Modeling shrub encroachment in subalpine grasslands under different environmental and management scenarios.

Woody plants are spreading in many alpine and subalpine ecosystems and are expected to continue increasing in response to land abandonment and global warming. This encroachment threatens species diversity, and considerable efforts have been deployed to control it. In this study, we combined a lattice model and field data to investigate the efficiency of different management strategies in controlling shrub encroachment in alpine grasslands. The model parameter values were estimated in the field based on the thorny shrub Echinospartum horridum (erizón) which is currently encroaching in central Spanish Pyrenees. Our study shows that encroachment could accelerate if climate warming continues. Different management scenarios consisting of a gradient of livestock pressures, fire events and mechanical removal were simulated to identify scenarios able to control the expansion of shrubs into grasslands. Our study shows that grazing alone cannot stop encroachment. Rather, a combination of grazing and shrub removal (either by fire or mechanical removal) is needed, and our model can help estimate the frequency and intensities of the shrub removal. This model can be used to investigate the consequences of different management scenarios and environmental variability which could be of practical value in the preservation of alpine grasslands.

The role of reproductive plant traits and biotic interactions in the dynamics of semi-arid plant communities.

The dynamics of semi-arid plant communities are determined by the interplay between competition and facilitation among plants. The sign and strength of these biotic interactions depend on plant traits. However, the relationships between plant traits and biotic interactions, and the consequences for plant communities are still poorly understood. Our objective here was to investigate, with a modelling approach, the role of plant reproductive traits on biotic interactions, and the consequences for processes such as plant succession and invasion. The dynamics of two plant types were modelled with a spatially-explicit integrodifferential model: (1) a plant with seed dispersal (colonizer of bare soil) and (2) a plant with local vegetative propagation (local competitor). Both plant types were involved in facilitation due to a local positive feedback between vegetation biomass and soil water availability, which promoted establishment and growth. Plants in the system also competed for limited water. The efficiency in water acquisition (dependent on reproductive and growth plant traits) determined which plant type dominated the community at the steady state. Facilitative interactions between plant types also played an important role in the community dynamics, promoting establishment in the driest conditions and recovery from low biomass. Plants with vegetative propagation took advantage of the ability of seed dispersers to establish on bare soil from a low initial biomass. Seed dispersers were good invaders, maintained high biomass at intermediate and high rainfall and showed a high ability in taking profit from the positive feedback originated by plants with vegetative propagation under the driest conditions. However, seed dispersers lost competitiveness with an increasing investment in fecundity. All together, our results showed that reproductive plant traits can affect the balance between facilitative and competitive interactions. Understanding this effect of plant traits on biotic interactions provides insights in processes such as plant succession and shrub encroachment.

Differences in gypsum plant communities associated with habitat fragmentation and livestock grazing.

The negative consequences of habitat fragmentation for plant communities have been documented in many regions of the world. In some fragmented habitats, livestock grazing has been proposed to be a dispersal mechanism reducing isolation between fragments. In others, grazing acts together with fragmentation in a way that increases habitat degradation. Iberian gypsum plant communities have been grazed and fragmented by agricultural practices for centuries. Although their conservation is considered a priority by the European Community, the effects of fragmentation on gypsum plant communities and the possible role of livestock grazing remain unknown. In addition, a substantial proportion of plant species growing in gypsum environments are gypsum specialists. They could be particularly affected by fragmentation, as was found for other habitat specialists (i.e., serpentine and calcareous specialists). In this study (1) we investigated the effect of fragmentation and grazing on gypsum plant community composition (species and life-forms), and (2) we tested to see if gypsum specialists were differently affected by fragmentation and grazing than habitat generalists. A vegetation survey was conducted in the largest gypsum outcrop of Europe (Middle Ebro Valley, northeast Spain). Fragmented and continuous sites in grazed and ungrazed areas were compared. Measurements related to species and composition of life-forms were contrasted first for the whole gypsum plant community and then specifically for the gypsum specialists. In the whole community, our results showed lower plant species diversity in fragmented sites, mainly due to the larger dominance of species more tolerant to fragmented habitat conditions. With livestock grazing, the plant species richness and the similarity in plant species composition between remnants was larger, suggesting that animals were acting as dispersal agents between fragments. As expected, gypsum specialists were less abundant in fragmented areas, and grazing led to the disappearance of the rare gypsum specialist Campanula fastigiata. According to our results, conservation strategies for gypsum plant communities in human-dominated landscapes should consider that fragmentation and grazing modify plant community composition affecting gypsum specialists in particular.

Aggressive behaviour, sexual strategies and their relation to age in male Spanish ibex (Capra pyrenica ).

This study aimed to investigate the factors determining male reproductive success during the rutting season of the Spanish ibex. The rut lasts about seven weeks. At the begining of this period the old males engage in contests with each other, while the adult and subadult males spend more time courting the females. In the second half of this period, the old males court and gain reproductive acceptance while the adult and subadult males decrease their courtship activity. The old males also differ from the adult and subadults in the daily pattern of courtship activity. The old males test their relative strength and show agonistic displays as their most typical behaviour, while younger males tend towards more overt and primitive forms of fighting. Most contests involving males of all age classes occur between animals of similar age and these combats often end unresolved. The older of two combatants usually wins. Older males are preferred to younger ones by the females. The older the males, the more energy they expend in activities leading to mating and representing energy expenditure and the less time they use in those representing energy saving or recovery.