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Soil fauna play a key role in nutrient cycling and decomposition, and in recent years researchers have become more and more interested in this compartment of terrestrial ecosystems. In addition, soil fauna can act as ecosystem engineers by creating, modifying and maintaining the habitat for other organisms. Ecologists usually utilize alive catches in pitfalls traps as a standard method to study the activity of epigeic fauna in addition to relative abundance. Counts in pitfall traps can be used as estimates of relative activity to compare among experimental treatments. This requires taking independent estimates of abundance (e.g.: by sifting soil litter, mark-recapture), which can then be used as covariates in linear models to compare the levels of fauna activity (trap catches) among treatments. However, many studies show that the use of pitfall traps is not the most adequate method to estimate soil fauna relative abundances, and these concerns may be extensible to estimating activity. Here, we present two new types of traps devised to study activity in litter fauna, and which we call “cul-de-sac” and “basket traps” respectively. We experimentally show that, at least for litter dwellers, these new traps are more appropriate to estimate fauna activity than pitfall traps because: 1) Pitfall traps contain 3.5x more humidity than the surrounding environment, potentially attracting animals towards them when environmental conditions are relatively dry, 2) cul-de-sac and basket traps catch ca. 4x more both meso- and macrofauna than pitfall traps, suggesting that pitfall traps are underestimating activity; and 3) pitfall traps show a bias towards collecting 1.5x higher amounts of predators, which suggests that predation rates are higher within pitfall traps. We end with a protocol and recommendations for how to use these new traps in ecological experiments and surveys aiming at estimating soil arthropod activity.

Soil fauna play a key role in nutrient cycling and decomposition, and in recent years, researchers have become more and more interested in this compartment of terrestrial ecosystems. In addition, soil fauna can act as ecosystem engineers by creating, modifying, and maintaining the habitat for other organisms. Ecologists usually utilize live catches in pitfalls traps as a standard method to study the activity of epigeic fauna in addition to relative abundance. Counts in pitfall traps can be used as estimates of relative activity to compare among experimental treatments. This requires taking independent estimates of abundance (e.g., by sifting soil litter, mark–recapture), which can then be used as covariates in linear models to compare the levels of fauna activity (trap catches) among treatments. However, many studies show that the use of pitfall traps is not the most adequate method to estimate soil fauna relative abundances, and these concerns may be extensible to estimating activity. Here, we present two new types of traps devised to study activity in litter fauna, and which we call “cul-de-sac” and “basket traps”, respectively. We experimentally show that, at least for litter dwellers, these new traps are more appropriate to estimate fauna activity than pitfall traps because: (1) pitfall traps contain 3.5× more moisture than the surrounding environment, potentially attracting animals towards them when environmental conditions are relatively dry; (2) cul-de-sac and basket traps catch ca. 4× more of both meso- and macrofauna than pitfall traps, suggesting that pitfall traps are underestimating activity; and (3) pitfall traps show a bias towards collecting 1.5× higher amounts of predators, which suggests that predation rates are higher within pitfall traps. We end with a protocol and recommendations for how to use these new traps in ecological experiments and surveys aiming at estimating soil arthropod activity

Soil invertebrates inhabiting the leaf litter layer of beech forests –essentially primary and secondary decomposers and their predators– contribute, through their activities, to important ecosystem processes such as leaf litter decomposition and nutrient turnover. In order to better understand the structure and dynamics of the soil food web, and anticipate the potential consequences that environmental alterations can have on its functioning, investigating what factors determine the distribution of soil fauna and influence its maintenance, is crucial. The objectives of this thesis are 1) to examine the spatial structure of the different functional groups within the soil food web at different spatial scales, and determine the effect of abiotic factors such as precipitation in the configuration of soil communities, 2) to explore the trophic ecology of soil oribatid mites in relation to water availability through their isotopic signatures, 3) to investigate the role played by large soil predators in regulating lower trophic levels and the associated rate of leaf litter decomposition in both wet and dry beech forests, as well as 4) the role of beech cupules in the distribution of soil fauna, as keystone structures that contribute to its maintenance by acting as moist shelters during droughts. The results indicate that soil fauna displays spatially aggregated patterns over multiple scales, at both regional and micro-local scales, that can be explained by different abiotic and biotic factors. First, wet-rich micro-sites located at the base of slopes, where water, leaf litter and nutrients accumulate, exhibit greater abundances of fauna. Second, there are more invertebrates in the leaf litter layer of rainy beech forests and in patches with higher soil moisture, which suggests that water availability is a fundamental factor in the configuration and maintenance of the decomposer community. A higher water availability in the soil leads to greater microbial biomass and reduced

Facilitative or positive interactions are ubiquitous in nature and play a fundamental role in the configuration of ecological communities. In particular, habitat modification and niche construction, in which one organism locally modifies abiotic conditions and favours other organisms by buffering the effects of adverse environmental factors, are among the most relevant facilitative interactions. In line with this, ‘keystone structures’, which provide resources, refuge, or advantageous services decisive for other species, may allow the coexistence of various species and thus considerably contribute to diversity maintenance. Beech cupules are woody husks harbouring beech fruits that remain in the forest soil for relatively long periods of time. In this study, we explored the potential role of these cupules in the distribution and maintenance of the soil fauna inhabiting the leaf litter layer. We experimentally manipulated cupule availability and soil moisture in the field to determine if such structures are limiting and can provide moist shelter to soil animals during drought periods, contributing to minimize desiccation risks. We measured invertebrate abundances inside relative to outside the cupules, total abundances in the leaf litter and animal body sizes, in both dry and wet experimental plots. We found that these structures are preferentially used by the most abundant groups of smaller soil animals—springtails, mites and enchytraeids—during droughts. Moreover, beech cupules can be limiting, as an increase in use was found with higher cupule densities, and are important resources for many small soil invertebrates, driving the spatial structure of the soil community and promoting higher densities in the leaf litter, probably through an increase in habitat heterogeneity. We propose that fruit woody structures should be considered ‘keystone structures’ that contribute to soil community maintenance. Therefore, beech trees may indirectly facilitate soil fauna activiti

El canibalismo sexual es un comportamiento extremo en el que las hembras generalmente matan y se alimentan del macho antes, durante o tras el apareamiento, y puede imponer elevados costes reproductores sobre los machos y las hembras. El balance de costes y beneficios dependerá del momento del canibalismo respecto a la cópula, y tendrá la máxima implicación si los individuos que participan en la interacción caníbal aún no se han apareado ya que, si la hembra no encuentra más machos, ninguno de los dos individuos podrá producir descendencia. El canibalismo sexual también puede afectar a la eficacia biológica de las hembras caníbales ya apareadas, cuando la poliandria (la hembra se empareja con más de un macho) contribuye a que la descendencia tenga mayor viabilidad. Sin embargo, si la hembra obtiene un beneficio alimentario y puede conseguir machos adicionales para aparearse, el canibalismo sexual se convierte en un conflicto de intereses extremo, dado que la hembra puede querer canibalizar al macho, mientras que está en el interés de éste último conseguir escapar para copular con otras hembras, Este fuerte conflicto ha hecho que los investigadores se pregunten por el origen evolutivo del canibalismo sexual pre-cópula y su mantenimiento en las poblaciones naturales. Ello ha originado recientemente la interpretación del canibalismo sexual como un síndrome comportamental, en que las hembras vírgenes matarían al macho no por necesidades nutricionales, sino porque las hembras más agresivas pueden haber sido seleccionadas por el hecho de que una mayor agresividad (o voracidad) lleva a una mayor tasa de crecimiento y fecundidad, y al ataque indiscriminado a los machos por un simple lastre (o salpicadura) genético/a. Contrasta con esta idea el hecho de que se comprueba frecuentemente que las hembras de especies caníbales no atacan a los machos hasta que se han asegurado el esperma o sólo si la escasez de alimento es considerable. En la presente tesis se aportó información pa

El Cambio Climático inducido por la actividad del hombre produce alteraciones de los valores medios de la temperatura que pueden afectar tanto a multitud de interacciones ecológicas como a la expresión génica de caracteres y su evolución por selección natural. Se utilizó un Modelo Basado en Individuos (IBM) semi-espacialmente explícito que simula las dinámicas eco-evolutivas de una cadena trófica de la hojarasca del suelo, típica de hayedos (Fagus sylvatica) para realizar un estudio de la fuerza y dirección de la selección natural bajo diferentes condiciones ambientales (abióticas y bióticas). Dicha cadena trófica incluye tres niveles tróficos diferentes, una especie de depredador, otra de presa y una especie de recurso basal. Tanto los depredadores como las presas presentan 13 rasgos funcionales, de los cuales 4 son plásticos con la temperatura. Todos los rasgos tienen una genética cuantitativa basada en diversos niveles de correlación genética entre rasgos y diversos rangos de variación de los mismos por selección natural. Bajo este marco se evaluaron los gradientes de selección natural en 32 combinaciones, modificando la arquitectura genética de las presas y de los depredadores (dos niveles de correlación genética entre los rasgos: =0.1 y =0.9), el rango de variación de los rasgos (bajo y alto),así como, los agentes de selección (dos temperaturas: 16C y 25C y presencia/ausencia de depredadores). También se analizó la selección direccional diferencial entre ambientes (16C, 20C ó 25C y presencia/ausencia de depredadores) y arquitectura genética variable. Se encontró que la temperatura, tanto directa o indirectamente, actúa como un agente de selección -muy importante sobre los rasgos dependientes de la temperatura- tales como la tasa metabólica o la tasa de crecimiento. Además, los procesos de selección lineal y no lineal inducidos por los agentes de selección (temperatura y presencia/ausencia de depredadores) dependen de la arquitectura genética de las presa

El funcionamiento de los ecosistemas puede depender en gran medida de la diversidad de interacciones entre las especies que los integran, dentro de lo que conocemos como redes ecológicas. Debido a ello, el cambio climático puede afectar a los procesos ecosistémicos tanto de manera directa (ej. un descenso en la precipitación afecta negativamente a las tasas de descomposición) como de manera indirecta mediante su efecto en la magnitud y dirección de las interacciones en dichas redes ecológicas. Por lo tanto estudiar cómo la variabilidad climática puede afectar a la diversidad de especies, las interacciones entre ellas y como esto afecta al funcionamiento de los ecosistemas, es de suma importancia para entender los efectos del cambio climático. Esto es especialmente importante en los ecosistemas amenazados de nuestros espacios naturales protegidos, como es el caso del hayedo en los parques nacionales, dado que allí el haya se halla en el límite sur de su distribución europea y podría estar en regresión debido al descenso de las precipitaciones como consecuencia del cambio climático. Presentamos los primeros resultados de un proyecto multidisciplinar en tres parques nacionales (Aigüestortes, Ordesa y Picos de Europa) en el que utilizamos ADN de código de barras para identificar especies y haplotipos concretos de depredadores (arañas) y presas (colémbolos) y medimos la estructura espacial de la abundancia de los principales grupos funcionales de meso y macrofauna de las redes tróficas de la hojarasca de los hayedos, la cual está involucrada en un importante proceso ecosistémico: la descomposición de la hojarasca y el consecuente reciclado de nutrientes en el bosque. Se examinaron los componentes de la varianza espacial para la abundancia de los principales grupos funcionales presentes en la hojarasca y se analizaron los posibles factores que controlan la estructura espacial de cada uno de ellos. La red trófica de la hojarasca exhibe una fuerte estructura espacial, funda

[Background]: Explanations for the evolution of female-biased, extreme Sexual Size Dimorphism (SSD), which has puzzled researchers since Darwin, are still controversial. Here we propose an extension of the Gravity Hypothesis (i.e., the GH, which postulates a climbing advantage for small males) that in conjunction with the fecundity hypothesis appears to have the most general power to explain the evolution of SSD in spiders so far. In this "Bridging GH" we propose that bridging locomotion (i.e., walking upside-down under own-made silk bridges) may be behind the evolution of extreme SSD. A biomechanical model shows that there is a physical constraint for large spiders to bridge. This should lead to a trade-off between other traits and dispersal in which bridging would favor smaller sizes and other selective forces (e.g. fecundity selection in females) would favor larger sizes. If bridging allows faster dispersal, small males would have a selective advantage by enjoying more mating opportunities. We predicted that both large males and females would show a lower propensity to bridge, and that SSD would be negatively correlated with sexual dimorphism in bridging propensity. To test these hypotheses we experimentally induced bridging in males and females of 13 species of spiders belonging to the two clades in which bridging locomotion has evolved independently and in which most of the cases of extreme SSD in spiders are found. [Results]: We found that 1) as the degree of SSD increased and females became larger, females tended to bridge less relative to males, and that 2) smaller males and females show a higher propensity to bridge. [Conclusions]: Physical constraints make bridging inefficient for large spiders. Thus, in species where bridging is a very common mode of locomotion, small males, by being more efficient at bridging, will be competitively superior and enjoy more mating opportunities. This "Bridging GH" helps to solve the controversial question of what keeps mal

[Background] Animals have been hypothesized to benefit from pendulum mechanics during suspensory locomotion, in which the potential energy of gravity is converted into kinetic energy according to the energy-conservation principle. However, no convincing evidence has been found so far. Demonstrating that morphological evolution follows pendulum mechanics is important from a biomechanical point of view because during suspensory locomotion some morphological traits could be decoupled from gravity, thus allowing independent adaptive morphological evolution of these two traits when compared to animals that move standing on their legs; i.e., as inverted pendulums. If the evolution of body shape matches simple pendulum mechanics, animals that move suspending their bodies should evolve relatively longer legs which must confer high moving capabilities., [Methodology/Principal Findings] We tested this hypothesis in spiders, a group of diverse terrestrial generalist predators in which suspensory locomotion has been lost and gained a few times independently during their evolutionary history. In spiders that hang upside-down from their webs, their legs have evolved disproportionately longer relative to their body sizes when compared to spiders that move standing on their legs. In addition, we show how disproportionately longer legs allow spiders to run faster during suspensory locomotion and how these same spiders run at a slower speed on the ground (i.e., as inverted pendulums). Finally, when suspensory spiders are induced to run on the ground, there is a clear trend in which larger suspensory spiders tend to run much more slowly than similar-size spiders that normally move as inverted pendulums (i.e., wandering spiders)., [Conclusions/Significance] Several lines of evidence support the hypothesis that spiders have evolved according to the predictions of pendulum mechanics. These findings have potentially important ecological and evolutionary implications since they could partially explain the occurrence of foraging plasticity and dispersal constraints as well as the evolution of sexual size dimorphism and sociality.