María José Albert

Structural equation modelling: an alternative for assessing causal relationships in threatened plant populations

Structural equation modelling (SEM) is a powerful tool to explore and contrast hypotheses on causal relationships among variables using observational data. It constitutes an alternative to experimental approaches that is especially useful in the conservation of small populations where the implementation of treatments may have a negative effect on population viability. We are presently applying SEM to study the factors that condition reproductive success, seed emergence and plantlet survival in several plant species. We are also using model comparisons through multi-sample analysis to assess the implications of different microhabitats on the viability of a population. The most outstanding advantages of this tool are the global perspective used in the study of complex problems, the ability to discern the essential from the accessory, and the possibility of evaluating ones own hypotheses. The basic procedure, the limitations of this method and further applications in conservation and management are also discussed.

Small-scale demographic compensation in a high-mountain endemic: the low edge stands still

Background: Under the current warming process, with its implications of higher temperatures, less rainfall, snowfall and snow cover, low-edge populations of high-mountain plants are expected to decline. Demographic studies are useful to foresee the future dynamics of species ranges. Adaptation, phenotypic plasticity, and demographic compensation have been proposed as mechanisms to cope with climate change. Aim: We studied the population dynamics of the high-mountain narrow endemic Armeria caespitosa at the extremes of its altitude distribution (low versus high edge), the high edge representing colonised summits that provide optimal growing conditions. The focus of the study was to establish if the species is retracting at its lower distribution range. Methods: We used 4 years of population censuses and soil seed bank data. Population matrix models allowed us to study the stochastic population growth rates, the species long-term viability under higher frequency of extreme years, and the life cycle transitions responsible for the differences in population dynamics between elevation range edges. Results: The low edge of the A. caespitosa elevation range appeared stable, with positive population growth rates under current environmental conditions, and a null quasi-extinction probability in the long-term under scenarios of high frequency of extremely dry years. Conclusions: The species will likely withstand the current climate-warming scenario along its elevation range. Results supported the role of so-called demographic compensation at a small spatial scale, which we argue might be common in the Mediterranean mountains.

Effects of temperature and pretreatments on seed germination of nine semiarid species from NE Spain

The aim of this work was to study the seed germination characteristics, under different incubation temperatures and using different pretreatments for promoting germination, of nine species, Boleum asperum (Pers.) Desvaux, Centaurea pinnata Pau, Halopeplis amplexicaulis (Vahl.) Ung.-Sternb, Krascheninnikovia ceratoides (L.) Gueldenst, Lythrum flexuosum Lag., Microcnemum coralloides (Loscos & Pardo) Buen, Pucinellia pungens (Pau) Paunero, Thymus loscosii Willk., and Vella pseudocytisus L. subsp. paui Gomez Campo, that grow in semiarid regions of NE Spain. In eight of these species, seeds collected from several (2-9) populations were tested. Constant 15 C, 20 C, or 25 C, and alternating 15/25 C temperature regimes and 16/8 hours light/dark photoperiod conditions were used. In seeds from the different populations of Halopeplis amplexicaulis and Microcnemum coralloides, manual scarification, dry heat, and soaking in gibberellic acid solution were used as pretreatments applied for enhancing germination. Germina...

Does habitat structure matter? Spatially explicit population modelling of an Iberian gypsum endemic

Habitat heterogeneity may influence plant demography because conditions for survival, growth, and reproduction vary within a species’ range. We assessed the role of microhabitat spatial structure on the demography of Helianthemum squamatum, a shrubby gypsum specialist endemic to the Iberian Peninsula. We evaluated the demographic effect of microhabitat spatial variation using an approach that combined cellular automata with matrix population models, and included environmental and demographic stochasticty. We collected data on seed bank (2003–2005), seedling emergence (2003–2006), and adult survivorship (2004–2007) for H. squamatum in two independent blocks with different grazing intensity in Belinchón (Cuenca, Spain). We built spatial scenarios for each block based on field data of cover and spatial pattern of four microhabitats: lichenic crust, litter, H. squamatum, and shrub. Seedling survivorship was affected by year, block, and microhabitat, with individuals emerging under conspecifics having the highest survival rate and on litter the lowest in both blocks, whereas the effect of crust and other shrubs differed across blocks. Our models indicated population increase in the block with low grazing, but population decline in the block with intense grazing. We hypothesize that higher pressure of livestock grazing and trampling leads to a shift in relative microhabitat suitability for crust and shrub. This potential effect of grazing on spatial demographic variation opens interesting questions for future research. We emphasize the importance of considering microhabitat spatial structure when evaluating management and conservation strategies.

Female reproductive output in a Mediterranean shrub: effects from inflorescence to population.

Inflorescence effects have been poorly studied, in spite of the functional relevance of the inflorescence in fruit and seed ecology. The present study focused on the effects of inflorescence size and phenology, and flower position within the inflorescence, in relation to fruit and seed production of the Mediterranean shrub Ononis fruticosa. Variability in fruit and seed production, seed weight and germination were estimated and modelled. Results confirmed that the most important predictors in seed production were inflorescence flowering time and flower position within the inflorescence. Thus, the number of mature seeds per fruit was higher in earlier inflorescences and in basal positions. On the other hand, predation was higher in fruits in basal positions. In fact, seed predation seemed to be the most important factor controlling final seed production. Models at the plant level suggested a negative incidence of geitonogamous pollination and resource limitation, which were also observed at the fruit level. This study confirmed the relevance of inflorescence effects on the reproductive output of O. fruticosa. Although the underlying processes could not be identified, our results provide several hypotheses for future experimental studies.

Assessing seed and microsite limitation on population dynamics of a gypsophyte through experimental soil crust disturbance and seed addition

Understanding the factors limiting population growth is crucial for species management and conservation. We assessed the effects of seed and microsite limitation, along with climate variables, on Helianthemum squamatum, a gypsum soil specialist, in two sites in central Spain. We evaluated the effects of experimental seed addition and soil crust disturbance on H. squamatum vital rates (survival, growth and reproduction) across four years. We used this information to build integral projection models (IPMs) for each combination of management (seed addition or soil disturbance), site and year. We examined differences in population growth rate (λ) due to management using life table response experiments. Soil crust disturbance increased survival of mid to large size individuals and germination. Contributions to λ of positive individual growth (progression) and negative individual growth (retrogression) due to managements varied among years and sites. Soil crust disturbance increased λ in the site with the highest plant density, and seed addition had a moderate positive effect on λ in the site with lowest plant density. Population growth rate (λ) decreased by half in the driest year. Differences in management effects between sites may represent a shift from seed to microsite limitation at increasing densities. This shift underscores the importance of considering what factors limit population growth when selecting a management strategy.

Biología de Conservación, nuevas estrategias bajo diferentes perspectivas

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.