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In higher latitudes of the northern hemisphere, anadromous fishes can act as biological vectors, moving marine-derived nutrients into freshwater ecosystems during their reproductive migration. Much less information is available on the potential role of marine and estuarinerelated fishes as biological vectors in subtropical latitudes. Here, we investigated whether mullet juveniles might transport marine nutrients into the freshwater food webs of coastal streams in southern Brazil (32°17'S, 52°15'W). To test this hypothesis, we analyzed the stable isotope ratios of carbon (δ 13 C) and nitrogen (δ 15 N) in 10 basal production sources and 10 consumer species, including juvenile mullets, at 3 sites (surf zone, lower stream reach, headwater reach) along a marine−freshwater gradient. Our results revealed a significant decreasing trend in δ 15 N and δ 13 C values from the sea to the freshwater sites, suggesting an importation and incorporation of marine-derived nutrients into the coastal stream. A mixing model showed a marked shift in assimilation from marine to freshwater production sources by mullet Mugil liza juveniles as they moved from the surf zone into the coastal stream (lower stream and headwater reaches). Our mixing model also indicated that material of marine origin is assimilated by freshwater predators, particularly those found at the lower stream reach. Further experimental and field work is needed to evaluate the implications of marine-derived carbon and nitrogen transport by juvenile mullets for the structure and dynamics of food webs in coastal streams.KEY WORDS: Brazil · Food web spatial subsidies · Freshwater piscivore · Mugil liza · Sea −land connectivity · SIAR mixing models

Predation is the major selective force that drives the development of a series of defense mechanisms by the species. These mechanisms are efficient in that it limits the ability of predators to detect, recognize and subdue their prey. In lizards for example, the tail loss and locomotor escape are the most common defensive behavior reported on the literature. Additionally, in response to external stimuli, some lizards exhibit a peculiar defensive behavior: death-feigning or thanatosis. Here we describe the first record of death-feigning in a population of Liolaemus occipitalis in a coastal sand dune habitat in Southernmost Brazil. A total of 86 individuals were tested. During handling 75.6% of lizards feigned death. The duration of this behavior was longer when the observer remained closer to the lizards, suggesting the ability of L. occipitalis to evaluate the predation risk. Resumo: A pressão exercida pela predação é a principal força seletiva que direciona o estabelecimento de uma série de mecanismos de defesa por parte das espécies. Esses mecanismos são eficientes na medida em que limitam a capacidade dos predadores em detectar, reconhecer ou subjugar suas presas. Em lagartos, por exemplo, os comportamentos defensivos mais frequentemente citados na literatura são a autotomia caudal e a fuga. Além disso, em resposta a estímulos externos, alguns lagartos podem exibir um comportamento peculiar: fingem-se de mortos (tanatose). Neste estudo descrevemos o primeiro registro de tanatose em uma população de Liolaemus occipitalis em área de dunas costeiras no extremo Sul do Brasil. MethodsThe data presented in this study was collected between November 2009 and January 2010 in the municipality of Rio Grande, RS, in an area known as Balneário Cassino, southernmost Brazil (32º 07' 54.65'' -32º 17' 35.07'' S and 52º 06' 38.80'' -52º 20' 53.36'' W) located at sea level. The area consists of well preserved wet habitats formed by meadows with a mosaic of dunes, sand dune vegetation and temporary lagoons. The climate is classified as subtemperate (Maluf 2000), with an average annual maximum temperature of 23.3 °C and average annual minimum temperature of 12.7 ºC. The seasons are well defined, with rainfall homogeneously distributed along the year and averaging 1252 mm between 1931and1990 (INMET 2010). During field surveys of the regional herpetofauna, we captured 86 individuals of Liolaemus occipitalis using pitfall traps with drift fences (Brasileiro et al. 2005). The lizards remained a maximum of eight hours in buckets containing water and shelter to protect them against the sunlight, minimizing the stress on captured animals. All lizards were handled carefully during measurements (body size and mass), sex determination, and assessment of the reproductive condition of females by palpation (Fitch 1987). While being held, some individuals feigned death (Figure 1). The animals that exhibited this behavior were immediately placed on the ground and observed from two distances, 1 and 7 m, whose order was set at random....

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