Lloret F, Piñol J, Castellenou M (2009) Wildfires. In: J. Woodward (ed.). The Physical Geography of the Mediterranean. Oxford University Press 541- 558.
Piñol J., Espadaler X., Cañellas N., Pérez N. (2009) Effects of the concurrent exclusion of ants and earwigs on aphid abundance in an organic citrus grove. BioControl. 54: 515-527.EnllaçDoi: 10.1007/s10526-008-9203-8
Based on the well-known mutualism between ants (Hymenoptera: Formicidae) and aphids (Homoptera: Aphididae), we conducted a five-year experiment of ant-exclusion from the canopies of citrus trees as a possible method of biological control of aphids. However, our results showed that the exclusion of ants from the canopies increased, instead of reducing, aphid abundance. To explain this unexpected result, we reasoned that the exclusion of ants from the canopies might also have excluded crawling insects that prey on aphids, such as the European earwig (Forficula auricularia L., Dermaptera: Forficulidae). Such a possibility is supported by the negative relationship between aphid density and the abundance of earwigs, consistent with a top-down control of aphids by earwigs. In contrast, the abundance of other aphid predators (Coleoptera: Coccinellidae, and Heteroptera) had no such negative effect on aphid density but a positive one, suggesting a bottom-up control, and showed no differences between control and ant-excluded trees. Thus, the most likely explanation for the increase in aphid abundance in the ant-excluded trees is the absence of earwigs from the canopies of the experimental trees, providing further evidence of the major role that earwigs play as control agents of aphids in cultivated trees. © International Organization for Biological Control (IOBC) 2008.
Piñol J., Espadaler X., Pérez N., Beven K. (2009) Testing a new model of aphid abundance with sedentary and non-sedentary predators. Ecological Modelling. 220: 2469-2480.EnllaçDoi: 10.1016/j.ecolmodel.2009.06.031
Aphid population dynamics has been thoroughly investigated, especially in tree-dwelling aphids. Among the controls of the aphid rate of increase are the negative effects of antagonists, the positive effects of mutualists, the density-dependence of the aphid dynamics, and the non-stationary quality of plant tissues. Here we present a mechanistic model of aphid growth that considers most of these governing factors using a simple formulation. What is new in this model is that it considers two kinds of antagonists. The first kind is a guild of aphid predator specialists that includes ladybirds (Coleoptera: Coccinellidae), but also species of some families of Hemiptera, Diptera, and Neuroptera. The second kind of antagonists consists of omnivores or generalist predators and in this particular setting is exemplified by the European earwig Forficula auricularia (Dermaptera: Forficulidae). The model developed here compared the effects of these two different kinds of aphid predators, the second one always at the site (sedentary predators) and the first one that arrives in important numbers only once the aphid population has already developed to some degree (non-sedentary predators). Multiple model parameter sets, representing different hypotheses about controls on aphid populations, were evaluated within the Generalised Likelihood Uncertainty Estimation (GLUE) methodology. The model correctly reproduced the experimental data obtained in an organic citrus grove showing the important effect that sedentary predators as earwigs can have on the aphid populations. Low densities of sedentary predators or even low predation rates can have a disproportionate effect on the final aphid density, as they prey on small populations, when the per capita effect on the aphid population is higher. During the main spring peak of aphids the role of non-sedentary predators is secondary, as they track the aphid density rather than control it. However, these non-sedentary predators are important within the proposed model to keep the second autumn peak of aphids at low values. © 2009 Elsevier B.V. All rights reserved.
Rodrigo A, Martínez-Vilalta J, Piñol J, Lloret F, Ribas A, Retana J, Losarcos J (2008) Disseny i aplicació d’una proposta d’aprenentatge cooperatiu dels continguts de l’àrea d’Ecologia mitjançant l’estudi de casos. En “Cap a l’espai europeu d’educació superior. Experiències docents innovadores de la UAB en ciències experimentals i tecnol ogies i en ciències de la salut”. Servei de Publicacions UAB. Bellaterra
Piñol J, Martínez-Vilalta J, Loepfe L, Mencuccini M (2008) Internalization of vertical transport in ecosystems: the xylem of woody plants. A: Valladares F, Camacho A, Elosegui A, Gracia C, Estrada M. Unity in diversity. Reflections on Ecology after the Legacy of Ramon Margalef. Bilbao. Fundación BBVA. pp. 393-425.
Poyatos R, Llorens P, Piñol J, Rubio C (2008) Response of Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) to soil and atmospheric water deficits under Mediterranean moutain climate. Annals of Forest Science 65: 306
Loepfe L., Martinez-Vilalta J., Piñol J., Mencuccini M. (2007) The relevance of xylem network structure for plant hydraulic efficiency and safety. Journal of Theoretical Biology. 247: 788-803.EnllaçDoi: 10.1016/j.jtbi.2007.03.036
The xylem is one of the two long distance transport tissues in plants, providing a low resistance pathway for water movement from roots to leaves. Its properties determine how much water can be transported and transpired and, at the same time, the plant's vulnerability to transport dysfunctions (the formation and propagation of emboli) associated to important stress factors, such as droughts and frost. Both maximum transport efficiency and safety against embolism have classically been attributed to the properties of individual conduits or of the pit membrane connecting them. But this approach overlooks the fact that the conduits of the xylem constitute a network. The topology of this network is likely to affect its overall transport properties, as well as the propagation of embolism through the xylem, since, according to the air-seeding hypothesis, drought-induced embolism propagates as a contact process (i.e., between neighbouring conduits). Here we present a model of the xylem that takes into account its system-level properties, including the connectivity of the xylem network. With the tools of graph theory and assuming steady state and Darcy's flow we calculated the hydraulic conductivity of idealized wood segments at different water potentials. A Monte Carlo approach was adopted, varying the anatomical and topological properties of the segments within biologically reasonable ranges, based on data available from the literature. Our results showed that maximum hydraulic conductivity and vulnerability to embolism increase with the connectivity of the xylem network. This can be explained by the fact that connectivity determines the fraction of all the potential paths or conduits actually available for water transport and spread of embolism. It is concluded that the xylem can no longer be interpreted as the mere sum of its conduits, because the spatial arrangement of those conduits in the xylem network influences the main functional properties of this tissue. This brings new arguments into the long-standing discussion on the efficiency vs. safety trade-off in the plants' xylem. © 2007 Elsevier Ltd. All rights reserved.
Piñol J., Castellnou M., Beven K.J. (2007) Conditioning uncertainty in ecological models: Assessing the impact of fire management strategies. Ecological Modelling. 207: 34-44.EnllaçDoi: 10.1016/j.ecolmodel.2007.03.020
A simple simulation model has been used to investigate whether large fires in Mediterranean regions are a result of extreme weather conditions or the cumulative effect of a policy of fire suppression over decades. The model reproduced the fire regime characteristics for a wide variety of regions of Mediterranean climate in California, France and Spain. The Generalised Likelihood Uncertainty Estimation (GLUE) methodology was used to assess the possibility of multiple model parameter sets being consistent with the available calibration data. The resulting set of behavioural models was used to assess uncertainty in the predictions. The results suggested that (1) for a given region, the total area burned is much the same whether suppression or prescribed fire policies are used or not; however fire suppression enhances fire intensity and prescribed burning reduces it; (2) the proportion of large fires can be reduced, but not eliminated, using prescribed fires, especially in areas which have the highest proportion of large fires. © 2007 Elsevier B.V. All rights reserved.
Poyatos R., Villagarcía L., Domingo F., Piñol J., Llorens P. (2007) Modelling evapotranspiration in a Scots pine stand under Mediterranean mountain climate using the GLUE methodology. Agricultural and Forest Meteorology. 146: 13-28.EnllaçDoi: 10.1016/j.agrformet.2007.05.003
Canopy transpiration (Ec) and soil evaporation (Es) in a Mediterranean Scots pine stand were simulated using a two-layer model, with a Jarvis-type submodel of canopy stomatal conductance (Gs) and a soil resistance to evaporation expressed as a function of superficial soil moisture. Sap flow measurements and soil evaporation data, together with meteorological and soil moisture variables were used to calibrate the model. Gs was calibrated using the generalized likelihood uncertainty estimation (GLUE) methodology, first with data from the year 2004, a year characterised by mild meteorological conditions. Then, data from the year 2003, which included an intense summer drought, was used to update the results from the previous calibration. The discrepancy between the diurnal courses of modelled and measured Ec using best-fit parameters was not related to any particular situation of meteorology or soil moisture. Model performance improved at the daily scale, but the model failed to simulate Ec adequately during the year 2005. Maximum modelled Es rates were 0.7 mm day-1 with the ratio Es/Ec being typically under 0.3 during the growing season. The GLUE analysis revealed that parameters representing reference stomatal aperture at a vapour pressure deficit (D) value equal to 1 kPa (Gs,ref), and sensitivity to D (m) were the most relevant, and were consistent with the hydraulic theory of stomatal regulation. Parameters controlling the response to superficial soil moisture deficit only appeared sensitive in the calibration with data from the year 2003, suggesting that response to deeper soil layers should also be considered in the model. Updating the original calibration reduced predictive uncertainty and constrained the value of some parameters. Nevertheless, it seems that representations of variable plant and soil hydraulic resistances, are required to simulate long-term Ec in seasonally-dry Mediterranean forest stands. © 2007 Elsevier B.V. All rights reserved.
Piñol J, Martínez-Vilalta J (2006) Ecología con números. Una introducción a la ecología con problemas y ejercicios de simulación. Lynx Edicions 450 pp
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