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Green lacewings are valuable predators, utilized in augmentative biological control against various agricultural pests. However, further studies are required to comprehend the performance of these predators when consuming natural prey. We investigated the capacity of Chrysoperla externa (Hagen) to utilize the following three distinct prey types: the pupae of the coffee leaf miner Leucoptera coffeella (Guérin-Mèneville & Perrottet), the eggs of the sugarcane borer Diatraea saccharalis (F.), and the eggs of the Mediterranean flour moth Ephestia kuehniella (Zeller). The first two of these species are naturally occurring prey found in field crops, while the last serves as a factitious prey species for the mass rearing of natural enemies. We hypothesized that the type of prey would differentially affect the life history and population-level parameters of C. externa. Laboratory experiments were conducted to compare the pre-imaginal survival and developmental times, adult longevity and reproduction, and population growth of C. externa when larvae were provided with each of the three prey items. Results indicated that C. externa utilized the two natural prey items, L. coffeella pupae and D. saccharalis eggs, for its development, reproduction, and population growth. However, larvae developed significantly faster and females exhibited higher reproductive parameters, including fecundity and daily oviposition, when consuming the factitious prey, E. kuehniella eggs. This resulted in a higher intrinsic rate of population increase, as well as shorter times for the population to double in size. Understanding the population dynamics of C. externa when consuming different prey items is crucial for optimizing their utilization in augmentative biological control programs.

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Among defenses against predation, chemical defenses are possibly the most studied. However, when addressing the effectiveness of those chemical defenses, previous studies did not include properties of the chemical substances themselves. Lipophilicity, for instance, may facilitate crossing membranes, and boiling point may define the duration of the substances in the air. Moreover, other variables may also be relevant: the predator taxon; the prey model chosen to conduct experiments; whether the prey is presented grouped or not in experiments; and whether the chemical defense is a mixture of many substances or only one. To understand how those factors influence chemical defenses' effectiveness, we conducted a multilevel meta-analysis with 43 studies (127 effect sizes), accounting for different types of dependence. We used Akaike Information Criterion (AICc) to select the best model. The model with the lowest AICc value included only the boiling point, which defines how quickly a chemical substance volatilizes. This model indicated that the most effective chemical defenses had lower boiling point values, i.e., higher volatility. Moreover, we did not find chemicals with very low boiling points, suggesting there might be an optimum range of volatility. Other models, including the intercept-only model, were also recovered among the best models, therefore further studies are needed to confirm the relationship between volatility and chemical defenses' effectiveness. Our results highlight the value of incorporating physicochemical properties in the ecological and evolutionary study of chemical defense.

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Visual animal communication, whether to the same or to other species, is largely conducted through dynamic and colourful signals. For a signal to be effective, the signaller must capture and retain the attention of the receiver. Signal efficacy is also dependent on the sensory limitations of the receiver. However, most signalling studies consider movement and colour separately, resulting in a partial understanding of the signal in question. We explored the structure and function of predator-prey signalling in the jumping spider-tephritid fly system, where the prey performs a wing waving display that deters an attack from the predator. Using a custom-built spider retinal tracker combined with visual modelling, as well as behavioural assays, we studied the effect of fly wing movement and colour on the jumping spider's visual system. We show that jumping spiders track their prey less effectively during wing display and this can be attributed to a series of fluctuations in chromatic and achromatic contrasts arising from the wing movements. These results suggest that displaying flies deter spider attacks by manipulating the movement biases of the spider's visual system. Our results emphasise the importance of receiver attention on the evolution of interspecific communication.

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The emphasis on mechanisms governing the interaction among predators (e.g. cooperation, competition or intraguild predation) has driven the understanding of multiple-predator effects on prey survival and dynamics. However, overwhelming evidence shows that prey can adaptively respond to predators, exhibiting multiple defensive phenotypes to cope with predation. Nevertheless, there is still a relatively scarce theory connecting the emergence of prey defences in complex multi-predator scenarios and their ecological consequences. Using a mathematical approach, we evaluated the prevalence of defended prey phenotypes as a function of predator-induced mortality in a two-predator system, and how prey and phenotype dynamics affect trophic cascades. We also evaluated such responses when prey manifests a general defence against both predators (i.e. risk reducing) or a specialized defence against one predator at the expense of defence against the other predator (i.e. risk trade-off), and when such phenotypes induce fitness and foraging costs. We showed that the emergence of defended phenotypes under multiple predators depends on predator-induced mortality rates, the magnitude of phenotype costs and the effect of the defensive phenotype on the performance of all predators. Risk-reducing phenotypes enhance prioritized responses to predators with high killing rates, but prioritized responses are diminished when prey manifest risk trade-off phenotypes. Finally, we showed that resource abundance across the predation gradient directly depends on the prevalence of certain prey phenotypes and their effect on foraging costs. Ultimately, our results depict the implications of prey defences on prey and basal resources abundance in a multiple predators' environment, highlighting the role of the identity of defensive strategies in mediating the strength and nature of trophic cascades, via consumptive or non-consumptive effects.

A ênfase nos mecanismos que governam a interação entre predadores (por exemplo, cooperação, competição ou predação intra-guilda) tem impulsionado a compreensão dos efeitos de múltiplos predadores na sobrevivência e dinâmica de presas. No entanto, fortes evidências mostram que as presas podem responder de forma adaptativa aos predadores, exibindo vários fenótipos de defesa para lidar com a predação. No entanto, ainda há uma teoria relativamente escassa conectando a manifestação de defesas em presas em cenários com múltiplos predadores e suas consequências ecológicas. Usando uma abordagem matemática, avaliamos a prevalência de fenótipos de defesa de presas em função da mortalidade induzida por predadores em um sistema de dois predadores, e como a dinâmica de presas e dos fenótipos afeta a cascata trófica. Também avaliamos tais respostas quando a presa manifesta uma defesa geral contra ambos os predadores (ou seja, redução de risco) ou uma defesa especializada contra um predador em detrimento da defesa contra o outro predador (ou seja, trade-off de risco), e quando tais fenótipos induzem custos ao fitness e ao forrageamento. Nós mostramos que a manifestação de fenótipos de defesa sob múltiplos predadores depende das taxas de mortalidade induzidas pelo predador, da magnitude dos custos do fenótipo e do efeito do fenótipo no desempenho dos predadores. Os fenótipos de redução de risco aumentam as respostas priorizadas aos predadores com altas taxas de predação, mas as respostas priorizadas são reduzidas quando as presas manifestam fenótipos de trade-off de risco. Finalmente, mostramos que a abundância de recursos ao longo do gradiente de predação depende diretamente da prevalência de determinados fenótipos e seus efeitos no forrageamento da presa. Em última análise, nossos resultados retratam as implicações das defesas contra predadores na abundância de presas e recursos basais em um ambiente com múltiplos predadores, destacando o papel da identidade de estratégias de defesa na mediação da força e natureza das cascatas tróficas, via efeitos de consumo ou comportamentais.

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Amphibians breeding in aquatic environments may encounter a myriad of threats during their life cycle. One species known to prey on native amphibians in aquatic habitats is the invasive North American bullfrog Lithobates catesbeianus, which, besides being a voracious predator and competitor, often acts as a pathogen carrier and disease superspreader because it tolerates high infection loads of the frog-killing fungus Batrachochytrium dendrobatidis (Bd). Here, we hypothesized that the presence of the bullfrogs in microcosms should either (1) decrease Bd disease severity in native frog species by discouraging them from using the aquatic environment, or (2) increase the mortality of the native species. We tested these 2 mutually exclusive hypotheses by co-housing the snouted treefrog Scinax x-signatus (native to our study area) with L. catesbeianus in the laboratory, exposing them to Bd, and using qPCR analysis to quantify the resulting Bd infection loads in the native frogs. Our experiment had the following replicated treatments: (1) native-only treatment (3 individuals of S. x-signatus), (2) native-predominant treatment (2 S. x-signatus + 1 L. catesbeianus), and (3) exotic-predominant treatment (1 S. x-signatus + 2 L. catesbeianus). We found that Bd infection loads in the native S. x-signatus were highest in the native-only treatment, and lowest in the exotic-predominant treatment, indicating that bullfrogs may discourage native frogs from occupying the aquatic habitat, thus reducing encounter rates between native frogs and the waterborne pathogen. This effect could be driven by the bullfrogs' predatory behavior and their high philopatry to aquatic habitats. Our results highlight that predation risk adds to the complexity of host-species interactions in Bd epidemiology.

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BACKGROUND: Scorpionism is a worldwide problem that has already made thousands of victims, and multi-disciplinary approaches for controlling their populations are to be more successful. Hens are often mentioned as tools for controlling scorpions; however, systematic/experimental behavioral studies are not available. Moreover, there is no systematic information on the effect of scorpion venoms on hens. Using the venomous yellow scorpion Tityus serrulatus, the present study aimed to clarify the following aspects: (1) voracity of hens, (2) how hens react when stung, (3) the effect of scorpion stings on hen behavior during attacks, and (4) hen survivorship after feeding on scorpions. METHODS: We attracted hens with corn powder, offered them scorpions and then recorded the hen-scorpion interaction. To test the effects of the sting we manually removed the scorpion's telson. RESULTS: We found that some hens ate up to six scorpions within minutes. By means of an ethogram and drawings, we showed that they exhibited several aversive behaviors when capturing scorpions. Removal of the scorpion telson stopped the aversive reactions, which was not observed in the control group. Finally, hens did not exhibit atypical behaviors after 1, 7 and 30 days and were all alive after 30 days. CONCLUSION: This is the first empirical and video recorded study providing evidence that hens are clearly affected by scorpion venom but do not die. Therefore, they may have potential to be used in biological control of these arthropods.

RESUMO

Scorpionism is a worldwide problem that has already made thousands of victims, and multi-disciplinary approaches for controlling their populations are to be more successful. Hens are often mentioned as tools for controlling scorpions; however, systematic/experimental behavioral studies are not available. Moreover, there is no systematic information on the effect of scorpion venoms on hens. Using the venomous yellow scorpion Tityus serrulatus, the present study aimed to clarify the following aspects: (1) voracity of hens, (2) how hens react when stung, (3) the effect of scorpion stings on hen behavior during attacks, and (4) hen survivorship after feeding on scorpions. Methods: We attracted hens with corn powder, offered them scorpions and then recorded the hen-scorpion interaction. To test the effects of the sting we manually removed the scorpion's telson. Results: We found that some hens ate up to six scorpions within minutes. By means of an ethogram and drawings, we showed that they exhibited several aversive behaviors when capturing scorpions. Removal of the scorpion telson stopped the aversive reactions, which was not observed in the control group. Finally, hens did not exhibit atypical behaviors after 1, 7 and 30 days and were all alive after 30 days. Conclusion: This is the first empirical and video recorded study providing evidence that hens are clearly affected by scorpion venom but do not die. Therefore, they may have potential to be used in biological control of these arthropods.(AU)

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Abstract Background: Scorpionism is a worldwide problem that has already made thousands of victims, and multi-disciplinary approaches for controlling their populations are to be more successful. Hens are often mentioned as tools for controlling scorpions; however, systematic/experimental behavioral studies are not available. Moreover, there is no systematic information on the effect of scorpion venoms on hens. Using the venomous yellow scorpion Tityus serrulatus, the present study aimed to clarify the following aspects: (1) voracity of hens, (2) how hens react when stung, (3) the effect of scorpion stings on hen behavior during attacks, and (4) hen survivorship after feeding on scorpions. Methods: We attracted hens with corn powder, offered them scorpions and then recorded the hen-scorpion interaction. To test the effects of the sting we manually removed the scorpions telson. Results: We found that some hens ate up to six scorpions within minutes. By means of an ethogram and drawings, we showed that they exhibited several aversive behaviors when capturing scorpions. Removal of the scorpion telson stopped the aversive reactions, which was not observed in the control group. Finally, hens did not exhibit atypical behaviors after 1, 7 and 30 days and were all alive after 30 days. Conclusion: This is the first empirical and video recorded study providing evidence that hens are clearly affected by scorpion venom but do not die. Therefore, they may have potential to be used in biological control of these arthropods.

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Turbidity plays an important role in aquatic predator-prey interactions. Increases in turbidity are expected to reduce prey capture rates, especially for visually oriented predators. However, there is also evidence indicating that turbidity may have little or no effect on predation rates. Here, we conducted a systematic review and meta-analysis of the relationship between turbidity and capture rate. We explored possible sources of heterogeneity in the effect sizes (capture strategy, predator's body size, relative eye size and turbidity range in the experiments) while controlling for the dependence among effects sizes and phylogenetic relationships among predator species. We found a consistent negative effect of turbidity on prey capture and that turbidity range (manipulated in the experiments) was the main factor accounting for between-study variation in effect sizes. Also, capture rates of both visually and non-visually oriented predators decreased with an increase in turbidity. In addition, for visually oriented fish predators, the relative eye size did not influence the effect sizes. Despite the paucity of studies for some groups of aquatic predators (mainly in tropical regions), we provide corroborative evidence that turbidity is a critical environmental factor controlling predator-prey interactions. This result is especially relevant considering that changes in turbidity is a human-induced pervasive environmental alteration resulted from, among other mechanisms, runoff after deforestation, eutrophication or oligotrophication in reservoir cascades, which imply changes in predator-prey interactions.

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Bioluminescence, which occurs in approximately 80% of the world's mesopelagic fauna, can take the form of a low-intensity continuous glow (e.g. for counter-illumination or signalling) or fast repetitions of brighter anti-predatory flashes. The southern elephant seal (SES) is a major consumer of mesopelagic organisms, in particular the abundant myctophid fish, yet the fine-scale relationship between this predator's foraging behaviour and bioluminescent prey remains poorly understood. We hypothesised that brief, intense light emissions should be closely connected with prey strikes when the seal is targeting bioluminescent prey that reacts by emitting anti-predator flashes. To test this, we developed a biologging device containing a fast-sampling light sensor together with location and movement sensors to measure simultaneously anti-predator bioluminescent emissions and the predator's attack motions with a 20 ms resolution. Tags were deployed on female SES breeding at Kerguelen Islands and Península Valdés, Argentina. In situ light levels in combination with duration of prey capture attempts indicated that seals were targeting a variety of prey types. For some individuals, bioluminescent flashes occurred in a large proportion of prey strikes, with the timing of flashes closely connected with the predator's attack motion, suggestive of anti-predator emissions. Marked differences across individuals and location indicate that SES do exploit bioluminescent organisms but the proportion of these in the diet varies widely with location. The combination of wideband light and acceleration data provides new insight into where and when different prey types are encountered and how effectively they might be captured.

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Diaphorina citri Kuwayama is the vector of the pathogenic bacteria Candidatus Liberibacter spp., the causative agent of Huanglongbing (HLB), the most serious disease of citrus worldwide. Because predatory insects have been historically neglected in biological control programs for D. citri, the impact of generalist predators on D. citri population densities is little understood. A useful tool to evaluate the dynamics of predator-prey interactions is molecular analysis of predators' gut content. We constructed a specific molecular marker to detect D. citri DNA in the gut content of predator insects, for use in estimating the predation rate of field-collected predators in citrus orchards on D. citri. Bioassays of the DNA half-life detection time were carried out with two predatory species, the ladybird beetle Hippodamia convergens Guérin-Méneville and the lacewing Chrysoperla externa (Hagen). The D. citri DNA half-life detection time (DT50) was 6.11 h for H. convergens and 5.46 h for C. externa. One hundred and seven field-collected predators were used for gut-content analysis (52 larvae/adults of ladybirds and 55 larvae of lacewings). The assays showed that 17.3% of ladybirds but no lacewings tested positive for D. citri DNA. These results show that generalist predators can contribute to biological control of D. citri and should be considered for use in pest management programs in citrus orchards.

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ABSTRACT Neotropical amphibians play important roles as preys and predators in freshwater and terrestrial ecosystems. The subfamily Pseudinae includes small and medium-sized frogs within three genera representing 13 valid species. Most published records of predation on Pseudinae frogs are anecdotic and scarce. Herein, we provide five new reports of predation and presenting a detailed literature review on Pseudinae predation, with 15 studies published between 1983-2017. Pseudinae species were preyed at both day and night by a wide variety of predators, principally birds. Adults were preyed upon more frequently than juveniles and tadpoles. In the present study, most predators were diurnal, with birds accounting for most records. A variety of invertebrates prey on anurans, but water bugs and spiders are the most common ones. In the present study, water bugs comprised 75 % of the Pseudinae predation records by invertebrates. However, anuran predation by invertebrates remains poorly documented. Thus, the description of new cases of predation accompanied by a review of the data available in the literature is crucial to understanding Neotropical food webs.

RESUMEN Los anfibios neotropicales desempeñan papeles importantes como depredadores y presas en los ecosistemas dulce acuícolas y terrestres. La subfamilia Pseudinae incluye ranas pequeñas y medianas, distribuidas en tres géneros y representando 13 especies válidas. Los registros de depredación de Pseudinae son escasos y anecdóticos. Por lo tanto, el conocimiento de nuevos casos puede mejorar nuestra comprensión de las relaciones depredador-presa entre estas ranas y su papel en la cadena trófica. Presentamos cinco nuevos registros de depredación y revisamos los casos de depredación de la literatura, que incluyen 15 estudios publicados entre 1983 y 2017. Las especies de Pseudinae son depredadas, tanto durante el día como en la noche, por una gran variedad de depredadores, principalmente aves. Los adultos son más frecuentemente depredados que los juveniles y los renacuajos. En el presente estudio, las chinches de agua representan 75 % de los registros de depredación de Pseudinae por invertebrados. Sin embargo, depredación de anuros por invertebrados permanece poco documentada. Por lo tanto, la descripción de nuevos casos de depredación, junto a una revisión de los datos disponibles en la literatura es crucial para entender redes tróficas neotropicales.

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Theories involving niche diversification to explain high levels of tropical diversity propose that species are more likely to co-occur if they partition at least one dimension of their ecological niche space. Yet, numerous species appear to have widely overlapping niches based upon broad categorizations of resource use or functional traits. In particular, the extent to which food partitioning contributes to species coexistence in hyperdiverse tropical ecosystems remains unresolved. Here, we use a molecular approach to investigate inter- and intraspecific dietary partitioning between two species of damselfish (Dascyllus flavicaudus, Chromis viridis) that commonly co-occur in branching corals. Species-level identification of their diverse zooplankton prey revealed significant differences in diet composition between species despite their seemingly similar feeding strategies. Dascyllus exhibited a more diverse diet than Chromis, whereas Chromis tended to select larger prey items. A large calanoid copepod, Labidocera sp., found in low density and higher in the water column during the day, explained more than 19% of the variation in dietary composition between Dascyllus and Chromis. Dascyllus did not significantly shift its diet in the presence of Chromis, which suggests intrinsic differences in feeding behaviour. Finally, prey composition significantly shifted during the ontogeny of both fish species. Our findings show that levels of dietary specialization among coral reef associated species have likely been underestimated, and they underscore the importance of characterizing trophic webs in tropical ecosystems at higher levels of taxonomic resolution. They also suggest that niche redundancy may not be as common as previously thought.

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Many animals use body coloration as a strategy to communicate with conspecifics, prey, and predators. Color is a trade-off for some species, since they should be visible to conspecifics but cryptic to predators and prey. Some flower-dwelling predators, such as crab spiders, are capable of choosing the color of flowers where they ambush flower visitors and pollinators. In order to avoid being captured, visitors evaluate flowers visually before landing. The crab spider Mecaphesa dubia is a polymorphic species (white/purple color morphs), which inhabits the flower heads of a dune plant, Palafoxia lindenii. Using full-spectrum photography of spiders and flowers, we evaluated how honeybees perceived the spiders at different distances. Using visual modeling, we obtained the chromatic and achromatic contrasts of the spiders on flower heads as perceived by honeybees. Purple morphs were found mainly on the receptacle area and white morphs were equally likely to be found in the flowers and receptacle. According to theoretical modeling, white morphs were visible to honeybees from a distance of 10 cm in receptacle area but appeared to be cryptic in the flower area. Purple morphs were cryptic on the receptacle and less so when they were on the flowers. Spiders on flower heads are predicted to be more easily detected by honeybees using chromatic contrast. Our study shows that the conspicuousness of flower dwelling spiders to honeybees depends on the color morph, the distance of observation, and the position of spider on the flower head.

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Habitat complexity influences species diversity and regulates trophic interactions, mostly by increasing resource partitioning within habitats and providing refuge for prey. The influence of habitat complexity on more than two trophic levels is not well understood, mainly because behavioral modifications of prey and predator may influence the outcome of trophic interactions. Thus, we conducted a two-factor experiment with a three-level trophic chain: a piscivorous fish [Hoplerythrinus unitaeniatus (Spix & Agassiz 1829)], an invertivorous fish (Moenkhausia forestii Benine, Mariguela & C. de Oliveira, 2009) and an aquatic macroinvertebrate (Chironomidae larvae). We measured prey consumption in low, intermediate and high habitat complexity, provided by submerged macrophyte densities, in the presence and the absence of the piscivore, intending to test the hypothesis that higher habitat complexities decrease predators foraging success in different trophic levels. We calculated the percentage of consumed prey in all treatment combinations. There was no significant effect of habitat complexity on prey consumption for neither the piscivorous nor the invertivorous fish, but a positive correlation was found between the percentages of consumed prey by both the piscivore and the invertivore. Observed modifications in the foraging behavior of the piscivore may have resulted in similar prey consumptions in low and high macrophyte densities. Moreover, more active M. forestii could have suffered a higher predation pressure by H. unitaeniatus, resulting in the positive correlation found. We conclude that behavior patterns in different habitat complexities possibly influenced predation rates in the three experimental trophic levels.

A complexidade de habitat influencia a diversidade de espécies e regula interações tróficas, principalmente por possibilitar a partição de recurso nos habitats e fornecer refúgio para presas. A influência da complexidade de habitat sob mais de dois níveis tróficos não é bem compreendida, especialmente porque modificações comportamentais das presas e dos predadores podem influenciar o resultado das interações tróficas. Assim, nós conduzimos um experimento bifatorial com uma cadeia trófica de três níveis: um peixe piscívoro [Hoplerythrinus unitaeniatus (Spix & Agassiz 1829)], um peixe invertívoro (Moenkhausia forestii Benine, Mariguela & C. de Oliveira, 2009) e um macroinvertebrados aquático (larvas de Chironomidae). Mensuramos o consumo de presas em complexidades de habitat baixa, intermediária e alta, dada por diferentes densidades de macrófitas submersas, na presença e ausência do piscívoro, com o intuito de testar a hipótese de que complexidades de habitat mais altas diminuem o sucesso de forrageio de predadores em diferentes níveis tróficos. Calculamos a porcentagem de presas consumidas em todas as combinações de tratamentos. Não houve efeito significativo da complexidade de habitat no consumo de presas para o peixe piscívoro nem para o peixe invertívoro, mas uma correlação positiva foi encontrada entre as porcentagens de presas consumidas pelo piscívoro e pelo invertívoro. Modificações observadas no comportamento de forrageio do piscívoro podem ter resultado em consumo de presas similar em densidades baixas e altas de macrófitas. Além disso, indivíduos de M. forestii com maior taxa de forrageamento podem ter sofrido maior pressão de predação por H. unitaeniatus, resultando na correlação positiva encontrada. Concluímos que padrões comportamentais em diferentes complexidades de habitat possivelmente influenciaram as taxas de predação nos três níveis tróficos experimentais.

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ABSTRACT Habitat complexity influences species diversity and regulates trophic interactions, mostly by increasing resource partitioning within habitats and providing refuge for prey. The influence of habitat complexity on more than two trophic levels is not well understood, mainly because behavioral modifications of prey and predator may influence the outcome of trophic interactions. Thus, we conducted a two-factor experiment with a three-level trophic chain: a piscivorous fish [Hoplerythrinus unitaeniatus (Spix & Agassiz 1829)], an invertivorous fish (Moenkhausia forestii Benine, Mariguela & C. de Oliveira, 2009) and an aquatic macroinvertebrate (Chironomidae larvae). We measured prey consumption in low, intermediate and high habitat complexity, provided by submerged macrophyte densities, in the presence and the absence of the piscivore, intending to test the hypothesis that higher habitat complexities decrease predators foraging success in different trophic levels. We calculated the percentage of consumed prey in all treatment combinations. There was no significant effect of habitat complexity on prey consumption for neither the piscivorous nor the invertivorous fish, but a positive correlation was found between the percentages of consumed prey by both the piscivore and the invertivore. Observed modifications in the foraging behavior of the piscivore may have resulted in similar prey consumptions in low and high macrophyte densities. Moreover, more active M. forestii could have suffered a higher predation pressure by H. unitaeniatus, resulting in the positive correlation found. We conclude that behavior patterns in different habitat complexities possibly influenced predation rates in the three experimental trophic levels.

RESUMO A complexidade de habitat influencia a diversidade de espécies e regula interações tróficas, principalmente por possibilitar a partição de recurso nos habitats e fornecer refúgio para presas. A influência da complexidade de habitat sob mais de dois níveis tróficos não é bem compreendida, especialmente porque modificações comportamentais das presas e dos predadores podem influenciar o resultado das interações tróficas. Assim, nós conduzimos um experimento bifatorial com uma cadeia trófica de três níveis: um peixe piscívoro [Hoplerythrinus unitaeniatus (Spix & Agassiz 1829)], um peixe invertívoro (Moenkhausia forestii Benine, Mariguela & C. de Oliveira, 2009) e um macroinvertebrados aquático (larvas de Chironomidae). Mensuramos o consumo de presas em complexidades de habitat baixa, intermediária e alta, dada por diferentes densidades de macrófitas submersas, na presença e ausência do piscívoro, com o intuito de testar a hipótese de que complexidades de habitat mais altas diminuem o sucesso de forrageio de predadores em diferentes níveis tróficos. Calculamos a porcentagem de presas consumidas em todas as combinações de tratamentos. Não houve efeito significativo da complexidade de habitat no consumo de presas para o peixe piscívoro nem para o peixe invertívoro, mas uma correlação positiva foi encontrada entre as porcentagens de presas consumidas pelo piscívoro e pelo invertívoro. Modificações observadas no comportamento de forrageio do piscívoro podem ter resultado em consumo de presas similar em densidades baixas e altas de macrófitas. Além disso, indivíduos de M. forestii com maior taxa de forrageamento podem ter sofrido maior pressão de predação por H. unitaeniatus, resultando na correlação positiva encontrada. Concluímos que padrões comportamentais em diferentes complexidades de habitat possivelmente influenciaram as taxas de predação nos três níveis tróficos experimentais.

RESUMO

Habitat complexity influences species diversity and regulates trophic interactions, mostly by increasing resource partitioning within habitats and providing refuge for prey. The influence of habitat complexity on more than two trophic levels is not well understood, mainly because behavioral modifications of prey and predator may influence the outcome of trophic interactions. Thus, we conducted a two-factor experiment with a three-level trophic chain: a piscivorous fish [Hoplerythrinus unitaeniatus (Spix & Agassiz 1829)], an invertivorous fish (Moenkhausia forestii Benine, Mariguela & C. de Oliveira, 2009) and an aquatic macroinvertebrate (Chironomidae larvae). We measured prey consumption in low, intermediate and high habitat complexity, provided by submerged macrophyte densities, in the presence and the absence of the piscivore, intending to test the hypothesis that higher habitat complexities decrease predators foraging success in different trophic levels. We calculated the percentage of consumed prey in all treatment combinations. There was no significant effect of habitat complexity on prey consumption for neither the piscivorous nor the invertivorous fish, but a positive correlation was found between the percentages of consumed prey by both the piscivore and the invertivore. Observed modifications in the foraging behavior of the piscivore may have resulted in similar prey consumptions in low and high macrophyte densities. Moreover, more active M. forestii could have suffered a higher predation pressure by H. unitaeniatus, resulting in the positive correlation found. We conclude that behavior patterns in different habitat complexities possibly influenced predation rates in the three experimental trophic levels.(AU)

A complexidade de habitat influencia a diversidade de espécies e regula interações tróficas, principalmente por possibilitar a partição de recurso nos habitats e fornecer refúgio para presas. A influência da complexidade de habitat sob mais de dois níveis tróficos não é bem compreendida, especialmente porque modificações comportamentais das presas e dos predadores podem influenciar o resultado das interações tróficas. Assim, nós conduzimos um experimento bifatorial com uma cadeia trófica de três níveis: um peixe piscívoro [Hoplerythrinus unitaeniatus (Spix & Agassiz 1829)], um peixe invertívoro (Moenkhausia forestii Benine, Mariguela & C. de Oliveira, 2009) e um macroinvertebrados aquático (larvas de Chironomidae). Mensuramos o consumo de presas em complexidades de habitat baixa, intermediária e alta, dada por diferentes densidades de macrófitas submersas, na presença e ausência do piscívoro, com o intuito de testar a hipótese de que complexidades de habitat mais altas diminuem o sucesso de forrageio de predadores em diferentes níveis tróficos. Calculamos a porcentagem de presas consumidas em todas as combinações de tratamentos. Não houve efeito significativo da complexidade de habitat no consumo de presas para o peixe piscívoro nem para o peixe invertívoro, mas uma correlação positiva foi encontrada entre as porcentagens de presas consumidas pelo piscívoro e pelo invertívoro. Modificações observadas no comportamento de forrageio do piscívoro podem ter resultado em consumo de presas similar em densidades baixas e altas de macrófitas. Além disso, indivíduos de M. forestii com maior taxa de forrageamento podem ter sofrido maior pressão de predação por H. unitaeniatus, resultando na correlação positiva encontrada. Concluímos que padrões comportamentais em diferentes complexidades de habitat possivelmente influenciaram as taxas de predação nos três níveis tróficos experimentais.(AU)

Assuntos

RESUMO

Animals from a wide range of taxonomic groups are capable of colour change, of which camouflage is one of the main functions. A considerable amount of past work on this subject has investigated species capable of extremely rapid colour change (in seconds). However, relatively slow colour change (over hours, days, weeks and months), as well as changes arising via developmental plasticity are probably more common than rapid changes, yet less studied. We discuss three key areas of colour change and camouflage. First, we review the mechanisms underpinning colour change and developmental plasticity for camouflage, including cellular processes, visual feedback, hormonal control and dietary factors. Second, we discuss the adaptive value of colour change for camouflage, including the use of different camouflage types. Third, we discuss the evolutionary-ecological implications of colour change for concealment, including what it can tell us about intraspecific colour diversity, morph-specific strategies, and matching to different environments and microhabitats. Throughout, we discuss key unresolved questions and present directions for future work, and highlight how colour change facilitates camouflage among habitats and arises when animals are faced with environmental changes occurring over a range of spatial and temporal scales.This article is part of the themed issue 'Animal coloration: production, perception, function and application'.

Assuntos

RESUMO

Food webs are not static entities; consumer resource interactions vary in both time and space, which complicates depiction and comparisons of food web structures. We estimated fish assemblage structure and diets in two clear-water streams in the Venezuelan Llanos region (Charcote and Charcotico) and constructed trophic networks (sub-webs defined by fishes as the principal consumers) during four periods of the annual flood pulse. As stream conditions changed from high-water to low-water, we hypothesized that: 1) the piscivore-non-piscivore ratio would increase; 2) dietary diversity would decrease; 3) interspecific dietary overlap would decline; 4) fewer allochthonous food items would be consumed; and 5) food-web connectance would increase. The piscivore-non-piscivore abundance ratio was higher in both streams during the low-water period. Dietary diversity declined as water levels dropped and availability of aquatic habitats and resources declined, but interspecific dietary overlap was not lower. Contrary to our hypothesis, average interspecific dietary overlap increased at Charcote as the dry season progressed, even though dietary overlap among species was significantly lower than expected by chance. We did not find strong support for our hypotheses regarding seasonal patterns of consumption of allochthonous resources and food web connectance, both of which revealed little seasonal variation.(AU)

Redes alimentares não são entidades estáticas; interações entre consumidores e recursos variam no tempo e no espaço, o que complica as representações das estruturas de redes alimentares. Nós estimamos a estrutura da assembléia de peixes e dieta em dois riachos de água clara na região venezuelana dos Llanos (Charcote e Charcotico) e construímos redes tróficas (sub-redes definidas por peixes como os principais consumidores) para quatro períodos do pulso anual de inundação. À medida que as condições dos riachos mudam de águas altas para águas baixas, nós hipotetizamos que: 1) a razão piscívoros e não piscívoros irá aumentar; 2) a diversidade da dieta irá diminuir; 3) a sobreposição alimentar interespecífica irá diminuir; 4) menos itens alimentares alóctones serão consumidos; e 5) a conectância da teia alimentar irá aumentar. A razão da abundância de piscívoros e não piscívoros foi maior em ambos riachos durante a estação de águas baixas. A diversidade da dieta declinou à medida que as águas baixavam e a disponibilidade de habitats aquáticos e recursos declinavam, mas a sobreposição alimentar interespecífica não foi menor. Contrária à nossa hipótese, a média de sobreposição alimentar interespecífica aumentou no Charcote à medida que a estação cheia progrediu, mesmo com a sobreposição alimentar significativamente menor do que o esperado ao acaso. Não encontramos forte suporte para nossas hipóteses relacionadas aos padrões sazonais de consumo de recursos alóctones e conectância da cadeia trófica, os quais revelaram pouca variação sazonal.(AU)

RESUMO

The hunting tactics of lemon sharks, Negaprion brevirostris, are described from underwater and cliff-top observations in the Fernando de Noronha Archipelago, western equatorial Atlantic, Brazil. Two main tactics were observed in the shallow waters of sandy beaches and reefs environments: (i) “substrate inspection” of crevices and holes over rocky and reef bottoms, and (ii) “sardine blitz”, which refer to striking schools of fishes (mainly sardines) in the surf zone. The first tactic was restricted to juveniles up to 2 m of total length, whereas subadult and adult sharks with total length larger than 2 m displayed the second. As lemon sharks use waters less than 5 m depth to hunt, perform social behaviours and predator avoidance, results highlight the importance of properly managing these habitats for their conservation, especially in areas where tourism has increased substantially.(AU)

As táticas de caça do tubarão-limão, Negaprion brevirostris, são descritas a partir de observações subaquáticas e de mirantes no Arquipélago de Fernando de Noronha, no Atlântico ocidental equatorial, Brasil. Duas táticas principais foram observadas em águas rasas de praias arenosas e ambientes recifais: (i) “inspeção do substrato” de fendas e cavidades em fundos recifais e rochosos e (ii) “ataques a sardinhas”, que se referem a ataques repentinos a cardumes de peixes (principalmente sardinhas) na zona de arrebentação. A primeira tática esteve restrita a tubarões jovens com até 2 m de comprimento total, enquanto a segunda foi executada por subadultos e adultos com comprimento total acima de 2 m. Como os tubarões-limão utilizam águas com profundidades inferiores a 5 m para caçar, realizar interações sociais e evitar predadores, os resultados realçam a importância de se manejar adequadamente estes hábitats para sua conservação, especialmente em áreas onde o turismo tem aumentado substancialmente.(AU)

Assuntos