Morphological patterns and community organization in leaf-litter ant assemblages

We present a new approach to determine the number and composition of guilds, using the hyperdiverse leaf-litter ant fauna as a model, based on appropriate morphological variables and species co-occurrence null models to describe the complex assemblages of interacting Species Community structure at the 1-m(2) scale. We obtained 18 linear morphometric measures from 949 workers of 171 leaf-litter ant species (18762 measurements) surveyed in four Atlantic Forest localities to test whether the assemblages are morphologically structured; the morphological characters were selected to indicate diet and foraging habits. Principal components analysis was used to characterize the morphospace and to describe the guild structure (number of species and composition). The guild proportionality assembly rule (significant tendency toward constant proportion of species in guilds) was assessed at the 1-m(2) scale. Our analysis indicates that the division of leaf-litter ants into guilds is based mainly on microhabitat distribution in the leaf-litter, body size and shape, eye size, and phylogeny. The same guild scheme applied to four more sites shows that different Atlantic Forest areas have the same leaf-fitter ant guilds. The guild proportionality assembly rule was confirmed for most guilds, Suggesting that there are guild-specific limitations on species coexistence within assemblages; on the other hand, in a few cases the variance in guild proportion was greater than expected under the null assumptions. Other studies on ant functional group classification are partially supported by our quantitative morphological analysis. Our results, however, imply that there are more compartments than indicated in previous models, particularly among cryptic species (confined to soil and litter) and tropical climate specialists. We argue that a general null model for the analysis of species association based oil morphology can reveal objectively defined groups and may thus contribute to a robust theory to explain community structure in general and have important consequences on studies of litter ant community ecology in particular.

Allometric growth of two species of Ephemeroptera from Neotropical mountains streams

The present study evaluated the relative growth and allometry of Massartella brieni Lestage and Thraulodes sp. (Leptophlebiidae: Ephemeroptera). The morphometric analysis was based on 23 measurements and was conducted using a multivariate approach. Throughout postembryonic ontogeny, all of the head measurements, including those of the mouthparts, exhibited negative allometric growth. The mesothorax and wing pad exhibited positive allometric growth. The hind legs lengths in M. brieni and the fore and hind legs lengths in Thraulodes sp. exhibited positive allometry. The abdominal length in these two species exhibited positive allometric growth. Positive allometry was also observed along the abdomen width for M. brieni, and isometry was observed for Thraulodes sp. The relative strengthening of the thorax (in preparation for the winged stage) and the relative increase in the abdomen (which may be related to the development of the reproductive structures) during growth indicate that many of the structures that exhibit positive allometric growth are related to the transition from the aquatic to the adult stage of development.

Mid- to late-Holocene paleoceanographic changes on the southeastern Brazilian shelf based on grain size records

; High-resolution grain size analyses of three AMS (14)C-dated cores from the Southeastern Brazilian shelf provide a detailed record of mid- to late-Holocene environmental changes in the Southwestern Atlantic Margin. The cores exhibit millennial variability that we associate with the previously described southward shift of the Inter Tropical Convergence Zone (ITCZ) average latitudinal position over the South American continent during the Holocene climatic maximum. This generated changes in the wind-driven current system of the SW Atlantic margin and modified the grain size characteristics of the sediments deposited there. Centennial variations in the grain size are associated with a previously described late-Holocene enhancement of the El Nino-Southern Oscillation (ENSO) amplitude, which led to stronger NNE trade winds off eastern Brazil, favouring SW transport of sediments from the Paraiba do Sul River. This is recorded in a core from off Cabo Frio as a coarsening trend from 3000 cal. BP onwards. The ENSO enhancement also caused changes in precipitation and wind pattern in southern Brazil, allowing high discharge events and northward extensions of the low-saline water plume from Rio de la Plata. We propose that this resulted in a net increase in northward alongshore transport of fine sediments, seen as a prominent fine-shift at 2000 cal. BP in a core from similar to 24 degrees S on the Brazilian shelf. Wavelet-and spectral analysis of the sortable silt records show a significant similar to 1000-yr periodicity, which we attribute to solar forcing. If correct, this is one of the first indications of solar forcing of this timescale on the Southwestern Atlantic margin.

Grain size effect on the structural and dielectric properties of Pb0.85La0.15TiO3 ferroelectric ceramic compound

This paper presents a study of the influence of particle size on the structural and dielectric properties of Pb0.85La0.15TiO3 (PLT15) ferroelectric ceramic samples. The samples were prepared with average grain size of 1.69 +/- 0.08 mu m and 146 +/- 8 nm using, respectively, conventional and spark plasma sintering techniques. A decrease in the tetragonality degree as the crystallite size decreased was explained by an internal stress caused by the existence of a large amount of grain boundaries. The local structure exhibited no significant modification and the dielectric measurements showed a diffuse phase transition and a reduction in the permittivity magnitude at T-m as the average grain size decreased. The nanostructured ceramic sample prepared at a relatively lower temperature and sintering time presented a dielectric constant value of approximately 2000 at room temperature. (c) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.