Mechanisms of carbohydrate‐fuelled ecological dominance in a tropical rainforest canopy‐foraging ant

1. Canopy‐foraging ants have carbohydrate‐rich diets and the stoichiometric excess of carbon may result in energetic allocation decisions that facilitate ecological dominance. 2. If dietary carbohydrates facilitate ecological dominance in canopy ants, then the mechanism for this relationship is unknown. 3. Four hypotheses were posit that may explain how a carbohydrate‐rich diet might facilitate ecological dominance in canopy ants: Aggressive Defense, Metabolic Fuel, Foraging Success, and Prey Acquisition. 4. To assess these hypotheses, experiments were conducted on the canopy‐foraging bullet ant, Paraponera clavata (Fabricius), an omnivorous species that demonstrates high variability in the relative contribution of carbohydrates to the diets of colonies. 5. No support was found for the Aggressive Defense, Metabolic Fuel and Prey Acquisition hypotheses. 6. The Foraging Success hypothesis was supported, as the proportion of nectar in the diet predicted the overall foraging success. 7. It was argued that there is no explicit advantage in the exploitation of nectar over other food resources, other than the fact that it is the most accessible food resource in the rainforest canopy.     

Cannibalism prevents evolutionary suicide of ontogenetic omnivores in life‐history intraguild predation systems

The majority of animal species are ontogenetic omnivores, that is, individuals of these species change or expand their diet during life. If small ontogenetic omnivores compete for a shared resource with their future prey, ecological persistence of ontogenetic omnivores can be hindered, although predation by large omnivores facilitates persistence. The coupling of developmental processes between different life stages might lead to a trade‐off between competition early in life and predation later in life, especially for ontogenetic omnivores that lack metamorphosis. By using bioenergetic modeling, we study how such an ontogenetic trade‐off affects ecological and evolutionary dynamics of ontogenetic omnivores. We find that selection toward increasing specialization of one life stage leads to evolutionary suicide of noncannibalistic ontogenetic omnivores, because it leads to a shift toward an alternative community state. Ontogenetic omnivores fail to re‐invade this new state due to the maladaptiveness of the other life stage. Cannibalism stabilizes selection on the ontogenetic trade‐off, prevents evolutionary suicide of ontogenetic omnivores, and promotes coexistence of omnivores with their prey. We outline how ecological and evolutionary persistence of ontogenetic omnivores depends on the type of diet change, cannibalism, and competitive hierarchy between omnivores and their prey.     

The omnivorous triggerfish Melichthys niger is a functional herbivore on an isolated Atlantic oceanic island

This study evaluated the functional role of the highly generalist omnivore Melichthys niger in the remote St. Peter and St Paul's Archipelago (SPSPA), Brazil, where grazing herbivorous fishes are very scarce. We analysed patterns of distribution from zero to 30 m deep during three time intervals during the day and sampled different aspects of their feeding behaviour, including diel feeding rate, feeding substrate and diet. The density of M. niger increased with depth (26–30 m) and decreased by the end of the day. Although M. niger did not present a typical herbivore diel feeding pattern, they targeted the epilithic algal matrix as their primary feeding substrate, ingesting predominantly algae and detritus. The characteristic Caulerpa racemosa var. peltata from SPSPA was ingested only as detached fronds. We suggest that in the isolated SPSPA, the single species M. niger may perform a unique role as a link between benthic primary production and higher levels. Further studies on the trophic ecology of omnivorous species are necessary to better understand their roles in a reef system, especially in impoverished areas where they are likely to play a crucial role.     

Morphofunctional study of the bill and hyoid apparatus of Momotus momota (Aves, Coraciiformes, Momotidae): implications for omnivorous feeding adaptation in motmots

The present study contrasts available biological data and results of morphofunctional analyses of the bill and hyoid apparatus in motmots. It shows that these omnivorous birds, which take relatively large food items, possess osteomuscular peculiarities that enable them to process these items as a whole in order to soften or cut them, and make them suited for easy ingestion. For that, they use the crenate edges of their rhamphotheca. Their jaws work as a highly mobile saw-like system. Their mutual movements, enhanced by the fact that particular dispositions of the hyoid apparatus rise the tongue and the supported items high up into buccal cavity, facilitate an effective clamping of items that can be moved along the jaws and be quite appropriately processed.     

Experimental demonstration of close-range olfaction and contact chemoreception in the Brazilian harvestman, Iporangaia pustulosa

We studied the ability to detect food by close-range olfaction and contact chemoreception in the harvestman Iporangaia pustulosa Mello-Leitão (Opiliones: Laniatores: Gonyleptidae). We first tested the reaction of individuals towards tasteless (pure agar), aversive (agar with salt), and food-intake stimulating substrates (agar with saccharose). Only the substrate containing saccharose was consumed. Contact (mainly with legs II) was necessary for detection of the agar and, before ingestion, the stimulus was always tapped with legs I. In the second experiment, we observed the behavior of individuals in an arena with a screened plastic box containing pieces of Tenebrio molitor L. (Coleoptera: Tenebrionidae) larvae. Individuals spent more time on the box containing food than on the control. In the third experiment, in an arena identical to that used in Experiment 2, we introduced a live but motionless T. molitor larva in the box. There was no difference between experimental and control treatments. We also observed the behavior of I. pustulosa in an arena containing live isopods. In first capture attempts, isopods were only detected upon contact, mainly with legs I. Our results suggest that (i) I. pustulosa is capable of detecting food only by its chemical properties; (ii) food with weak odor may not be detected by close-range olfaction; and (iii) legs I and II are important for food detection but, before ingestion, legs I are used to examine potential food items.     

What do tadpoles really eat? Assessing the trophic status of an understudied and imperiled group of consumers in freshwater habitats

1. Understanding the trophic status of consumers in freshwater habitats is central to understanding their ecological roles and significance. Tadpoles are a diverse and abundant component of many freshwater habitats, yet we know relatively little about their feeding ecology and true trophic status compared with many other consumer groups. While many tadpole species are labelled herbivores or detritivores, there is surprisingly little evidence to support these trophic assignments. 2. Here we discuss shortcomings in our knowledge of the feeding ecology and trophic status of tadpoles and provide suggestions and examples of how we can more accurately quantify their trophic status and ecological significance. 3. Given the catastrophic amphibian declines that are ongoing in many regions of the planet, there is a sense of urgency regarding this information. Understanding the varied ecological roles of tadpoles will allow for more effective conservation of remaining populations, benefit captive breeding programmes, and allow for more accurate predictions of the ecological consequences of their losses.     

Effects of omnivorous filter‐feeding fish and nutrient enrichment on the plankton community and water transparency of a tropical reservoir

1. The major aim of this study was to test the hypothesis that nutrient enrichment and the introduction of the Nile tilapia (Oreochromis niloticus), an exotic omnivorous filter‐feeding fish, operate interdependently to regulate plankton communities and water transparency of a tropical reservoir in the semi‐arid northeastern Brazil. 2. A field experiment was performed for 5 weeks in 20 enclosures (9.8 m³) to which four treatments were randomly allocated: tilapia addition (F), nutrient addition (N), tilapia and nutrient addition (F + N) and a control treatment with no tilapia or nutrient addition (C). A two‐way repeated measures anova was undertaken to test for time, tilapia and nutrient effects and their interactions on water transparency, total phosphorus and total nitrogen concentrations, phytoplankton biovolume and zooplankton biomass. 3. Nutrient addition had no effect except on rotifer biomass, but there were significant fish effects on the biomass of total zooplankton, copepod nauplii, rotifers, cladocerans and calanoid copepods and on the biovolume of total phytoplankton, large algae (GALD ≥ 50 μm), Bacillariophyta and Zygnemaphyceae and on Secchi depth. In addition, we found significant interaction effects between tilapia and nutrients on Secchi depth and rotifers. Overall, tilapia decreased the biomass of most zooplankton taxa and large algae (diatoms) and decreased water transparency, while nutrient enrichment increased the biomass of rotifers, but only in the absence of tilapia. 4. In conclusion, the influence of fish on the reservoir plankton community and water transparency was significant and even greater than that of nutrient loading. This suggests that biomanipulation of filter‐feeding tilapias may be of importance for water quality management of eutrophic reservoirs in tropical semi‐arid regions.     

Intermediate-consumer identity and resources alter a food web with omnivory

1. Omnivory is an important interaction that has been the centre of numerous theoretical and empirical studies in recent years. Most of these studies examine the conditions necessary for coexistence between an omnivore and an intermediate consumer. Trait variation in ecological interactions (competition and predator tolerance) among intermediate consumers has not been considered in previous empirical studies despite the evidence that variation in species-specific traits can have important community-level effects. 2. I conducted a multifactorial microcosm experiment using species from the Sarracenia purpurea phytotelmata community, organisms that inhabit the water collected within its modified leaves. The basal trophic level consisted of bacterial decomposers, the second trophic level (intermediate consumers) consisted of protozoa and rotifers, and the third trophic level (omnivore) were larvae of the pitcher plant mosquito Wyeomyia smithii. Trophic level number (1, 2 and 3), resources (low and high), omnivore density (low and high) and intermediate consumer (monoculture of five protozoa and rotifers) identity were manipulated. Abundance of the basal trophic level, intermediate consumers, and growth of the omnivore were measured, as well as time to extinction (intermediate consumers) and time to pupation (mosquito larvae). 3. The presence of different intermediate consumers affected both bacteria abundance and omnivore growth. At high resource levels, Poteriochromonas, Colpidium and Habrotrocha rosa reduced bacteria densities greater than omnivore reduction of bacteria. Mosquito larvae did not pupate at low resource levels except when Poteriochromonas and Colopoda were present as intermediate consumers. Communities with H. rosa were the only ones consistent with the prediction that omnivores should exclude intermediate consumers at high resources. 4. These results had mixed support for predictions from omnivory food web theory. Intermediate consumers responded and affected this community differently under different community structures and resource levels. Consequently, variation in species-specific traits can have important population- and community-level effects and needs to be considered in food webs with omnivory.     

The macroevolutionary relationship between diet and body mass across mammals

Body mass and diet are two fundamental ecological parameters that influence many other aspects of an animal's biology. Thus, the potential physiological and ecological processes linking size and diet have been the subject of extensive research, although the broad macroevolutionary relationship between the two traits remains largely unexplored phylogenetically. Using generalized Ornstein–Uhlenbeck models and data on over 1350 species of mammal, we reveal that evolutionary changes in body mass are consistently associated with dietary changes across mammals. Best‐fitting models find that herbivores are substantially heavier than other dietary groups and that omnivores are frequently intermediate in mass between herbivores and carnivores. Interestingly, although flying and swimming both place very different physical constraints on mass, bats still follow the general mammalian pattern but marine mammals do not. Such differences may be explained by reduced gravitational constraints on size in water along with ecological differences in food availability between aquatic and terrestrial realms, allowing marine carnivores to become the largest mammals on earth. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 173–184.     

Role of intraguild predation in aphidophagous guilds

The concept of intraguild predation (IGP) appeared in 1987–1989 to describe trophic interactions within a guild of arthropods inhabiting a sand dune desert: consumers B prey on consumers A and both of them prey on a common resource. Theory predicts that the two types of consumers should only coexist if consumer A is more efficient in the conversion of the common resource than B. As a consequence, this resource is more abundant in the presence than in the absence of intraguild predators. Such a theoretical prediction probably explains the vivid interest shown by ecologists involved in biological control for IGP. It is therefore not surprising that many papers report on IGP among natural enemies of aphids. A close examination of these reported cases indicates that they rarely fulfil the theoretical requirements for IGP. That is, guilds of aphidophagous insects are rarely the theatre of IGP but frequently of interspecific predation. This is confirmed by experimental assessment of the cost of attacking and eating intraguild prey instead of extraguild in ladybird beetles.