Sobreposição de nicho e partilha de recursos entre cinco espécies simpátricas de bufonídeos (Anura, Bufonidae) do nordeste da Argentina

The niche overlap and resource partitioning were analyzed for five sympatric bufonids from Northeastern Argentina: Rhinella schneideri, R. bergi, R. fernandezae, R. granulosa, and Melanophryniscus cupreuscapularis. The primary objectives were to analyze the diet and pattern of coexistence relative to the microhabitats among species. The bufonids, which are primarily terrestrial, exhibited a preference for small, hard prey such as formicids or coleopterans. The smallest species preferably consumed ants, while R. schneideri preferred beetles. Significant differences were detected for the diets of these five species. In addition, significant overlap in the trophic niche was noted for all species except between R. granulosa and R. schneideri. Studying the diet behaviors and trophic parameters of sympatric species provides important data for understanding the community and for the development of conservation guidelines.Analisamos a sobreposição de nicho e a partilha de recursos entre cinco cinco espécies simpátricas de bufonídeos do nordeste da Argentina: Rhinella schneideri, R. bergi, R. fernandezae, R. granulosa e Melanophryniscus cupreuscapularis. O principal objetivo foi analisar a dieta e o padrão de coexistência entre as espécies em relação aos micro-habitats. Os bufonídeos, primariamente terrestres, mostraram preferência por presas duras e de pequeno porte, como formigas e coleópteros. As espécies menores consumiram preferencialmente formigas, enquanto R. schneideri preferiu besouros. Foram detectadas diferenças significativas entre as dietas das cinco espécies. Além disso, houve sobreposição significativa entre os nichos tróficos de todas as espécies, exceto entre R. granulosa e R. schneideri. O estudo do comportamento alimentar e dos parâmetros tróficos de espécies simpátricas fornece dados importantes para a compreensão da estrutura das comunidades e para o delineamento de estratégias de conservação.Fil: Duré Pitteri, Marta Inés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; ArgentinaFil: Kehr, Arturo Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; ArgentinaFil: Schaefer, Eduardo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; Argentin

A revision of the striatella species group of the genus Rhagoletis (Diptera: Tephritidae)

A taxonomic revision of species of the striatella group, including descriptions ofthree new species from Mexico, Nicaragua and Costa Rica is presented. To date we recognize 6 species in this group: Rhagoletis striatella, R. jamaicensis, R. macquartii, R. triangularis n. sp., R. nicaraguensis n. sp., and R. solanophaga n. sp. Information and records about their distribution, known host plants, and morphological relationships among the species are discussed. A key to the species within the group is presented.Se presenta una revision taxonomic a de las especies del grupo striatella, la cual incluye descripciones de tres nuevas especies provenientes de Mexico, Nicaragua y Costa Rica. Ala fecha reconocemos 6 especies en este grupo: Rhagoletis striatella, R. jamaicensis, R. macquartii, R. triangularis n. sp., R. nicaraguensis n. sp., and R. solanophaga n. sp .. Se discute informacion sobre su distribucion, plantas hospederas conocidas, y las relaciones morfologicas entre sus especies. Ademas se presenta una clave para separar todas las especies del grupo

G\"{o}del-type universes in f(R) gravity

The $f(R)$ gravity theories provide an alternative way to explain the current cosmic acceleration without a dark energy matter component. If gravity is governed by a $f(R)$ theory a number of issues should be reexamined in this framework, including the violation of causality problem on nonlocal scale. We examine the question as to whether the $f(R)$ gravity theories permit space-times in which the causality is violated. We show that the field equations of these $f(R)$ gravity theories do not exclude solutions with breakdown of causality for a physically well-motivated perfect-fluid matter content. We demonstrate that every perfect-fluid G\"{o}del-type solution of a generic $f(R)$ gravity satisfying the condition $df/dR > 0$ is necessarily isometric to the G\"odel geometry, and therefore presents violation of causality. This result extends a theorem on G\"{o}del-type models, which has been established in the context of general relativity. We also derive an expression for the critical radius $r_c$ (beyond which the causality is violated) for an arbitrary $f(R)$ theory, making apparent that the violation of causality depends on both the $f(R)$ gravity theory and the matter content. As an illustration, we concretely take a recent $f(R)$ gravity theory that is free from singularities of the Ricci scalar and is cosmologically viable, and show that this theory accommodates noncausal as well as causal G\"odel-type solutions.Comment: 7 pages, V3: Version to appear in Phys. Rev. D (2009), typos corrected, the generality of our main results is emphasized. The illustrative character of a particular theory is also made explici

Spectral averaging techniques for Jacobi matrices

Spectral averaging techniques for one-dimensional discrete Schroedinger operators are revisited and extended. In particular, simultaneous averaging over several parameters is discussed. Special focus is put on proving lower bounds on the density of the averaged spectral measures. These Wegner type estimates are used to analyze stability properties for the spectral types of Jacobi matrices under local perturbations