management Consultancy; BrasilFil: Lara, Neliton. Universidade de Sao Paulo; BrasilFil: de Camargo, Plínio Barbosa. Universidade de Sao Paulo; BrasilFil: Miorando, Priscila Saikoski. Universidade Federal do Pará; BrasilFil: Costa Gonçalves Portelinha, Thiago. Universidade Federal de Tocantins; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Marques, Thiago Simon. Universidade de Sorocaba; BrasilFil: Magnusson, William E.. Instituto Nacional de Pesquisas da Amazônia; Brasi

    Experiment, monitoring, and gradient methods used to infer climate change effects on plant communities yield consistent patterns

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    Inference about future climate change impacts typically relies on one of three approaches: manipulative experiments, historical comparisons (broadly defined to include monitoring the response to ambient climate fluctuations using repeat sampling of plots, dendroecology, and paleoecology techniques), and space-for-time substitutions derived from sampling along environmental gradients. Potential limitations of all three approaches are recognized. Here we address the congruence among these three main approaches by comparing the degree to which tundra plant community composition changes (i) in response to in situ experimental warming, (ii) with interannual variability in summer temperature within sites, and (iii) over spatial gradients in summer temperature. We analyzed changes in plant community composition from repeat sampling (85 plant communities in 28 regions) and experimental warming studies (28 experiments in 14 regions) throughout arctic and alpine North America and Europe. Increases in the relative abundance of species with a warmer thermal niche were observed in response to warmer summer temperatures using all three methods; however, effect sizes were greater over broad-scale spatial gradients relative to either temporal variability in summer temperature within a site or summer temperature increases induced by experimental warming. The effect sizes for change over time within a site and with experimental warming were nearly identical. These results support the view that inferences based on space-for-time substitution overestimate the magnitude of responses to contemporary climate warming, because spatial gradients reflect long-term processes. In contrast, in situ experimental warming and monitoring approaches yield consistent estimates of the magnitude of response of plant communities to climate warming
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