Bias in density estimations using strip transects in dry open-country environments in the Canary Islands

We studied bias in density estimations derived from strip transects in dry open-country in the Canary Islands. We also present some critical remarks on García-del-Rey’s (2005) paper regarding strip transects and the validity of comparisons based on population densities of birds in scrublands on Tenerife island using two different methods: territory mapping and strip transect sampling. Although strip transects with census belts of 25 m do not account for detectability, this method only slightly undervalues true density estimates, and allowed to detect more than 85% of birds present in poorly vegetated environments in the Canary Islands. Previously published works on distribution and abundance of terrestrial birds in the Canary Islands using the strip transect sampling with belts of 25 m on both sides of the observer, thus provide reliable information that only slightly underestimates true densities

Teoría y praxis de modelos generalizados: infiriendo patrones con el paquete estadístico R

Curso de la Sociedad de Amigos del Museo Nacional de Ciencias Naturales - CSICEjemplo de análisis con variables predictoras muy relacionadasEjemplo de análisis con una variable respuesta con elevada carga de cerosEjemplo de análisis con variables predictoras muy relacionadas: -Partial Least Squares (PLS) regression analysis -Similitudes y diferencias con modelos de regresión lineales -Soluciones robustas mediante el uso de bootstrapping -PLS con los paquetes “plsdepot” y “plsRglm”.-- Ejemplo de análisis con una variable respuesta con elevada carga de ceros: -Modelo Generalizado Lineal con una respuesta Binomial Negativa -Modelo Generalizado Lineal “Hurdle” asumiendo inflado de ceros -Modelo Generalizado Lineal Logístico, con una respuesta Binomial estimada como frecuencia -Modelo Generalizado Aditivo con una respuesta Binomial estimada como frecuencia -Revisión de los supuestos canónicos de los modelos -Estimas robustas de los parámetros y significación del modelo -Estimas frecuentistas y multimodelo basadas en la Teoría de la Información -Visualización de los efectos parciales de las predictoras sobre la respuesta -Modelos nulos para estima de significaciónN

Curso práctico de estadística exploratoria. Patrones naturales obtenidos mediante regresión.

Peer Reviewe

Universality in the transport response of molecular wires physisorbed onto graphene electrodes

We analyze the low-voltage transport response of large molecular wires bridging graphene electrodes, where the molecules are physisorbed onto the graphene sheets by planar anchor groups. In our study, the sheets are pulled away to vary the gap length and the relative atomic positions. The molecular wires are also translated in directions parallel and perpendicular to the sheets. We show that the energy position of the Breit-Wigner molecular resonances is universal for a given molecule, in the sense that it is independent of the details of the graphene edges, gaps lengths or of the molecule positions. We discuss the need to converge carefully the k-sampling to provide reasonable values of the conductance.Comment: 6 pages, 6 figure

Impact of edge shape on the functionalities of graphene-based single-molecule electronics devices

We present an ab-initio analysis of the impact of edge shape and graphene-molecule anchor coupling on the electronic and transport functionalities of graphene-based molecular electronics devices. We analyze how Fano-like resonances, spin filtering and negative differential resistance effects may or may not arise by modifying suitably the edge shapes and the terminating groups of simple organic molecules. We show that the spin filtering effect is a consequence of the magnetic behavior of zigzag-terminated edges, which is enhanced by furnishing these with a wedge shape. The negative differential resistance effect is originated by the presence of two degenerate electronic states localized at each of the atoms coupling the molecule to graphene which are strongly affected by a bias voltage. The effect could thus be tailored by a suitable choice of the molecule and contact atoms if edge shape could be controlled with atomic precision.Comment: 11 pages, 20 figure

Variación geográfica de la riqueza de especies invernantes en la península Ibérica. Estacionalidad y determinismo ambiental.

Peer Reviewe

Occurrence data may provide unreliable thermal preferences and breadth of species

Accurate information on the thermal preference and specialization of species is needed to understand and predict species geographical range size and vulnerability to climate change. Here we estimate the position and breadth of species within thermal gradients based on the shape of the response curve of species abundance to temperature. The objective of the study is to compare the measurements of this approach based on abundance data with those of the classical approach using species’ occurrence data. The relationship between species’ relative abundance and minimum winter temperature of 106 bird species wintering in the Iberian Peninsula is modeled at 100 Km2 resolution with quadratic logistic regressions. From these models we calculated the preferred temperature of species as the temperature at which the abundance is maximized, and the thermal breadth of species as the relative area under the temperature-abundance curve. We also estimated the thermal preferences and breadth of species as the average temperature and temperature range of the UTM cells in which the species are present. The abundance-temperature response curves reveal that birds prefer higher temperatures to overwinter, and are more thermally selective, than is measured by the classical approach. Moreover, response curves detect a higher inter-specific variability in both thermal preferences and thermal breadth of species. As occurrence data gives the same weight to cells with one or many individuals, the average temperature of the cells in which the species is present roughly reflects the average temperature in the region of study and not the environmental preferences of species.This paper is a contribution to projects CGL2008-02211/BOS and CGL2011-28177/BOS of the Spanish Ministry of Education and Science.Peer reviewe