Body size–trophic position relationships among fishes of the lower Mekong basin

Body size is frequently claimed to be a major determinant of animal trophic interactions, yet few studies have explored relationships between body size and trophic interactions in rivers, especially within the tropics. We examined relationships between body size and trophic position (TP) within fish assemblages in four lowland rivers of the Lower Mekong Basin in Cambodia. Stable isotope analysis (based on δ(15)N) was used to estimate TP of common fish species in each river, and species were classified according to occupation of benthic versus pelagic habitats and major feeding guilds. Regression analysis yielded strong correlations between body size and TP among fishes from the Sesan and Sreprok rivers, but not those from the Mekong and Sekong rivers. The Mekong fish assemblage had higher average TP compared with those of other rivers. The relationship between body size and TP was positive and significantly correlated for piscivores and omnivores, but not for detritivores and insectivores. The body size–TP relationship did not differ between pelagic and benthic fishes. Body size significantly predicted TP within the orders Siluriformes and Perciformes, but not for Cypriniformes, the most species-rich and ecologically diverse order in the Lower Mekong River. We conclude that for species-rich, tropical fish assemblages with many detritivores and invertivores, body size would not be an appropriate surrogate for TP in food web models and other ecological applications

Diet-Morphology Correlations in the Radiation of South American Geophagine Cichlids (Perciformes: Cichlidae: Cichlinae)

Genera within the South American cichlid tribe Geophagini display specialized feeding and reproductive strategies, with some taxa specialized for both substrate-sifting and mouth brooding. Several lineages within the clade also possess an epibranchial lobe (EBL), a unique pharyngeal structure that has been proposed to have a function in feeding and/or mouth brooding. A recently published genus-level phylogeny of Neotropical cichlids was used as the evolutionary framework for investigating the evolution of morphological features presumably correlated with diet and mouth brooding in the tribe Geophagini. We tested for possible associations between the geophagine epibranchial lobe and benthic feeding and mouth brooding. We also addressed whether the EBL may be associated with unique patterns of diversification in certain geophagine clades. Tests of binary character correlations revealed the EBL was significantly associated with mouth brooding. We also tested for a relationship between diet and morphology. We analyzed stomach contents and morphometric variation among 21 species, with data for two additional species obtained from the literature. Principal Components Analysis revealed axes of morphological variation significantly correlated with piscivory and benthivory, and both morphology and diet were significantly associated with phylogeny. These results suggest that the EBL could be an adaptation for either feeding or mouth brooding. The EBL, however, was not associated with species richness or accelerated rates of phyletic diversification

How do lizard niches conserve, diverge or converge? Further exploration of saurian evolutionary ecology

Background: Environmental conditions on Earth are repeated in non-random patterns that often coincide with species from different regions and time periods having consistent combinations of morphological, physiological and behavioral traits. Observation of repeated trait combinations among species confronting similar environmental conditions suggest that adaptive trait combinations are constrained by functional tradeoffs within or across niche dimensions. In an earlier study, we assembled a high-resolution database of functional traits for 134 lizard species to explore ecological diversification in relation to five fundamental niche dimensions. Here we expand and further examine multivariate relationships in that dataset to assess the relative influence of niche dimensions on the distribution of species in 6-dimensional niche space and how these may deviate from distributions generated from null models. We then analyzed a dataset with lower functional-trait resolution for 1023 lizard species that was compiled from our dataset and a published database, representing most of the extant families and environmental conditions occupied by lizards globally. Ordinations from multivariate analysis were compared with null models to assess how ecological and historical factors have resulted in the conservation, divergence or convergence of lizard niches. Results: Lizard species clustered within a functional niche volume influenced mostly by functional traits associated with diet, activity, and habitat/substrate. Consistent patterns of trait combinations within and among niche dimensions yielded 24 functional groups that occupied a total niche space significantly smaller than plausible spaces projected by null models. Null model tests indicated that several functional groups are strongly constrained by phylogeny, such as nocturnality in the Gekkota and the secondarily acquired sit-and-wait foraging strategy in Iguania. Most of the widely distributed and species-rich families contained multiple functional groups thereby contributing to high incidence of niche convergence. Conclusions: Comparison of empirical patterns with those generated by null models suggests that ecological filters promote limited sets of trait combinations, especially where similar conditions occur, reflecting both niche convergence and conservatism. Widespread patterns of niche convergence following ancestral niche diversification support the idea that lizard niches are defined by trait-function relationships and interactions with environment that are, to some degree, predictable and independent of phylogeny.Fil: Pelegrin, Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; ArgentinaFil: Winemiller, Kirk Owen. Texas A&M University; Estados UnidosFil: Vitt, Laurie J.. University Of Oklahoma; Estados UnidosFil: Fitzgerald, Daniel B.. United States Geological Survey; Estados UnidosFil: Pianka, Eric R. University of Texas at Austin; Estados Unido

Hydrogen sulfide, bacteria, and fish: a unique, subterranean food chain

Photoautotrophs are generally considered to be the base of food webs, and habitats that lack light, such as caves, frequently rely on surface-derived carbon. Here we show, based on analysis of gut contents and stable isotope ratios of tissues (13C:12C and 15N:14N), that sulfur-oxidizing bacteria are directly consumed and assimilated by the fish Poecilia mexicana in a sulfide-rich cave stream in Tabasco state, Mexico. Our results provide evidence of a vertebrate deriving most of its organic carbon and nitrogen from in situ chemoautotrophic production, and reveals the importance of alternative energy production sources supporting animals in extreme environments.Peer reviewedZoolog

Do wood-grazing fishes partition their niche?: morphological and isotopic evidence for trophic segregation in Neotropical Loricariidae

Summary 1. Morphic detritus, including coarse particulate organic matter such as terrestrial tree leaves and wood, is consumed by few fishes in temperate stream systems but is ingested by abundant and diverse groups of specialized fishes in tropical rivers; physiological assimilation and partitioning of morphic detritus by fishes remain poorly understood. 2. This study examines seven species of Neotropical suckermouth-armored catfishes (Loricariidae) that live among and feed on coarse woody debris. Five species represent two unrelated evolutionary lineages showing convergent morphological specializations for gouging into and eating wood, small particles of which fill their guts. Two morphologically distinct species unrelated to wood-eaters and to each other forage along the surface of wood. 3. We examined six jaw functional morphological characteristics of each loricariid species as well as C and N stable isotope ratios of blood plasma, red blood cells and fin tissue of three wood-eating species and muscle tissues of all seven species. Consumer isotopic signatures were compared among species and with isotopic signatures of potential food resources, including biofilm, seston and both bulk wood and holocellulose extracted from bulk wood. 4. Wood-eating species had robust jaws specialized for gouging wood, d 13 C signatures consistent with assimilation of cellulosic wood carbon (not bulk wood carbon or lignin) and elevated d 15 N values (>5AE8&) relative to wood that were consistent with assimilation of N from intermediate microbial decomposers in the environment rather than direct assimilation of N from wood or from endosymbiotic N-fixers. Two non-wood-eating species occupied divergent regions of jaw functional morphospace, and isotopic signatures were consistent with assimilation of C from biofilm and seston, respectively, and N from enriched sources such as microbes, macroinvertebrates or seston. 5. Food resources associated with the surfaces of coarse woody debris in Neotropical rivers are partitioned among at least three guilds of loricariid consumers with divergent jaw morphologies specialized for wood gouging, surface grazing and macroinvertebrate probing. Direct consumption of morphic detritus by specialized Neotropical fishes constitutes a potentially important but poorly understood component of detritus processing and nutrient cycling in tropical rivers

Instream Flows Research and Validation Methodology Framework and Brazos Estuary Characterization: Brazos River and Associated Bay and Estuary System

Repor

Resolution of respect for Eric Rodger Pianka: 1939–2022

No abstract available