Feeding habits of six anuran (Amphibia: Anura) species in a rainforest fragment in Northeastern Brazil

Although Brazil encompasses one of the most abundant anuran faunas in the world, quantitative information on anuran ecology and diet are limited, especially in the Northeastern region. We analyzed the diet of six species: Hyla albomarginata, Hyla cf. branneri, Hyla minuta, Phyllomedusa aff. hypochondrialis (Hylidae), Leptodactylus natalensis, and Physalaemus cuvieri (Leptodactylidae) in a temporary pond in a rainforest remnant in Pernambuco, between 1999-2000. We analyzed diet composition, degree of food preference, and seasonal variations in diet. Leptodactylus natalensis and P. cuvieri showed higher diet diversity, whereas H. minuta consumed fewer food items. Insecta, Arachnida, and plants were preferential items for most species. Acari were consumed by all species; Hymenoptera, Odonata, and Coleoptera were also often consumed. A slight increase in diet diversity occurred in the rainy season. The species showed a generalist feeding behaviour, although P. cuvieri consumed Formicidae as major prey item.

Water depth selection during foraging and efficiency in prey capture by the egrets Casmerodius albus and Egretta thula (Aves, Ardeidae) in an urban lagoon in Rio de Janeiro State, Brazil

This study aimed to evaluate the water depth selection during foraging, the efficiency in prey capture, and the food items captured by Casmerodius albus (Linnaeus, 1758) and Egretta thula (Molina, 1782). The work was conducted at an urban lagoon, Lagoa Rodrigo de Freitas, Rio de Janeiro. Four transects were made each month (two in the morning and two in the afternoon) for six months. When the birds were detected foraging, the water depth and the types of prey captured were recorded. There was no significant relationship between the foraging efficiencies of the two species. However, they differed in relation to the water depth when foraging, and also in the food items captured. Casmerodius albus captured mainly fishes while Egretta thula captured mainly invertebrates. The results suggest that the differences in water depth when foraging and the food items captured allow a differential use of the food resources available by C. albus and E. thula at Lagoa Rodrigo de Freitas.

Prey consumed by Guiana dolphin Sotalia guianensis (Cetacea, Delphinidae) and franciscana dolphin Pontoporia blainvillei (Cetacea, Pontoporiidae) in an estuarine environment in southern Brazil

The present study provides information about the diet of sympatric populations of small cetaceans in the Babitonga Bay estuary. This is the first study on the diet of these species in direct sympatry. The stomach contents of seven Guiana dolphins Sotalia guianensis and eight franciscanas Pontoporia blainvillei were analyzed. The prey of both cetaceans was mostly teleost fishes, followed by cephalopods. We identified 13 teleost fishes as part of the diet of the franciscanas, and 20 as part of the diet of Guiana dolphins. Lolliguncula brevis was the only cephalopod recorded, and was the most important prey for both cetaceans. Stellifer rastrifer and Gobionellus oceanicus were also important for franciscana, so as Mugil curema and Micropogonias furnieri were important for Guiana dolphins. Stellifer rastrifer and Cetengraulis edentulus were the fishes with the highest frequency of occurrence for franciscana (50%), while Achirus lineatus, C. edentulus, S. brasiliensis, Cynoscion leiarchus, M. furnieri, M. curema, Diapterus rhombeus, Eugerres brasilianus and G. oceanicus showed 28.6% of frequency of occurrence for Guiana dolphins. Franciscanas captured greater cephalopods than the Guiana dolphins in both total length (z= -3.38; n= 40; p< 0.05) and biomass (z = -2.46; n = 40; p<0.05). All of the prey species identified occur inside the estuary, which represents a safe habitat against predators and food availability, reinforcing the importance of the Babitonga Bay for these cetacean populations.

Diversity and habitat preference of medium and large-sized mammals in an urban forest fragment of southwestern Amazon

We assessed the species composition and abundance of medium and large-sized mammals in an urban forest fragment in the Brazilian Amazon, and recorded the preference of some species for particular phytophysiognomies. We placed nine transects with 20 sand plots each in three phytophysiognomies: open rainforest with a dominance of bamboos (OFB), open rainforest with palm trees (OFP), and dense rainforest (DF). We calculated species abundance as the number of records/plot.day, in a total of 2,700 plots.day. We recorded twelve mammal species; Sylvilagus brasiliensis (Linnaeus, 1758) and Dasyprocta fuliginosa (Wagler, 1831) were the most abundant. The results differed among phytophysiognomies: DF presented the highest mammal diversity, whereas the species composition of OFP was less similar than that of other phytophysiognomies. Rodents showed higher preference for OFP and Sylvilagus brasiliensis was more abundant in OFB. The study area showed high species richness, with the occurrence of mesopredators, but there was a predominance of common species adaptable to disturbed environments, which reflects the severe isolation degree of the forest fragment and the hunting pressure that is still present.

Cephalopoda as prey of juvenile Southern elephant seals at Isla 25 de Mayo/King George, South Shetland Islands

The aim of the present study was to enhance the knowledge of the feeding habits of the juvenile component of the population of Southern elephant seals [Mirounga leonina (Linnaeus, 1758)] from Isla 25 de Mayo, South Shetland Islands, age class whose diet information is scarce. A total of 60 individuals were stomach lavaged in the spring - summer seasons of three consecutive years (2003, 2004 and 2005) of which 53.3 % (n = 32) presented food remnants. The Antarctic glacial squid Psychroteuthis glacialis Thiele, 1921 was the dominant prey taxon in terms of frequency of occurrence (68.7%), numerical abundance (60.1%) and biomass (51.5%), contributing 84.1% to the total relative importance index. Other squid prey species of importance were Slosarczykovia circumantartica Lipinski, 2001 in terms of occurrence (37.5%) and numerical abundance (14%) and Moroteuthis knipovitchi Filippova, 1972 in terms of biomass (16%). All identified cephalopod prey taxa are distributed south of the Antarctic Polar Front, except for the squid Martialia hyadesi Rochebrune & Mabille, 1889 which has a circumpolar distribution associated to the Polar Frontal Zone. No significant differences in the sizes of P. glacialis preyed upon by elephant seals were found between sexes and years. However, significant interannual differences were found in the taxonomical composition of their diet. This would be associated with temporal changes in food availability at the foraging areas of seals, which in turn may have been influenced by changes in oceanographic conditions as a result of the El Niño Southern Oscillation (ENSO) phenomenon that occurred during part of the study period. Furthermore, a differential response of males and females to this temporal variation was observed, with the former being also associated to a predation on octopods. This would suggest a sexual segregation in foraging habits of this species from the early stages of its life cycle.

Diel vertical migration of predators (planktivorous fish larvae) and prey (zooplankton) in a tropical lagoon

ABSTRACT Based on the hypothesis that diel vertical migration (DVM) is a mechanism of predator avoidance, the objective of the present study was to test for the occurrence of DVM in planktivorous fish larvae of Hypophthalmus edentatus (Spix, 1829) (Siluriformes, Pimelodidae) and Plagioscion squamosissimus (Heckel, 1840) (Perciformes, Sciaenidae), and zooplankton (rotifers, cladocerans and copepods) in an isolated tropical lagoon in the floodplain of the Upper Paraná River, Brazil (region of Parque Nacional de Ilha Grande). We investigated spatial overlap between predators (planktivorous fish larvae) and prey (zooplankton), and tested which physical and chemical variables of the water are related to the DVM of the studied communities. We performed nocturnal (8:00 pm and 4:00 am) and diurnal sampling (8:00 am and 4:00 pm) in the limnetic region of the lagoon for six consecutive months, from October 2010 to March 2011, which comprises the reproductive period of the fish species analyzed. During the day the larvae tried to remain aggregated in the bottom of the lagoon, whereas at night they tried to disperse in the water column. Especially for cladocerans, the diel vertical migration is an important behavior to avoid predation larvae of H. edentatus and P. squamosissimus once decreased spatial overlap between secured and its potential predators, which corroborates the hypothesis that DVM is a mechanism of predator avoidance. Although significant correlations were observed between the abiotic factors and WMD of microcrustaceans at certain times of day, the effect of predation of fish larvae on zooplankton showed more important in this environment, because the small depth and isolation not allow great variation of abiotic factors seasonally and between strata the lagoon.

Revealed cardinal preference

I prove that as long as we allow the marginal utility for money (lambda) to vary between purchases (similarly to the budget) then the quasi-linear and the ordinal budget-constrained models rationalize the same data. However, we know that lambda is approximately constant. I provide a simple constructive proof for the necessary and sufficient condition for the constant lambda rationalization, which I argue should replace the Generalized Axiom of Revealed Preference in empirical studies of consumer behavior. 'Go Cardinals!' It is the minimal requirement of any scientifi c theory that it is consistent with the data it is trying to explain. In the case of (Hicksian) consumer theory it was revealed preference -introduced by Samuelson (1938,1948) - that provided an empirical test to satisfy this need. At that time most of economic reasoning was done in terms of a competitive general equilibrium, a concept abstract enough so that it can be built on the ordinal preferences over baskets of goods - even if the extremely specialized ones of Arrow and Debreu. However, starting in the sixties, economics has moved beyond the 'invisible hand' explanation of how -even competitive- markets operate. A seemingly unavoidable step of this 'revolution' was that ever since, most economic research has been carried out in a partial equilibrium context. Now, the partial equilibrium approach does not mean that the rest of the markets are ignored, rather that they are held constant. In other words, there is a special commodity -call it money - that reflects the trade-offs of moving purchasing power across markets. As a result, the basic building block of consumer behavior in partial equilibrium is no longer the consumer's preferences over goods, rather her valuation of them, in terms of money. This new paradigm necessitates a new theory of revealed preference.

The Effects of Experience on Preference Uncertainty: Theory and Empirics for Public and Quasi-Public Environmental Goods

This paper develop and estimates a model of demand estimation for environmental public goods which allows for consumers to learn about their preferences through consumption experiences. We develop a theoretical model of Bayesian updating, perform comparative statics over the model, and show how the theoretical model can be consistently incorporated into a reduced form econometric model. We then estimate the model using data collected for two environmental goods. We find that the predictions of the theoretical exercise that additional experience makes consumers more certain over their preferences in both mean and variance are supported in each case.

Predator-prey chemical warfare determines the expression of biocontrol genes by rhizosphere-associated Pseudomonas fluorescens.

Soil bacteria are heavily consumed by protozoan predators, and many bacteria have evolved defense strategies such as the production of toxic exometabolites. However, the production of toxins is energetically costly and therefore is likely to be adjusted according to the predation risk to balance the costs and benefits of predator defense. We investigated the response of the biocontrol bacterium Pseudomonas fluorescens CHA0 to a common predator, the free-living amoeba Acanthamoeba castellanii. We monitored the effect of the exposure to predator cues or direct contact with the predators on the expression of the phlA, prnA, hcnA, and pltA genes, which are involved in the synthesis of the toxins, 2,4-diacetylphloroglucinol (DAPG), pyrrolnitrin, hydrogen cyanide, and pyoluteorin, respectively. Predator chemical cues led to 2.2-, 2.0-, and 1.2-fold increases in prnA, phlA, and hcnA expression, respectively, and to a 25% increase in bacterial toxicity. The upregulation of the tested genes was related to the antiprotozoan toxicity of the corresponding toxins. Pyrrolnitrin and DAPG had the highest toxicity, suggesting that bacteria secrete a predator-specific toxin cocktail. The response of the bacteria was elicited by supernatants of amoeba cultures, indicating that water-soluble chemical compounds were responsible for induction of the bacterial defense response. In contrast, direct contact of bacteria with living amoebae reduced the expression of the four bacterial toxin genes by up to 50%, suggesting that protozoa can repress bacterial toxicity. The results indicate that predator-prey interactions are a determinant of toxin production by rhizosphere P. fluorescens and may have an impact on its biocontrol potential.

Factors influencing predation of the Waterbugs Sphaerodema annulatum (Fab.) and S. rusticum (Fab.) on the Disease Transmitting Snail Lymnaea (Radix) luteola (Lamarck)

Variations in the rate of predation of the waterbugs Sphaerodema annulatum and S. rusticum on the snails Lymnaea (Radix) luteola have been noted in respect to the morphs of the waterbugs, size of the prey individuals, densities of prey and predators, temperature and surface area of the waterbody concerned and the seasons. Consumption rate was highest (7.2 and 2.2 individuals per day per individual of S. annulatum and S. rusticum, respectively) in prereproductive ages of the waterbugs. This was followed by a gradual decline with the increase in age of the predators. The consumption rate was gradually higher with the increase of temperature from 20 °C to 35 °C. The bugs failed to survive beyond 35 days at 35 °C. Though the bugs prey upon the snails of all sizes preference for 6.5 ÷ 4.5 mm to 8 ÷ 5 mm individuals by S. annulatum and for 5 ÷ 3 mm to 6.5 ÷ 4.5 mm individuals belonged to 3 ÷ 2 - 4 ÷ 3 mm size group maximum when supplied separately. The rate of predation gradually declined with the rise of predator's desity irrespective of waterbug species. Predation rate increased with increasing prey density. This was level off when the prey snails were 1100 and 700 in number for S. annulatum and S. rusticum respectively. An adult S. annulatum and S. rusticum consumed 5.04, 3.7, 1.43 and 3.36, 2.49, 1.04 snails per day respectively in summer, monsoon and winter.

Preference intensities and risk aversion in school choice: a laboratory experiment

We experimentally investigate in the laboratory two prominent mechanisms that are employed in school choice programs to assign students to public schools. We study how individual behavior is influenced by preference intensities and risk aversion. Our main results show that (a) the Gale-Shapley mechanism is more robust to changes in cardinal preferences than the Boston mechanism independently of whether individuals can submit a complete or only a restricted ranking of the schools and (b) subjects with a higher degree of risk aversion are more likely to play "safer" strategies under the Gale-Shapley but not under the Boston mechanism. Both results have important implications for the efficiency and the stability of the mechanisms.

Habitat, breeding performance, diet and individual age in Swiss barn owls (Tyto alba)

Intensification of farming over the past 50 years has homogenised the landscape structure and contributed to the decline of bird populations in Europe. To better target the conservation of the Barn Owl Tyto alba, we assessed the influence of the landscape structure on breeding performance in western Switzerland. The analyses considered a 23-year data set of breeding parameters collected in an area dominated by intensive agriculture. Using a Geographic Information System approach, landscape characteristics were described around 194 nest sites. Our analyses showed that nest-box occupancy, laying date, clutch and brood size, egg volume and probability of producing a second annual clutch were not significantly associated with any of the eight principal landscape variables (agricultural land, woodland, urban area, hedgerows, cereals, sugar beet, maize and meadow). Nevertheless, the probability that a breeding pair occupied a nest-box decreased the more roads there were surrounding the nest-box. The absence of strong associations between habitat features and breeding parameters suggests that prey availability may be relatively similar between the different breeding sites. In our study area Barn Owls can always find suitable foraging habitats around most nest-boxes.