The mere presence of predators (i.e., predation risk) can alter consumer physiology by restricting food intake and inducing stress, which can ultimately affect prey‐mediated ecosystem processes such as nutrient cycling. However, many environmental factors, including conspecific density, can mediate the perception of risk by prey. Prey conspecific density has been defined as a fundamental feature that modulates perceived risk. In this study, we tested the effects of predation risk on prey nutrient stoichiometry (body and excretion). Using a constant predation risk, we also tested the effects of varying conspecific densities on prey responses to predation risk. To answer these questions, we conducted a mesocosm experiment using caged predators (Belostoma sp.), and small bullfrog tadpoles (Lithobates catesbeianus) as prey. We found that L. catesbeianus tadpoles adjust their body nutrient stoichiometry in response to predation risk, which is affected by conspecific density. We also found that the prey exhibited strong morphological responses to predation risk (i.e., an increase in tail muscle mass), which were positively correlated to body nitrogen content. Thus, we pose the notion that in risky situations, adaptive phenotypic responses rather than behavioral ones might partially explain why prey might have a higher nitrogen content under predation risk. In addition, the interactive roles of conspecific density and predation risk, which might result in reduced perceived risk and physiological restrictions in prey, also affected how prey stoichiometry responded to the fear of predation.

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This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0), which permits reproduction, adaptation, and distribution provided the original author and source are credited. AbstractThere have been few studies about the pollinators of bromeliads of the genus Encholirium. Considering this lack of information, this study comes to fill a gap in the literature on the floral visitors and potential pollinators of E. spectabile. In order to perform this study, we observed the inflorescence of this species between 2011 and 2014 (four years of observation), in the semiarid region of Santa Maria municipality (Rio Grande do Norte state, northeastern Brazil). Floral visitors were observed through focal method. The observations were made during the day, starting at 06h a.m. until 06h p.m., and at night from 07h until 11h59 p.m. In about 1,800 hours of observations, 24 species were recorded visiting E. spectabile flowers, including 4 species of moths (Lepidoptera: Sphingidae and Geometridae), 3 species of bees (Hymenoptera: Apidae), 4 species of hummingbirds (Aves: Trochilidae) and 2 species of bats (Chiroptera: Phyllostomidae), among others. Based on these results, we propose that the macambira bromeliads (E. spectabile) should be considered as key elements in the conservation of various taxonomic groups in the semiarid region, through the umbrella species theory as already proposed for other species of Bromeliaceae. Keywords: associated fauna, caatinga biome, macambiras, Encholirium spectabile, biodiversity. ResumoExistem poucos estudos a respeito dos polinizadores de bromélias do gênero Encholirium. Dessa forma, este estudo vem preencher a lacuna na literatura sobre os visitantes florais e potenciais polinizadores de E. spectabile. Para sua realização, observamos a inflorescência dessa espécie no período de 2011 a 2014 (quatro anos de observações), na região semiárida, no município de Santa Maria, Rio Grande do Norte, Brasil. Os visitantes florais foram registrados por meio do método focal. As observações foram conduzidas durante o dia, começando às 06h da manhã e seguindo até às 18h e, à noite, das 19h às 23h59min. Em cerca de 1.800 horas de observação, 24 espécies foram registradas visitando a inflorescência de E. spectabile, incluindo 4 espécies de mariposas (Lepidoptera: Sphingidae e Geometridae), 3 espécies de abelhas (Hymenoptera: Apidae), 4 espécies de beija-flores (Aves: Trochilidae) e 2 espécies de morcegos (Chiroptera: Phyllostomidae), entre outros. Com base nesses resultados, e subsidiados pela teoria das espécies guarda-chuva, sugerimos que as bromélias macambiras (E. spectabile) sejam consideradas como elementos chave na conservação de vários grupos taxonômicos de região semiárida.Palavras-chave: fauna associada, bioma caatinga, macambiras, Encholirium spectabile, biodiversidade.

Bromeliads are important habitats for reptiles and amphibians, and are constantly used as shelter, refuge, foraging or thermoregulation sites due to their foliar architecture, which allows for constant maintenance of humidity and temperature. This study aimed to identify the herpetofauna inhabiting the non-phytotelmata rupicolous bromeliad Encholirium spectabile Mart. ex Schult. & Schult.f. and to analyze the microhabitat usage of these bromeliads by different species in the Caatinga of northeastern Brazil. From January 2011 to August 2012, we collected data by active search throughout three paralel transects in a rock outcrop in the municipality of Santa Maria, state of Rio Grande do Norte. We recorded four species of anuran amphibians, six lizards, and seven snakes in the bromeliads. The average air temperature was lower and air humidity higher inside than outside the bromeliads, and bromeliads at the rock outcrop borders had lower temperatures and higher humidity than those at the center. We found a significant difference in the distribution of individuals throughout the rock outcrop, with most specimens found at the borders. We also found significant differences regarding the use of each microhabitat by the taxonomic groups, with lizards and snakes using green leaves and dry leaves evenly, along with fewer records in inflorescence stems, and anurans mainly using green leaves, with few records on dry leaves, and no records in the inflorescence stems. This study highlights rupicolous bromeliads as key elements in the conservation and maintenance of amphibians and reptiles in the rock outcrops of Brazilian semi-arid Caatinga.

Abstract. The risk-assessment hypothesis (R-AH) states that prey must consider conspecific density and not simply the concentration of predation cues to evaluate actual predation risk. However, little is known about whether the R-AH might serve to predict predator-inducible plastic responses involving different prey phenotypes. We approached this question through an experiment in outdoor mesocosms, manipulating predation risk (with caged predators) and prey conspecific density to test the importance of R-AH for the expression of predator-induced morphological and behavioral phenotypes. We found behavioral (swimming activity) and morphological (tail width and tail muscle depth) responses of bullfrog tadpoles (Lithobates catesbeianus) to be affected by chemical predation cues. However, only the morphological phenotype responded to the predation-risk:conspecific-density interaction. The width of the tail and the muscle depth of tadpoles were significantly greater when individuals were exposed to predators. However, this effect was not significant in treatments with high prey density in an experimental setup that minimized intraspecific competition. We interpret the differences found among the responses of the phenotypes in terms of the effects of three factors: the potential costs related to each phenotype expression, how these phenotypes are affected by environmental conditions and the immediate response of the phenotypes to actual and perceived prey risk. Our results shed light on the fact that prey individuals use information about population density to estimate actual predation risk from chemical cues. However, different traits are differentially affected, suggesting that trade-off mechanisms associated with the costs of the expression in terms of anti-predator defenses may interfere with the predictions of R-AH for multiple prey phenotypes.

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Habitat use, daily activity periods, and thermal ecology of Ameiva ameiva (Squamata: Teiidae) in a caatinga area of northeastern Brazil. We studied the use of spatial, temporal, and thermal resources by the Neotropical lizard Ameiva ameiva during rainy and dry seasons in a caatinga (xerophilous open forests) environment in northeastern Brazil. Lizards used the vegetation habitats and microhabitats in the ground, but never were seen in the rocky habitat. Adults usually used the arboreal-shrubby habitat, whereas juveniles were sighted more often in the shrubby-herbaceous habitat. Ontogenetic differences in spatial use seem to be linked to different thermal needs between age groups owing to differences in body size. Body temperatures were significantly higher in juveniles than in adults. Most teiid species have elevated body temperatures, usually above 37 o C, and are active during the hottest times of day, as was observed for A. ameiva in this study. Seasonality influenced habitat use and daily activity periods of adults, but not body temperatures. We verified annual fluctuations in adult abundance, with a decline of active lizards in the dry season; this phenomenon may be related to aestivation and/or increased mortality rate during the driest months.Keywords: abundance, body size, ontogeny, seasonality, thermoregulation.Resumo Uso do hábitat, períodos diários de atividade e ecologia térmica de Ameiva ameiva (Squamata: Teiidae) em uma área de caatinga do nordeste do Brasil. Estudamos o uso dos recursos espaciais, temporais e térmicos pelo lagarto neotropical Ameiva ameiva durante as estações seca e chuvosa em um ambiente de caatinga do nordeste do Brasil. Os lagartos utilizaram os hábitats e micro-hábitats de vegetação baixa, mas nunca foram observados no hábitat rochoso. Os adultos 166Phyllomedusa -10(2), December 2011 utilizaram usualmente o hábitat arbóreo-arbustivo, enquanto os juvenis foram observados mais frequentemente no hábitat arbustivo-herbáceo. Diferenças ontogenéticas no uso do espaço parecem estar relacionadas a diferentes necessidades térmicas entre as classes de idade devido a diferenças de tamanho corporal. As temperaturas corporais dos juvenis foram significativamente maiores que as dos adultos. A maioria das espécies de Teiidae possui temperaturas corporais elevadas, usualmente acima de 37 o C, e atividade concentrada nas horas mais quentes do dia, como observado em A. ameiva neste estudo. A sazonalidade influenciou o uso do hábitat e os períodos diários de atividade dos adultos, mas não influenciou as temperaturas corporais. Verificamos flutuações anuais na abundância de indivíduos adultos, com um declínio de lagartos ativos na estação seca; esse fenômeno pode estar relacionado à estivação e/ou ao aumento da taxa de mortalidade durante os meses mais secos.