Fresh perspectives on the River Continuum Concept require trophic ecology approaches focussed on food web structure and energy mobilisation routes.

Stream-dwelling communities are expected to show a gradual replacement of the dominant feeding types following the type of resources found along the river continuum. Yet, the underlying longitudinal gradients in food web structure and energy flow-paths remain poorly understood. Here, I synthesise novel research on the River Continuum Concept (RCC) and identify promising areas for future research linked to longitudinal changes in food-chain length and energy mobilisation routes. For example, feeding links and connectance should reach maximum values in mid-order rivers and then decrease to river mouths following uncovered longitudinal diversity patterns. Regarding energy mobilisation routes, a gradual replacement in the food web fuelling between allochthonous (leaf litter) and autochthonous (periphyton) resources should be expected. Beyond longitudinal changes in primary basal resource to consumer paths, other allochthonous (e.g. riparian arthropod inputs) and autochthonous (e.g. fish prey) inputs subsidising higher level consumers may show longitudinal changes, that is, terrestrial invertebrates decreasing but piscivory increasing downstream. However, the role of these inputs, that can alter predator niche variation and have indirect community-based effects, on both food web structure and energy flow-paths along the river continuum is not clear yet. Incorporating energy mobilisation and food web structure into RCC principles is necessary for a broad understanding of ecosystem functioning and trophic diversity in riverine systems, driving the emergence of novel insights. How function and structure of riverine food webs adapt to longitudinal changes in physical and biological environments represent a challenge for next generation of stream ecologists.

Drivers of piscivory in a globally distributed aquatic predator (brown trout): a meta-analysis.

There is growing interest in the delineation of feeding patterns in animals, but little is known about the interaction of multiple explanatory factors across broad geographical scales. The goal of this study was to identify the factors that together determine population-level patterns in piscivory in a globally distributed aquatic predator, the brown trout (Salmo trutta). A meta-analysis of peer-reviewed studies revealed that the prevalence (frequency of occurrence, %) of piscivory increases from riverine to marine ecosystems, with fish community type and the size-structure (ontogeny) of brown trout populations being the key drivers. Thus, piscivory was related to ecosystem-specific differences in predator body size (increasing in populations with large individuals) and fish community configurations (increasing with fish species richness). Fish species richness imposes important limitations on (i.e. in low diversity scenarios) or facilitate (i.e. in high diversity scenarios) piscivory in brown trout populations, with a low prevalence expected in low-diversity fish communities. In fresh water, piscivory is higher in lentic than lotic ecosystems and, in the former, increases with latitude. Competition in multi-species systems is expected to be higher than in simpler systems because the size-structure and species composition of fish assemblages, explaining cross-ecosystem differences in piscivory.

Taxonomy-based differences in feeding guilds of fish.

It has been taken for granted that feeding guilds and behavior in animals are linked to the taxonomic relatedness of species, but empirical evidence supporting such relationship is virtually missing. To examine the importance of taxonomy on trophic ecology, I here present the first well-resolved dietary taxonomy analysis based on feeding guilds (predation, herbivory, and filtering) among families and genera within the fish order Perciformes. Taxonomic relatedness in feeding did not vary with ecosystem dimension (marine vs. freshwater). Although predation dominates among Perciformes fishes, this study shows that in most cases taxonomic units (family or genus) are composed by species with several feeding guilds. Related species are more similar in feeding compared with species that are taxonomically more distant, demonstrating that there is a greater variation of feeding guilds within families than genera. Thus, there is no consistency in feeding guilds between family- and genus-level taxonomy. This study provides empirical support for the notion that genera are more informative than families, underlining that family-level taxonomy should be avoided to infer feeding habits of fish species at finer taxonomic resolution. Thus, the choice of taxonomic resolution (family or genus level) in ecological studies is key to avoid information loss and misleading results. I conclude that high-rank taxonomic units (i.e., above the generic level) are not appropriate to test research hypotheses about the feeding of fish.

Feeding studies take guts - critical review and recommendations of methods for stomach contents analysis in fish.

Studies on the feeding ecology of fish are essential for exploring and contrasting trophic interactions and population and community dynamics within and among aquatic ecosystems. In this respect, many different methods have been adopted for the analysis of fish stomach contents. No consensus has, however, been reached for a standardised methodology despite that for several decades there has been an ongoing debate about which methodical approaches that should be preferred. Here, we critically review and scrutinise methods, addressing their strengths and weaknesses and emphasising inherent problems and possible pitfalls in their use. Although our critical assessment reveals that no completely ideal approach exists, appropriate and reliable procedures can be adopted through careful considerations and implementation. In particular, we advocate that different objectives require different methodical approaches and the choice of method should therefore be closely linked to the research questions that are addressed. For a standardisation of methods, we recommend a combination of the relative-fullness and presence-absence methods as the optimal approach for the commonly applied feeding studies addressing relative dietary composition in terms of prey diversity and abundance. Additionally, we recommend the gravimetric method for objectives related to the quantification of food consumption rates and the numerical method for prey selection studies. DNA-based dietary analysis provides a new and promising complementary approach to visual examination of stomach contents, although some technical challenges still exist. The suggested method standardisation facilitates comparisons across species, ecosystems and time and will enhance the applicability and benefits of fish feeding studies in trophic ecology research.

Suboptimal growth among individuals of brown trout (Salmo trutta) in a temperate river.

This study assessed growth of individually tagged brown trout Salmo trutta in a temperate system of north-west Spain (2010-2012). This study identified notable individual variation in fish growth with individuals growing sub-optimally compared with laboratory-based growth-model predictions in most cases (85.5% of individuals). The present observations of suboptimal growth need to be considered in view of intraspecific competition or limiting food resources instead of thermal regimes.

Causes and consequences of ontogenetic dietary shifts: a global synthesis using fish models.

Ontogenetic dietary shifts (ODSs), the changes in diet utilisation occurring over the life span of an individual consumer, are widespread in the animal kingdom. Understanding ODSs provides fundamental insights into the biological and ecological processes that function at the individual, population and community levels, and is critical for the development and testing of hypotheses around key concepts in trophic theory on model organisms. Here, we synthesise historic and contemporary research on ODSs in fishes, and identify where further research is required. Numerous biotic and abiotic factors can directly or indirectly influence ODSs, but the most influential of these may vary spatially, temporally and interspecifically. Within the constraints imposed by prey availability, we identified competition and predation risk as the major drivers of ODSs in fishes. These drivers do not directly affect the trophic ontogeny of fishes, but may have an indirect effect on diet trajectories through ontogenetic changes in habitat use and concomitant changes in prey availability. The synthesis provides compelling evidence that ODSs can have profound ecological consequences for fish by, for example, enhancing individual growth and lifetime reproductive output or reducing the risk of mortality. ODSs may also influence food-web dynamics and facilitate the coexistence of sympatric species through resource partitioning, but we currently lack a holistic understanding of the consequences of ODSs for population, community and ecosystem processes and functioning. Studies attempting to address these knowledge gaps have largely focused on theoretical approaches, but empirical research under natural conditions, including phylogenetic and evolutionary considerations, is required to test the concepts. Research focusing on inter-individual variation in ontogenetic trajectories has also been limited, with the complex relationships between individual behaviour and environmental heterogeneity representing a particularly promising area for future research.

Examining the link between dietary specialization and foraging modes of stream-dwelling brown trout Salmo trutta.

The aim of this study was to explore differences in dietary specialization across two foraging modes (benthic v. surface-drift foraging) of stream-dwelling brown trout Salmo trutta. The degree of inter-individual niche variation within each foraging mode was high, but the dietary specialization was maintained between foraging modes. This study supports the view that if aquatic invertebrates are more abundant and accessible than surface prey, the individuals will not specialize on surface prey (surface-drift foraging).

Necrosis avascular del cóndilo humeral: caso clínico-radiológico / Avascular necrosis of the capitellum humeri: A report of clinical-radiological case

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Prey diversity as a driver of resource partitioning between river-dwelling fish species.

Although food resource partitioning among sympatric species has often been explored in riverine systems, the potential influence of prey diversity on resource partitioning is little known. Using empirical data, we modeled food resource partitioning (assessed as dietary overlap) of coexisting juvenile Atlantic salmon (Salmo salar) and alpine bullhead (Cottus poecilopus). Explanatory variables incorporated into the model were fish abundance, benthic prey diversity and abundance, and several dietary metrics to give a total of seventeen potential explanatory variables. First, a forward stepwise procedure based on the Akaike information criterion was used to select explanatory variables with significant effects on food resource partitioning. Then, linear mixed-effect models were constructed using the selected explanatory variables and with sampling site as a random factor. Food resource partitioning between salmon and bullhead increased significantly with increasing prey diversity, and the variation in food resource partitioning was best described by the model that included prey diversity as the only explanatory variable. This study provides empirical support for the notion that prey diversity is a key driver of resource partitioning among competing species.

Community structure affects trophic ontogeny in a predatory fish.

While most studies have focused on the timing and nature of ontogenetic niche shifts, information is scarce about the effects of community structure on trophic ontogeny of top predators. We investigated how community structure affects ontogenetic niche shifts (i.e., relationships between body length, trophic position, and individual dietary specialization) of a predatory fish, brown trout (Salmo trutta). We used stable isotope and stomach content analyses to test how functional characteristics of lake fish community compositions (competition and prey availability) modulate niche shifts in terms of (i) piscivorous behavior, (ii) trophic position, and (iii) individual dietary specialization. Northern Scandinavian freshwater fish communities were used as a study system, including nine subarctic lakes with contrasting fish community configurations: (i) trout-only systems, (ii) two-species systems (brown trout and Arctic charr [Salvelinus alpinus] coexisting), and (iii) three-species systems (brown trout, Arctic charr, and three-spined sticklebacks [Gasterosteus aculeatus] coexisting). We expected that the presence of profitable small prey (stickleback) and mixed competitor-prey fish species (charr) supports early piscivory and high individual dietary specialization among trout in multispecies communities, whereas minor ontogenetic shifts were expected in trout-only systems. From logistic regression models, the presence of a suitable prey fish species (stickleback) emerged as the principal variable determining the size at ontogenetic niche shifts. Generalized additive mixed models indicated that fish community structure shaped ontogenetic niche shifts in trout, with the strongest positive relationships between body length, trophic position, and individual dietary specialization being observed in three-species communities. Our findings revealed that the presence of a small-sized prey fish species (stickleback) rather than a mixed competitor-prey fish species (charr) was an important factor affecting the ontogenetic niche-shift processes of trout. The study demonstrates that community structure may modulate the ontogenetic diet trajectories of and individual niche specialization within a top predator.

Síndrome del ducto pancreático desconectado / Disconnected pancreatic duct syndrome

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Food Web Topology in High Mountain Lakes.

Although diversity and limnology of alpine lake systems are well studied, their food web structure and properties have rarely been addressed. Here, the topological food webs of three high mountain lakes in Central Spain were examined. We first addressed the pelagic networks of the lakes, and then we explored how food web topology changed when benthic biota was included to establish complete trophic networks. We conducted a literature search to compare our alpine lacustrine food webs and their structural metrics with those of 18 published lentic webs using a meta-analytic approach. The comparison revealed that the food webs in alpine lakes are relatively simple, in terms of structural network properties (linkage density and connectance), in comparison with lowland lakes, but no great differences were found among pelagic networks. The studied high mountain food webs were dominated by a high proportion of omnivores and species at intermediate trophic levels. Omnivores can exploit resources at multiple trophic levels, and this characteristic might reduce competition among interacting species. Accordingly, the trophic overlap, measured as trophic similarity, was very low in all three systems. Thus, these alpine networks are characterized by many omnivorous consumers with numerous prey species and few consumers with a single or few prey and with low competitive interactions among species. The present study emphasizes the ecological significance of omnivores in high mountain lakes as promoters of network stability and as central players in energy flow pathways via food partitioning and enabling energy mobility among trophic levels.

Adaptive flexibility in the feeding behaviour of brown trout: optimal prey size.

BACKGROUND: Browntrout, Salmotrutta Linnaeus,1758, is a species of significant conservation and socio-economic importance. A consequence of this importance is the enormous amount of literature that has been published on the species in the last few decades. In general terms, brown trout has been considered as a size-selective predator, even though it is able to feed on a wide range of prey sizes. Nevertheless, there are still some gaps in our knowledge, for example the theoretical relationship between prey numbers and prey sizes eaten by the fish need to be addressed. This research aimed to study optimal prey size in the environment (benthos and drift) as well as the potential relationship between prey size and two other feeding variables (prey numbers and stomach fullness). Additionally, ontogenetic shifts in these variables were addressed. RESULTS: Brown trout showed a clear preference for 4- to 6-mm-length prey, although the use of prey larger than 10-mm length may be feasible. The similarity of the prey size frequency distribution between the environment (benthos and drift) and the diet in some cases was considerable (from 57.7% to 95.9%). Moreover, the results revealed that the feeding strategy can be related to prey size and the numbers of prey eaten by the brown trout; as food size decreased, prey numbers increased. On the contrary, the correlation between the average prey size and fish length was positive but statistically nonsignificant. A significant ontogenetic shift, in terms of prey size sorted by age classes, was found in only two of eight studied populations. No clear relationship between prey size and stomach fullness was found. CONCLUSIONS: The feeding strategy of this species is flexible and clearly influenced by the size frequency distribution of potential prey: trout fed on either small numbers of large prey or large numbers of small, and theoretically low energy, prey. Our approach covers a general subject in trophic ecology and animal behaviour that may be applicable to other fish species to improve our understanding of predator feeding behaviour.

[Seroprevalence of antibodies against Treponema pallidum, Toxoplasma gondii, rubella virus, hepatitis B and C virus, and HIV in pregnant women]. / Seroprevalencia de anticuerpos frente a Treponema pallidum, Toxoplasma gondii, virus de la rubéola, virus de la hepatitis B y C y VIH en mujeres gestantes.

INTRODUCTION: The prevalence of antibodies against Treponema pallidum, Toxoplasma gondii, rubella virus, hepatitis B virus (HBV), hepatitis C virus (HCV) and human immunodeficiency virus (HIV) was investigated in pregnant women. METHODS: With the use of several serological methods in samples from women who had their first obstetric visit in 2001, we studied the prevalence of serum antibodies against T. pallidum, T. gondii, rubella virus, HBV and HCV in 2,929 pregnant women, and anti-HIV antibodies in the 1,349 women agreeing to this test. RESULTS: Antibodies against T. pallidum were not detected in any case. HBsAg was found in 11 patients (0.4%), six of whom (54.5%) were not aware of their condition. The presence of anti-rubella antibodies was almost universal (99.95%). In the total population, 18.8% of patients had anti-T. gondii antibodies; only one had a serological profile suggesting acute toxoplasmosis. Among the 1,349 women studied, anti-HIV antibodies were detected in two intravenous drug abusers who were aware of their condition. Anti-HCV antibodies were found in 0.4% of the series, and 36.4% of the HCV-positive patients had no knowledge of their condition. CONCLUSIONS: Active infection by T. pallidum in pregnant women in Spain is currently exceptional. The level of immunization against rubella virus is excellent. Seropositivity to T. gondii is lower than rates reported in earlier studies. The prevalence of HBsAg and anti-HCV antibodies is around 0.4%, and seropositive status is often discovered in routine serological studies performed during pregnancy. HIV seropositivity is low, and the pregnant women included in this study were aware of their condition.