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Given the relevant role played by soil organisms in fundamental ecosystem processes, current ecological research stresses the importance of understanding the trophic structure of soil communities in order to better predict the effects that global environmental change can have on the soil food web structure and dynamics. Using stable isotope analysis, we examined the trophic ecology of six soil oribatid mite species present in the leaf litter of beech forests which mainly differed in mean annual precipitation. We explored the relationship between animal and leaf litter signatures to determine which of the two approaches, conventional calibration or a novel solution we offer using statistical control (i.e., isotopic signature of the basal resource included as a covariate in the model), is more adequate to evaluate the trophic structure of soil communities across different sites, and investigated if the trophic niches of the species varied under two different precipitation regimes. The trophic position of some species varied with rainfall; the observed enrichment in 15N in dry forests reflects trophic and spatial shifts probably resulting from changes in microbial activity and community composition. In addition, we find interactive effects between precipitation and the basal resource for some species and a lack of correlation between resource and oribatid mite stable isotope values for others. We discuss the pertinence of using conventional data calibration as it appears to mask relevant trends regarding the trophic ecology of oribatid mite species, and suggest using statistical control (a covariate approach) instead.

Shifts in densities of apex predators may indirectly affect fundamental ecosystem processes, such as decomposition, by altering patterns of cascading effects propagating through lower trophic levels. These top–down effects may interact with anthropogenic impacts, such as climate change, in largely unknown ways. We investigated how changes in densities of large predatory arthropods in forest leaf-litter communities altered lower trophic levels and litter decomposition. We conducted our experiment in soil communities that had experienced different levels of long-term average precipitation. We hypothesized that altering abundances of apex predators would have stronger effects on soil communities inhabiting dry forests, due to lower secondary productivity and greater resource overexploitation by lower trophic levels compared to wet forests. We experimentally manipulated abundances of the largest arthropod predators (apex predators) in field mesocosms replicated in the leaf-litter community of Iberian beech forests that differed in long-term mean annual precipitation by 25% (three dry forests with MAP 1,400 mm). After one year, we assessed abundances of soil fauna in lower trophic levels and indirect impacts on leaf-litter decomposition using litter of understorey hazel, Corylus avellana. Reducing densities of large predators had a consistently negative effect on final abundances of the different trophic groups and several taxa within each group. Moreover, large predatory arthropods strongly impacted litter decomposition, and their effect interacted with the long-term annual rainfall experienced by the soil community. In the dry forests, a 50% reduction in the densities of apex predators was associated with a 50% reduction in decomposition. In wet forests, the same reduction in densities of apex soil predators did not alter the rate of litter decomposition. Our results suggest that predators may facilitate lower trophic levels by indirectly reducing competition and resource overexploitation, cascading effects that may be more pronounced in drier forests where conditions have selected for greater competitive ability and more rapid resource utilization. These findings thus provide insights into the functioning of soil invertebrate communities and their role in decomposition, as well as potential consequences of soil community responses to climate change., This study has been funded by Spanish Ministry of Science and Innovation grants CGL2010‐18602, CGL2015‐66192‐R and Andalusian grant P12‐RNM‐1521‐EEZA to J.M.L.; the European Regional Development Fund, Agencia Nacional de la Promoción de Ciencia y Tecnología (PICT 2016‐1780), Argentina to A.T.A.; and FPI fellowship (BES‐2011‐043505) to N.M.‐R.

Crop production intensification often leads to the structural simplification of production systems. This structural simplification is expected to have strong impacts on biodiversity and the provisioning of ecosystem services, but information about this topic is scarce. For instance, no information exists for Mediterranean olive (Olea europaea) groves, despite olive farming representing a significant share of the agricultural sector in some European countries. We investigated the impact of in-farm and landscape-level structural simplification on the potential of three common insectivorous bats (i.e., Pipistrellus kuhlii, P. pygmaeus and P. pipistrellus) to provide biocontrol services against one of the most harmful olive pests worldwide, the olive fruit moth Prays oleae. Bats and insect surveys were both carried out in olive groves representing increasing levels of structural simplification and during three sampling seasons (spring, summer and autumn). At grove-level, structural simplification was considered as resulting from reduced planting pattern variability (i.e., tree and row spacing) and tree features (diameter at breast height, height of the trunk and canopy area), while at landscape level was considered as resulting from reduced land-cover types. We found that the Kuhl’s pipistrelle was the most frequently recorded species in all types of olive groves and seasons. Moreover, the activity levels of pipistrelle bats as a whole significantly decreased with the structural simplification of olive groves. The abundance of P. oleae was highest at intermediate levels of structural simplification, irrespective of the season. Forest cover in the surrounding landscape had a significant positive influence on the activity levels of P. kuhlii, and a significant and negative influence on the abundance of P. oleae. Our study demonstrates that structural simplification differentially influences the activity patterns of both insectivorous bats and insect pests within olive groves. Moreover, it suggests that structural simplification may strongly compromise biocontrol services provided by bats on the major olive pest P. oleae.

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&ndash, 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 &ldquo, cul-de-sac&rdquo, and &ldquo, basket traps&rdquo, 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&times, 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&times, 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&times, 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.

Spatial heterogeneity – in terms of topography, and macro- and microclimatic conditions, among others – results in habitat diversity, which in turn may promote species diversity. Thus, the spatial structure (i.e. spatial variance partitioning at different scales and spatial arrangement of drivers of abundance) of the different feeding guilds within food webs may reflect relevant differences in the way populations interact and how these interactions affect ecosystem processes. Our study focuses on the spatial distribution of animals living in the leaf litter layer of beech forests in the National Parks of northern Spain, across sites which differ in precipitation. Using Generalised Linear Mixed Models we estimated the spatial variance components at different scales and for three feeding guilds in leaf litter food webs: saprophagous and microphytophagous mesofauna, saprophagous macrofauna and zoophagous macrofauna. We found that the only consistently significant source of variation for the three feeding guilds was that at the level of “among valleys within Parks”, which, among other potential explanations, could reflect meso-climatic differences among valleys. We also studied which factors may control spatial variation in these food webs through a model selection approach. Controlling for all other relevant factors, we still found strong differences in abundances among National Parks. Also, invertebrates were more abundant in micro-sites located at the base of slopes – where nutrients and water accumulate – than in micro-sites located on the slopes – which, due to surface runoff, are drier and accumulate fewer nutrients. Also, as found in beech forests of Central Europe, limestone sites have higher abundances of fauna than siliceous sites with lower pH. The macro- and micro-scale dependence of these food webs on water availability could have important consequences for the persistence of these forests under global warming.

The analysis of the causes of selection is in essence a problem in ecology Wade and Kalisz 1990 Past evolution determines the genetically determined available phenotypes in populations which affect ecological dynamics in communities, shaping in turn the selective pressures that further model phenotypes. Because an increase in temperature increases metabolic rates and encounter rates, climate change may have profound eco-evolutionary effects, possibly affecting the future persistence and functioning of food webs. We introduce a semi-spatially explicit individual-based model (IBM) framework to study functional eco-evolutionary dynamics in food webs. Each species embedded in the web includes 13 genetically determined and multidimensionally variable traits (the G matrix), 4 of which are flexible physiological and behavioural (personality) traits that respond to temperature. An increase in temperature and stronger correlation among traits leads to stronger trophic cascades but higher stochasticity, with higher probability of extinction for some trophic levels. A combination of the abiotic (temperature) and biotic (predators’ presence/absence) matrix of selective agents (the O matrix) generates differential selection for activation energies for metabolic rates and several instances of correlational selection (selection in one trait changes with the levels of another), suggesting how global warming might favour certain trait combinations. Our results and the future prospects of this IBM approach open new avenues for climate change research.