Sex allocation and sex-dependent selection for body size in Trypoxylon rogenhoferi Kohl (Hymenoptera, Sphecidae)

Two populations of the wasp Trypoxylon rogenhoferi Kohl, 1884 from São Carlos and Luís Antônio, State of São Paulo, Brazil, were observed and sampled from May 1999 to February 2001 using trap-nests. This mass-provisioning wasp was used to test some aspects of optimal sex allocation theory. Both populations fit all the predictions of the models of Green and Brockmann and Grafen. Maternal provisions determined the size of each offspring, and females allocated well-stocked brood cells to daughters, the sex that benefits most being large. This strategy resulted in a difference in size between the sexes. In São Carlos, female weight at emergence was 1.18 times that of males, in Luís Antônio this value was 1.13. The brood cell volume was correlated with both wing length and weight at emergence in both sexes, and the chance that a given brood cell contained a male offspring decreased with increased brood cell volume. In T. rogenhoferi female body size was related to fitness. Larger females were able to collect more mass of spiders per day, the spiders they captured were heavier, and they provisioned more brood cells per day. They also produced larger daughters. For males, no relationship between body size and fitness was found, but the data were scarce. Since the patterns of provisioning were variable among different females in both study sites, it is possible that the females not follow a unique strategy for sex allocation. The sex ratio and/or investment ratio in the São Carlos population was female-biased and in Luís Antônio, male-biased. In spite of the influence of trap-nests diameters on male production in Luís Antônio, there is some evidence that in São Carlos population the local availability of prey and/or lower rate of parasitism may be major forces in determining the observed sex ratio, but further studies are necessary to verify such hypothesis.

Regional allocation of skills

This paper addresses three questions: (1) why does the share of skilledworkers in regional population tend to be higher in wealthier regions? (2)what determines changes in this share over time? and (3) why is it that internalmigration tends to raise average skill levels of the receiving regions relativeto that of the sending regions? I construct a two--region dynamic model withagglomeration and congestion to answer these questions. It is shown that,under certain relationship between wages and demand for land, unskilledworkers are discouraged more strongly from living in a wealthier region andare less mobile than skilled workers.

Dictionnaire général de géographie universelle ancienne et moderne, historique, politique, littéraire et commerciale. accompagné d'une introduction à l'étude de la géographie dans ses rapports avec l'histoire. T. 2 / par Ennery et Hirth ; par Ch. Cuvier,...

Comprend : Introduction à l'étude de la géographie dans ses rapports avec l'histoire...

Dictionnaire général de géographie universelle ancienne et moderne, historique, politique, littéraire et commerciale. accompagné d'une introduction à l'étude de la géographie dans ses rapports avec l'histoire. Tome 3 / par Ennery et Hirth ; par Ch. Cuvier,...

Comprend : Introduction à l'étude de la géographie dans ses rapports avec l'histoire...

Dictionnaire général de géographie universelle ancienne et moderne, historique, politique, littéraire et commerciale. accompagné d'une introduction à l'étude de la géographie dans ses rapports avec l'histoire. T. 1 / par Ennery et Hirth ; par Ch. Cuvier,...

Comprend : Introduction à l'étude de la géographie dans ses rapports avec l'histoire...

Dictionnaire général de géographie universelle ancienne et moderne, historique, politique, littéraire et commerciale. accompagné d'une introduction à l'étude de la géographie dans ses rapports avec l'histoire. T. 4 / par Ennery et Hirth ; par Ch. Cuvier,...

Comprend : Introduction à l'étude de la géographie dans ses rapports avec l'histoire...

On certain greedoid polyhedra, partially indexable scheduling problems and extended restless bandit allocation indices

We present a polyhedral framework for establishing general structural properties on optimal solutions of stochastic scheduling problems, where multiple job classes vie for service resources: the existence of an optimal priority policy in a given family, characterized by a greedoid(whose feasible class subsets may receive higher priority), where optimal priorities are determined by class-ranking indices, under restricted linear performance objectives (partial indexability). This framework extends that of Bertsimas and Niño-Mora (1996), which explained the optimality of priority-index policies under all linear objectives (general indexability). We show that, if performance measures satisfy partial conservation laws (with respect to the greedoid), which extend previous generalized conservation laws, then theproblem admits a strong LP relaxation over a so-called extended greedoid polytope, which has strong structural and algorithmic properties. We present an adaptive-greedy algorithm (which extends Klimov's) taking as input the linear objective coefficients, which (1) determines whether the optimal LP solution is achievable by a policy in the given family; and (2) if so, computes a set of class-ranking indices that characterize optimal priority policies in the family. In the special case of project scheduling, we show that, under additional conditions, the optimal indices can be computed separately for each project (index decomposition). We further apply the framework to the important restless bandit model (two-action Markov decision chains), obtaining new index policies, that extend Whittle's (1988), and simple sufficient conditions for their validity. These results highlight the power of polyhedral methods (the so-called achievable region approach) in dynamic and stochastic optimization.

Population based resource allocation: The use of hybrid risk adjustment

The emphasis on integrated care implies new incentives that promote coordinationbetween levels of care. Considering a population as a whole, the resource allocation systemhas to adapt to this environment. This research is aimed to design a model that allows formorbidity related prospective and concurrent capitation payment. The model can be applied inpublicly funded health systems and managed competition settings.Methods: We analyze the application of hybrid risk adjustment versus either prospective orconcurrent risk adjustment formulae in the context of funding total health expenditures for thepopulation of an integrated healthcare delivery organization in Catalonia during years 2004 and2005.Results: The hybrid model reimburses integrated care organizations avoiding excessive risktransfer and maximizing incentives for efficiency in the provision. At the same time, it eliminatesincentives for risk selection for a specific set of high risk individuals through the use ofconcurrent reimbursement in order to assure a proper classification of patients.Conclusion: Prospective Risk Adjustment is used to transfer the financial risk to the healthprovider and therefore provide incentives for efficiency. Within the context of a National HealthSystem, such transfer of financial risk is illusory, and the government has to cover the deficits.Hybrid risk adjustment is useful to provide the right combination of incentive for efficiency andappropriate level of risk transfer for integrated care organizations.