Pitfall trapping does not reliably index the diet or prey resources of Masked Lapwings

Vertebrate ecologists often assess invertebrate prey resources using techniques which sample invertebrate assemblages, and assume such sampling reflects the diet of their focal species. We compare the invertebrate assemblages as recorded by pitfall traps for Masked Lapwing Vanellus miles breeding territories in Phillip Island, Australia, and show that these differ from assemblages recorded in the stomach contents of local Masked Lapwings. Pitfalls traps did not reveal any difference in assemblages between sites where Masked Lapwings bred, and sites where they did not. Thus, pitfall trapping alone is unlikely to adequately index prey availability for Masked Lapwings.

Preference for feeding at habitat edges declines among juvenile blue crabs as oyster reef patchiness increases and predation risk grows

Both habitat patchiness and behaviorally-mediated indirect effects (BMIEs; predator- induced changes in prey behavior that affect the prey's resources) are important in many food webs, but the relationships between these 2 factors have yet to be investigated. To explore effects of habitat patchiness and variation in perceived risk of predation on food-web dynamics, we conducted a factorial experiment in a model aquatic food chain of predator-prey-resource using 2 contrasting predators (adult blue crab Callinectes sapidus and toad fish Opsanus tau), juvenile blue crab as prey, and mussel Geukensia demissa as resource. Both predator presence and habitat patchiness influenced the prey's preference for consuming resources at patch edges instead of interiors. The preference of prey for consuming resources at habitat edges was 4 times stronger in continuous oyster reef habitat than in smaller habitat patches. This suggests that interior resources in continuous habitat experience a refuge from consumption, but this refuge is largely lost in patchy habitat. The mere presence of predators reduced the prey's preference for consuming resources at habitat edges. This BMIE was significant for the ambush predator (toadfish) and the treatment containing both predators, but not for the actively hunting predator (adult blue crab). We conclude that habitat patchiness and predator presence can jointly affect resource distribution by inducing shifts in prey foraging behavior, revealing a need to incorporate BMIEs into habitat fragmentation studies. This conclusion has broad and growing relevance as anthropogenic factors increasingly modify predator abundances and fragment coastal habitats. © Inter-Research 2012.

How small-scale variation in oyster reef patchiness influences predation on bivalves

As oyster fishing continues to degrade reef habitat along the US Atlantic coast, oyster reefs appear increasingly fragmented on small spatial scales. In outdoor mesocosms, experiments tested how consumption of representatives of 4 different bivalve guilds by each of 3 mesopredators varies between continuous and fine-scale patches of oyster reef habitat. The mesopredator that fed least (stone crab) exhibited no detectable change in consumption on any bivalve (ribbed mussel, bay scallop, hard clam, and 3 size classes of eastern oyster). Consumption of bay scallops by both blue crabs and sheepshead fish was greater in small patches than in continuous oyster reef habitat. Of the bivalve guilds tested, only the scallop possesses swimming motility sufficient to reduce predation, an escape response that would likely leave the bivalve protected within structured habitat in larger continuous oyster reefs. Sheepshead consumed more small oysters in the continuous habitat than in the fine patches, while no other predator-prey interaction exhibited differential feeding as a function of habitat patchiness. Consequently, predation by mesopredators on bivalves can vary with the scale of oyster reef patchiness, but this process may depend upon the bivalve guild. Understanding the role of habitat patchiness on fine scales may be increasingly important in view of the declines in apex predatory sharks leading to mesopredator release, and global climate change directly and indirectly enhancing stone crab abundances, thereby increasing potential predation on bivalves.

The effect of social security, demography and technology on retirement

This article investigates the causes in the reduction of labor force participation of the old. We argue that the changes in social security policy, in technology and in demography may account for most of the changes in retirement over the second part of the last century in the U.S. economy. We develop a dynamic general equilibrium model with endogenous retirement that embeds social security legislation. The model is able to match very closely the increase in the retirement rate of males aged 65 and older. It also quanti es the isolated impact on retirement and on the solvency of the social security system of the di¤erent factors. The model suggests that technological and demographic changes had a strong in uence on retirement, so that it would have increased signi cantly even if the social security rules had not changed. However, as the latter became much more generous in the past, changes in social security policy can account not only for a sizeable part of the expansion of retirement, but also for the most of the observed increase in the social security expenses as a share of GDP.

The effect of social security, demography and technology on retirement

This article investigates the causes in the reduction of labor force participation of the old. We argue that the changes in social security policy, in technology and in demography may account for most of the changes in retirement over the second part of the last century in the U.S. economy. We develop a dynamic general equilibrium model with endogenous retirement that embeds social security legislation. The model is able to match very closely the increase in the retirement rate of males aged 65 and older. It also quanti es the isolated impact on retirement and on the solvency of the social security system of the di¤erent factors. The model suggests that technological and demographic changes had a strong in uence on retirement, so that it would have increased signi cantly even if the social security rules had not changed. However, as the latter became much more generous in the past, changes in social security policy can account not only for a sizeable part of the expansion of retirement, but also for the most of the observed increase in the social security expenses as a share of GDP.

The effect of social security, health, demography and technology on retirement

This article studies the determinants of the labor force participation of the elderly and investigates the factors that may account for the increase in retirement in the second half of the last century. We develop a life-cycle general equilibrium model with endogenous retirement that embeds Social Security legislation and Medicare. Individuals are ex ante heterogeneous with respect to their preferences for leisure and face uncertainty about labor productivity, health status and out-of-pocket medical expenses. The model is calibrated to the U.S. economy in 2000 and is able to reproduce very closely the retirement behavior of the American population. It reproduces the peaks in the distribution of Social Security applications at ages 62 and 65 and the observed facts that low earners and unhealthy individuals retire earlier. It also matches very closely the increase in retirement from 1950 to 2000. Changes in Social Security policy - which became much more generous - and the introduction of Medicare account for most of the expansion of retirement. In contrast, the isolated impact of the increase in longevity was a delaying of retirement.

Essays on health care reform, wealth inequality, and demography

This thesis contains three chapters. The first chapter uses a general equilibrium framework to simulate and compare the long run effects of the Patient Protection and Affordable Care Act (PPACA) and of health care costs reduction policies on macroeconomic variables, government budget, and welfare of individuals. We found that all policies were able to reduce uninsured population, with the PPACA being more effective than cost reductions. The PPACA increased public deficit mainly due to the Medicaid expansion, forcing tax hikes. On the other hand, cost reductions alleviated the fiscal burden of public insurance, reducing public deficit and taxes. Regarding welfare effects, the PPACA as a whole and cost reductions are welfare improving. High welfare gains would be achieved if the U.S. medical costs followed the same trend of OECD countries. Besides, feasible cost reductions are more welfare improving than most of the PPACA components, proving to be a good alternative. The second chapter documents that life cycle general equilibrium models with heterogeneous agents have a very hard time reproducing the American wealth distribution. A common assumption made in this literature is that all young adults enter the economy with no initial assets. In this chapter, we relax this assumption – not supported by the data – and evaluate the ability of an otherwise standard life cycle model to account for the U.S. wealth inequality. The new feature of the model is that agents enter the economy with assets drawn from an initial distribution of assets. We found that heterogeneity with respect to initial wealth is key for this class of models to replicate the data. According to our results, American inequality can be explained almost entirely by the fact that some individuals are lucky enough to be born into wealth, while others are born with few or no assets. The third chapter documents that a common assumption adopted in life cycle general equilibrium models is that the population is stable at steady state, that is, its relative age distribution becomes constant over time. An open question is whether the demographic assumptions commonly adopted in these models in fact imply that the population becomes stable. In this chapter we prove the existence of a stable population in a demographic environment where both the age-specific mortality rates and the population growth rate are constant over time, the setup commonly adopted in life cycle general equilibrium models. Hence, the stability of the population do not need to be taken as assumption in these models.

The Predation of Artemia Nauplii by the Larvae of the Amazon River Prawn, Macrobrachium amazonicum (Heller, 1862), is Affected by Prey Density, Time of Day, and Ontogenetic Development

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Abundance of sedentary consumers and sessile organisms along the wave exposure gradient of subtropical rocky shores of the south-west Atlantic

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Ingestion rates of Artemia nauplii for different larval stages of Macrobrachium rosenbergii

The functional response between ingestion rate and food concentration was determined for each larval stage of Macrobrachium rosenbergii. Artemia franciscana nauplii were supplied at 2,4, 6, 8, 10 and 12 per milliliter. The nauplii were counted by sight using a Pasteur pipette and transferred to Petri dishes containing 40 ml of brackish water (12 parts per thousand) lying on the top of black plastic. One larva at each stage was individually placed into each Petri dish containing different food density. After 24 h, each larva was removed from the Petri dish and the leftover nauplii were counted. The amount consumed was determined by the difference between the initial and final number of nauplii. Ingestion rate (I) increased as food density (P) increased and was defined by the model I=I-m(1-e(-kP)). The results suggest four levels of ingestion during larval development. The first level includes stages II, III and IV, with average maximum consumption of about 40 nauplii/day; the second level includes stages V and VI, with consumption of approximately 55 nauplii/day; the third level includes stages VII and VIII, with consumption of 80-100 nauplii/day. The fourth level includes stages IX, X and XI, in which the high values for maximum ingestion (Im) exceed the load capacity of the medium. The low values for constant k (that may correspond to the adaptability of the food to prey characteristics, such as, size, mobility, etc.) obtained for stages IX, X and XI indicated that Artemia is not an adequate prey and there is necessity of a supplementary diet. The best relationship between predator and prey seemed to occur during stage IV Results obtained in the present work may subsidize future researches and serve as a guideline for practical considerations of feeding rates. (C) 2003 Elsevier B.V. B.V. All rights reserved.

The preimaginal stages of the ensign wasp Evania appendigaster (Hymenoptera, Evaniidae), a cockroach egg predator

Evania appendigaster is a cosmopolitan wasp that deposits eggs in the oothecae of some species of cockroaches; its larvae then consume the cockroach eggs and embryos. It is a candidate for the biological control of cockroaches, but little is known about its basic biology. Here we describe the external morphology of all immature stages of E. appendigaster and compare them with the larvae of related species. The life cycle of E. appendigaster includes three larval instars, each with 13 body segments. Their mouthparts were generally reduced, except for the mandibles, which were always sclerotized and toothed, and were especially robust in second-instar larvae. Antennal and mouthpart sensilla were basiconic and difficult to observe. Larvae of E. appendigaster are similar in form to other described evaniid larvae, but quite different from the two available descriptions of larvae of gasteruptiid and aulacid wasps. Further descriptions of evaniid larvae will be useful in determining how widespread this morphology is within the family, and in understanding phylogenetic relationships within Hymenoptera.

Prey captured and used in Polistes versicolor (Olivier) (Hymenoptera: Vespidae) Nourishment

As vespas sociais são predadoras de muitas espécies de insetos e o estudo de suas presas pode revelar seu potencial para programas de controle biológico de pragas. Foram realizadas 240h de coleta de presas em 32 colônias de Polistes versicolor (Olivier) no município de Juiz de Fora, MG, de março de 2000 a fevereiro de 2001. As presas capturadas por P. versicolor foram, principalmente, das ordens Lepidoptera (95,4%) e Coleoptera (1,1%) além de 3,4% de indivíduos não identificados. A espécie mais coletada foi Chlosyne lacinia saundersii Doubleday & Hewitson (13,5%) (Lepidoptera: Nymphalidae) e o número total estimado de presas capturadas por colônia de P. versicolor foi de 4.015 indivíduos por ano. Isso mostra que a espécie pode ser utilizada em programas de manejo integrado de pragas de insetos herbívoros, principalmente lagartas desfolhadoras.

Respostas funcionais de diferentes tamanhos de Tilápia do Nilo; Oreochromis niloticus; predando zooplâncton

The Nile tilapia, Oreochromis niloticus, is an important omnivorous fish in the reservoirs of the semi-arid region of Brazil. Throughout its growth tilapia s feeding behavior changes from a visual predator of zooplankton to a filter-feeder, collecting suspended particulate matter, including planktonic organisms, through pumping. This feature results in different impacts of tilapia on plankton community as the fish grows. Aiming to quantify the functional response of different sizes of Nile tilapia on zooplankton experiments in microcosms scale in the laboratory and in mesocosm scale in the field were carried out. The data were fitted to four different models of functional response. The best fits were obtained for nonlinear models in laboratory experiments. While the experiments in mesocosms were the best settings for responses of type I (juvenile and adult tilapia) and type III (fry). The Manly's alpha index was used to evaluate the feeding selectivity of tilapia on the three main groups of the zooplankton in the experiments in mesocosms. The results show that: (i) rotifers were the preferred prey of fingerlings,(ii) copepods were rejected by fry and juvenile tilapia and (iii) adult fish fed non-selectively on copepods, cladocerans and rotifers. The functional response models obtained in this research can be applied to population models and help in modeling the dynamics of interactions between Nile tilapia and the planktonic communities in the reservoirs of the semi-arid

Modelo de avaliação de risco : São o crescimento e a estequiometria dos girinos afetados pelo efeito interativo entre a presença do predador e da densidade de coespecíficos?

Many prey organisms change their phenotype to reduce the predation risk. However, such changes are associated with trade-offs, and can have negative effects on prey growth or reproduction. Understand how preys assess the predation risk is essential to evaluate the adaptive value of predator-induced phenotypic and its ecological consequences. In this study, we performed a mesocosm experiment to test: i) if growth and stoichiometry of Lithobates catesbeianus tadpoles is altered in response to giant water bug presence (Belostoma spp.); ii) if these responses depend on tadpoles density in environment. Here, we show that tadpoles growth and stoichiometry are not changed by predator presence, neither in low nor in high densities. Our results suggest that tadpoles exposed to predation risk regulate their physiology to preserve the elemental stoichiometric homeostase of their body and excretion. Further, point out to need for future studies that elucidate under what conditions growth and stoichiometry are changed in response to predation risk

Potencial de alimentação de Chrysoperla externa (Hagen, 1861) (Neuroptera, Chrysopidae) em diferentes densidades de Uroleucon ambrosiae (Thomas, 1878) (Hemiptera, Aphididae)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)