Las interacciones planta-planta y planta-animal en el contexto de la sucesión ecológica

24 páginas, 2 cuadros, 6 figuras, 103 referencias. La publicación está en la Sección C: Interacciones, capítulo 13 de la 2ª edición. Colección Naturaleza y Parques Nacionales. Serie técnica. Existe una 1ª edición de 2004. Estas investigaciones no se hubieran podido llevar a cabo sin los permisos y facilidades para investigar en los espacios protegidos Parque Nacional de Sierra Nevada y Parque Natural de la Sierra de Baza, proporcionados por la Consejería de Medio Ambiente de la Junta de Andalucía.[EN]: Plant-plant and plant-animal interactions in the context of ecological succession. In Mediterranean environments, the regeneration of a great number of woody species, both tree and shrub, present a spatial pattern associated with established plants, suggesting a net positive balance in plant-plant interactions. In this chapter, from the perspective of successional process, we analyse the mechanisms and ecological consequences of the interactions between pioneer shrubs and tree seedlings, and between these and ungulate herbivores that consume these plants. Under stress situations, the environmental alteration caused by a neighbouring plant (in terms of microclimate, soil, protection from herbivores) can offer a benefit that exceeds the costs that any spatial proximity implies, favouring the development of facilitation between the pioneer shrubs and the seedlings of slow-growing woody species. The positive effect of shrubs on the regeneration of woody species need not to be restricted to only one demographic phase, nor to be generated by only one mechanism, but rather it may be manifested in several stages of recruitment. The spatial association with thorny or unpalatable plants enables more palatable woody species to establish themselves even in habitats where there is high and chronic herbivore pressure. Given that the Mediterranean woodlands can hardly regenerate in open areas for lack of water and/or excessive herbivory, either under the canopy of established trees for lack of light and/or excessive herbivory (or seed predation), the main regeneration niche for many tree species under a wide range of ecological conditions are pioneer plants, capable of colonizing precisely the sites with these conditions of stress and herbivory. A good shrub cover, both of pioneer species and of the intermediate stages of succession, is the best insurance to avoid soil erosion, to achieve natural regeneration of woodlands, and to boost the success of reforestation, since these species encourage progression towards more mature communities.[ES]: Las interacciones planta-planta y planta animal en el contexto de la sucesión ecológica. En ambientes mediterráneos, la regeneración de gran número de especies leñosas arbóreas y arbustivas presenta un patrón espacial asociado a plantas ya establecidas, lo que sugiere la existencia de un balance neto positivo de las interacciones planta- planta. En este capítulo analizamos los mecanismos y consecuencias ecológicas de las interacciones entre arbustos pioneros y plántulas de árboles, y entre éstas y los herbívoros ungulados que las consumen desde una perspectiva de proceso sucesional. En ambientes como los mediterráneos, donde las plantas suelen padecer situaciones de estrés, la modificación ambiental producida por una planta vecina (microclima, suelo, protección frente a herbívoros) puede ofrecer un beneficio que supere los costos que toda proximidad espacial conlleva, lo que favorece el desarrollo de interacciones de facilitación entre los arbustos pioneros y las plántulas de especies leñosas de crecimiento lento. El efecto positivo de los arbustos sobre la regeneración de especies leñosas no tiene por qué estar restringido a una sola fase demográfica, ni ser generado por un solo mecanismo, sino que puede manifestarse en varios estadíos del reclutamiento. La asociación espacial con plantas espinosas o poco palatables permite a las especies leñosas más palatables establecerse incluso en hábitats donde existe una presión de herbivoría elevada y crónica. Ya que el bosque mediterráneo apenas puede regenerarse en áreas abiertas por falta de agua y/o por exceso de herbivoría, ni bajo la copa de los árboles ya establecidos por falta de luz y/o exceso de depredadores de semillas o herbivoría, el nicho de regeneración principal para muchas especies arbóreas en una amplia gama de condiciones ecológicas es bajo las plantas pioneras, capaces de colonizar precisamente lugares con esas condiciones de estrés y herbivoría. Una buena cobertura de matorral, tanto de especies pioneras como de etapas intermedias de la sucesión, es el mejor seguro para evitar la erosión del suelo, conseguir la regeneración natural de los bosques, y mejorar el éxito de las reforestaciones, ya que dichas especies favorecen la progresión hacia comunidades más maduras.Las investigaciones expuestas en este capítulo han sido financiadas a través de los proyectos: FEDER 1FD97-0743-CO3-02, REN2001-4552-E y HETEROMED (REN 2002 4041/GLO y DINAMED CGL 2005-05830-CO3-03/BOS) del MCYT a R.Z y LGA, y a través de los proyectos GV94-2311 y FEDER 1FD97-0551 y AGL2001-1061 a PG-F. Las investigaciones expuestas en este capítulo han sido financiadas a través de los proyectos: FEDER 1FD97-0743-CO3-02, REN2001-4552-E y HETEROMED (REN 2002 4041/GLO y DINAMED CGL 2005-05830-CO3-03/BOS) del MCYT a R.Z y LGA, y a través de los proyectos GV94-2311 y FEDER 1FD97-0551 y AGL2001-1061 a PG-F.Peer reviewe

On the invariant causal characterization of singularities in spherically symmetric spacetimes

The causal character of singularities is often studied in relation to the existence of naked singularities and the subsequent possible violation of the cosmic censorship conjecture. Generally one constructs a model in the framework of General Relativity described in some specific coordinates and finds an ad hoc procedure to analyze the character of the singularity. In this article we show that the causal character of the zero-areal-radius (R=0) singularity in spherically symmetric models is related with some specific invariants. In this way, if some assumptions are satisfied, one can ascertain the causal character of the singularity algorithmically through the computation of these invariants and, therefore, independently of the coordinates used in the model.Comment: A misprint corrected in Theor. 4.1 /Cor. 4.

Seed germination and seedling allogamy in Rosmarinus officinalis: the costs of inbreeding

1) Self-pollination by geitonogamy is likely in self-compatible plants that simultaneously expose large numbers of flowers to pollinators. However, the progeny of these plants is often highly allogamous. Although mechanisms to increase cross-pollination have been identified and studied, their relative importance has rarely been addressed simultaneously in plant populations. (2) We used Rosmarinus officinalis to explore the factors that influence the probability of self-fertilization due to geitonogamy or that purge its consequences, focusing on their effect on seed germination and allogamy rate. For doing this, we experimentally tested the effects of geitonogamy on the proportion of filled seeds and how it influences germination rates. Then during two field seasons, we studied how life-history and flowering traits of individuals influence seed germination and allogamy rates of their progeny in wild populations at the extremes of the altitudinal range. The traits considered were plant size, population density, duration of the flowering season, number of open flowers, flowering synchrony among individuals within populations, and the proportion of male-sterile flowers. (3) We found that most seeds obtained experimentally from self-pollinations were apparently healthy but in fact empty, and that the presence of filled seeds drove the differences in germination rates between self- and cross-pollination experiments. Plants from wild populations consistently showed low germination rates and high rates of allogamy as determined with microsatellites. Germination rates related positively to the length of the flowering season, flowering synchrony and the rate of male-sterile flowers whereas the rate of allogamous seedlings was positively related only to the rate of male-sterile flowers. (4) Rosemary plants purge most of the inbreeding caused by its pollination system by aborting seeds. This study showed that the rates of seed germination and of the resulting allogamy are a function of a complex combination of factors that vary in space and time. Male sterility of flowers, length of the flowering season and flowering synchrony of individuals within populations all favor high rates of cross-pollination, therefore increasing germination and allogamy rates. These flowering traits appear to be highly plastic and respond to local and seasonal environmental conditions

Tourism and fashion: factors affecting trip length

Tourism and shopping are closely related, and the influence of fashion shopping on a tourist's decision to travel is especially significant. The concept of cognitive and hedonic involvement enables us to relate the importance given to shopping by consumers of fashion products and of tourism services. This research analyses whether tourist involvement in fashion shopping has an impact on the length of their stay in a destination. In addition, it examines whether trip length is conditioned by traditional factors, such as demographic indicators (age, gender and income bracket), as well as by cognitive and affective involvement, and shopping motivations (service quality, product quality and shopping enjoyment). The empirical research carried out on a sample of 370 tourists has enabled us to draw interesting conclusions for destination managers and other tourism decision-makers, showing that involvement in fashion, shopping enjoyment, service quality, cognitive involvement in the choice of destination, age, and income significantly predict trip length

Demographic limitation processes

20 páginas, 2 figuras, 1 tabla, 3 cuadros.-- Editor: Valladares, F.[ES]: Procesos de limitación demográfica. Este capítulo ofrece una revisión de los factores que afectan a la regeneración natural de la vegetación, considerando la serie de etapas demográficas que determinan la dinámica demográfica de una pobla- ción. Son muy escasos los estudios disponibles que analizan toda la serie de eventos concatenados entre la producción de flores y frutos y el establecimiento exitoso de una planta adulta reproductiva. También son escasos los trabajos que permiten establecer los efectos aplazados que tienen las interacciones con animales a lo largo del ciclo de regeneración. La aproximación que proponemos cuantifica las pérdidas de propágulos en cada etapa demográfica e identifica “cuellos de botella” del reclutamiento que pue- den colapsar la regeneración natural de una especie. Revisamos una serie de casos de estudio que ilustran diversos procesos de limitación demográfica. El uso de técnicas explícitamente demográficas es fundamental para comprender la evolución de las especies forestales Mediterráneas y para diseñar actuaciones de preservación de sus poblaciones y de su extraordinaria diversidad.[EN]: We review the main factors influencing recruitment limitation in Mediterranean woody species by considering the sequential stages that determine the demographic cycle. Very few studies examine the whole set of demographic stages, from flower production to the successful establishment of adult reproductive plants, and their influence on recruitment. There are also few studies exploring the delayed effects of animal interactions throughout the regeneration cycle, but the information on stage-specific effects is more detailed. We propose an approach that quantifies the propagule losses at each sequential demographic stage and identifies demographic bottlenecks that might collapse population growth. We review a series of case studies illustrating different limitation processes. The use of explicit demographic techniques is central to understand the evolution of Mediterranean woody species and to design sound, ecologically-based, conservation plans to preserve their extraordinary diversity.Juan Arroyo agradece la financiación otorgada a los proyectos 4474-91 (National Geographic Society), PB 91-0894, PB95-0551, 1FD97-0743-CO3-03, PB98-1144, BOS200307924-CO2-01 (MECD, MCyT). Los trabajos de Pedro Jordano han sido financiados con proyectos MECD y MCyT (1FD97-0743-CO3-01, PB 96-0857, BOS2000-1366-C02-01 y REN2003-00273), así como la Junta de Andalucía (PAI). Juan Luis García-Castaño estuvo financiado durante su período pre-doctoral con una beca FPU, AP96-27318040. El trabajo de Fernando Pulido ha sido parcialmente financiado por una beca FPI de la Junta de Extremadura y los proyectos regional IPR-0A050 y estatal BOS2002- 12222-E del Ministerio de Ciencia y Tecnología. Los trabajos de Patricio García-Fayos han sido financiados con proyectos MCyT (1FD97-0551), de la Generalitat Valenciana (02-046) y de la Institució Alfons el Magnánim (02-046)Peer reviewe

The success of Quercus ilex plantations in agricultural fields in eastern Spain

Twenty-five years after planting, we measured the survival, growth and reproduction of 153 Quercus ilex plantations promoted by the afforestation programme of the European Union’s Common Agricultural Policy in agricultural fields in the east of the Iberian Peninsula, as a function of climatic aridity and stand characteristics related to water supply and competition among trees for water. Using field sampling, we found that, on average, 80% of the trees in plantations survived, more than 55% had already produced acorns and the tallest tree in each field exceeded 4 m, which are all higher values than those reported for forest plantations of this species in the same area and which represent the overcoming of the limitations imposed by climatic aridity on the natural regeneration of the species. A small proportion of the variation in all success variables was explained by water-related plantation characteristics, such as planting density, drought intensity in the year after planting, and soil permeability. However, climatic aridity only influenced the proportion of reproductive trees, but not the other variables of plantation success. However, most of the variation in planting success variables was linked to who owned the field, which nursery produced the seedlings, and the year of planting. Our results support the idea that the deep soils of agricultural fields counteract the negative effect of climatic aridity on plant performance, but that it is necessary to standardise nursery and planting practices, adapt planting density to the environmental characteristics of the site and provide irrigation supply in the early years to ensure the success of future plantations

Somatostatin Receptor Splicing Variant sst5TMD4 Overexpression in Glioblastoma Is Associated with Poor Survival, Increased Aggressiveness Features and Somatostatin Analogs Resistance

Glioblastoma (GBM) is the most malignant and lethal brain tumor. Current standard treatment consists of surgery followed by radiotherapy/chemotherapy; however, this is only a palliative approach with a mean post-operative survival of scarcely ~12–15 months. Thus, the identification of novel therapeutic targets to treat this devastating pathology is urgently needed. In this context, the truncated splicing variant of the somatostatin receptor subtype 5 (sst5TMD4), which is produced by aberrant alternative splicing, has been demonstrated to be overexpressed and associated with increased aggressiveness features in several tumors. However, the presence, functional role, and associated molecular mechanisms of sst5TMD4 in GBM have not been yet explored. Therefore, we performed a comprehensive analysis to characterize the expression and pathophysiological role of sst5TMD4 in human GBM. sst5TMD4 was significantly overexpressed (at mRNA and protein levels) in human GBM tissue compared to non-tumor (control) brain tissue. Remarkably, sst5TMD4 expression was significantly associated with poor overall survival and recurrent tumors in GBM patients. Moreover, in vitro sst5TMD4 overexpression (by specific plasmid) increased, whereas sst5TMD4 silencing (by specific siRNA) decreased, key malignant features (i.e., proliferation and migration capacity) of GBM cells (U-87 MG/U-118 MG models). Furthermore, sst5TMD4 overexpression in GBM cells altered the activity of multiple key signaling pathways associated with tumor aggressiveness/progression (AKT/JAK-STAT/NF-κB/TGF-β), and its silencing sensitized GBM cells to the antitumor effect of pasireotide (a somatostatin analog). Altogether, these results demonstrate that sst5TMD4 is overexpressed and associated with enhanced malignancy features in human GBMs and reveal its potential utility as a novel diagnostic/prognostic biomarker and putative therapeutic target in GBMs