A. Aldezábal

El papel de los herbívoros en la conservación de los pastos

El Procambarus clarkii (cangrejo de rio americano o cangrejo rojo de las marismas) es un ejemplo de la introduccion de una especie en un ecosistema. En este trabajo se utiliza una poblacion de esta especie en la isla de Tenerife para un conjunto de actividades educativas en un Instituto de Formacion Profesional. Estas actividades incluyen muestreos y capturas de los cangrejos en el campo, la toma de sus medidas iniciales y su mantenimiento en el Instituto.Resumen de Tesis Doctoral. Director: Emilio Chuvieco Salinero. Centro: Departamento de Geografia, Programa interdepartamental de doctorado en Ciencias Ambientales. Fecha de lectura: 22 de Marzo de 2002.Francisco Diaz Pineda (pacopi@bio.ucm.es) es Catedratico de Ecologia en la Universidad Complutense de Madrid desde 1981. Estudio Biologia en la Universidad de Sevilla con ‘premio extraordinario’ (1973). Doctorado en 1975, su experiencia se basa en la planificacion territorial, el estudio de las bases ecologicas de la conservacion de la naturaleza, el analisis de ecosistemas mediterraneos - principalmente de pastizal - y la regulacion de la diversidad biologica. Es el actual Presidente de WWF–Espana (Adena) y miembro del International Board of WWF. Es miembro fundador del Centro Europeo de Conservacion de la Naturaleza (Ecnc) en Tilburg (Holanda) y componente de su actual Consejo Cientifico. Tambien es miembro del Capitulo espanol del Club de Roma desde 1999. Autor y editor de varios libros y monografias especializados, tiene 150 trabajos cientificos publicados y un centenar de articulos de divulgacion cientifica y opinion. Ha desarrollado 70 proyectos aplicados de ecologia por encargos o concursos nacionales, extranjeros o internacionales. Los premios recibidos incluyen el ‘Osborne’ (1975), el ‘Medio Ambiente sobre Estudios Tematicos’ (1984), el ’Ayuntamiento de Madrid’ (1986) y el ‘Premio Nacional de Medio Ambiente’ (2000). Jose Maria Rey Benayas le hizo la siguiente entrevista.

Understorey foraging and habitat selection by sheep in mixed Atlantic woodland

Abstract. The main objectives of this study were to investigate sheep foraging behaviour in mixed Atlantic woodland and to assess its impact on the forest understorey. We established 89 plots along four forest types: Fagus woodland, Quercus woodland, riparian gallery forest and conifer plantations. The presence of plant species in the forest understorey and their foraging damage was surveyed bimonthly from July 1996 to June 1997. In addition, we estimated the selection of woodland types by sheep through the pellet-group count technique. The intensity of foraging by sheep was negligible for most of the plant species, however several species showed substantial damage in some woodland types. Among the species that were abundant and widespread in the entire study area, Rubus ulmifolius, graminoids and Ilex aquifolium were consumed most. Sheep selected only larch plantations, where grasses and Rubus were very abundant. This grazing behaviour reduced browsing damage of the understorey of woodland stands with higher conservation value, such as Quercus and Fagus woodlands.

Influence of Snowmelt Timing on the Diet Quality of Pyrenean Rock Ptarmigan (Lagopus muta pyrenaica): Implications for Reproductive Success

The Pyrenean rock ptarmigan (Lagopus muta pyrenaica) is the southernmost subspecies of the species in Europe and is considered threatened as a consequence of changes in landscape, human pressure, climate change, and low genetic diversity. Previous studies have shown a relationship between the date of snowmelt and reproductive success in the Pyrenean ptarmigan. It is well established that birds laying early in the breeding season have higher reproductive success, but the specific mechanism for this relationship is debated. We present an explicative model of the relationship between snowmelt date and breeding success mediated by food quality for grouse in alpine environments. From microhistological analyses of 121 faecal samples collected during three years in the Canigou Massif (Eastern Pyrenees), and the assessment of the chemical composition of the main dietary components, we estimated the potential quality of individual diets. Potential dietary quality was correlated with free-urate faecal N, a proxy of the digestible protein content ingested by ptarmigan, and both were correlated with phenological stage of consumed plants, which in turn depends on snowmelt date. Our findings suggest that the average snowmelt date is subject to a strong interannual variability influencing laying date. In years of early snowmelt, hens benefit from a longer period of high quality food resources potentially leading to a higher breeding success. On the contrary, in years of late snowmelt, hens begin their breeding period in poorer nutrient condition because the peaks of protein content of their main food items are delayed with respect to laying date, hence reducing breeding performance. We discuss the possible mismatch between breeding and snowmelt timing.

Grazing exclusion unleashes competitive plant responses in Iberian Atlantic mountain grasslands

Questions Does the absence of equalizing mechanisms after cessation of grazing unleash strong aboveground competitors to create large patches in the community? Do these competitive intraspecific aggregations displace and exclude other species, thereby reducing species diversity? Location Atlantic grasslands in the Aralar Natural Park, Basque Country, Northern Iberian Peninsula. Methods Large herbivores were experimentally excluded from three sites (50 m × 50 m exclusion fences) during nine years in a productive semi-natural grassland system with long history of grazing, using adjacent grazed plots as experimental controls. Sampling was carried out by placing systematically one hundred quadrats (0.5 m × 0.5 m) in each of the six plots. Floristic composition and abundance, as well as eight hydrological and chemical soil properties, were measured in each quadrat. The spatial structures created by competitive species were analysed using Redundancy analysis in conjunction with Morans Eigenvector Maps, and soil variables were simultaneously included in the analyses, thus disentangling the structures likely created by niche effects. Competitive exclusion was further determined using linear regressions between species richness and abundance of competitive species. Results Grazing exclusion unleashed competitive species such as Festuca rubra and Agrostis capillaris, which became dominant in the exclusion plots and created large spatial patches. Furthermore, a negative linear relationship, consistent across exclusion plots, was observed between species richness and abundance of competitive species, indicating that strong aboveground competitors outcompeted other species when herbivores were excluded. However, the outcome of grazing exclusion across sites depended to some extent on local environmental conditions (niche effects). Conclusions This work confirms that the powerful equalizing mechanism of disturbance by herbivores is crucial for species co-existence in productive grasslands. However, important differences observed in environmental effects across sites suggest that, even in highly productive grasslands, plant traits and local environmental characteristics (niche effects) do matter for species co-existence. This article is protected by copyright. All rights reserved.

State-Space Modelling of the Drivers of Movement Behaviour in Sympatric Species

Understanding animal movement behaviour is key to furthering our knowledge on intra- and inter-specific competition, group cohesion, energy expenditure, habitat use, the spread of zoonotic diseases or species management. We used a radial basis function surface approximation subject to minimum description length constraint to uncover the state-space dynamical systems from time series data. This approximation allowed us to infer structure from a mathematical model of the movement behaviour of sheep and red deer, and the effect of density, thermal stress and vegetation type. Animal movement was recorded using GPS collars deployed in sheep and deer grazing a large experimental plot in winter and summer. Information on the thermal stress to which animals were exposed was estimated using the power consumption of mechanical heated models and meteorological records of a network of stations in the plot. Thermal stress was higher in deer than in sheep, with less differences between species in summer. Deer travelled more distance than sheep, and both species travelled more in summer than in winter; deer travel distance showed less seasonal differences than sheep. Animal movement was better predicted in deer than in sheep and in winter than in summer; both species showed a swarming behaviour in group cohesion, stronger in deer. At shorter separation distances swarming repulsion was stronger between species than within species. At longer separation distances inter-specific attraction was weaker than intra-specific; there was a positive density-dependent effect on swarming, and stronger in deer than in sheep. There was not clear evidence which species attracted or repelled the other; attraction between deer at long separation distances was stronger when the model accounted for thermal stress, but in general the dynamic movement behaviour was hardly affected by the thermal stress. Vegetation type affected intra-species interactions but had little effect on inter-species interactions. Our modelling approach is useful in interpreting animal interactions, in order to unravel complex cooperative or competitive behaviours, and to the best of our knowledge is the first modelling attempt to make predictions of multi-species animal movement under different habitat mosaics and abiotic environmental conditions.