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 activities through their decaying fruit husks, hence acting as ecosystem engineers., This work has been funded by Spanish Ministry of Science and Innovation grant CGL2010-18602 and CGL2015-66192-R to JML, the European Regional Development Fund and FPI fellowship (BES-2011-043505) to NMR. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript., Peer reviewed

© The Author(s)., 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, This work was funded by grants CGL2010-18602 and CGL2015-66192-R from the Spanish Ministerio de Economía y Competitividad (European funds FEDER), 020/2008 from Spanish Organismo Autónomo de Parques Nacionales, and P12-RNM-1521 from Junta de Andalucía (European funds FEDER) and the FPI fellowship (BES-2011-043505) to N.M.R. D. Ruiz-Lupión is enjoying a FPU (FPU13/04933) scholarship from the Spanish Ministerio de Educacion, Cultura y Deporte., Peer reviewed

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 < 1,250 mm and four wet 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.

Abstract
Aim
It is still debated whether allometry, the relationship between body size and body parts, entails merely an evolutionary constraint or can itself evolve. Recently, a hypothesis has been proposed that states that static allometry (allometry measured across individuals at the same developmental stage) can evolve from differences in the developmental pathways between pairs of traits under different nutritional environments. A macroecological prediction stemming from this hypothesis is that allometric coefficients (scaling and allometric factors) should covary with ecosystem productivity. Here, we tested this prediction using a worldwide database of mass¿length allometric equations.

Location
Worldwide, data distributed across the entire globe.

Time period
1967¿2017.

Major taxa studied
Soil arthropods.

Methods
We fitted general linear models with the allometric coefficients (the scaling a and allometric b factors) as the dependent variables. The target independent variable was the normalized difference vegetation index, as a proxy of ecosystem productivity. Longitude, absolute latitude and altitude, as well as mean annual temperature and mean annual precipitation were included as both covariates and additional variables of interest. We also included body bauplan (obtained from geometric morphometrics), taxonomic affiliation (a proxy of phylogenetic relationships) and the reciprocal allometric coefficient as covariates in the model.

Results
We found a strong negative association between both allometric factors and the productivity of the ecosystems, and the effect for the allometric factor b was stronger at lower trophic levels. We also detected strikingly similar effects of geographic and climatic predictors on both allometric factors, suggesting the occurrence of similar selective regimes.

Main conclusions
The fact that productivity, geography and climate affect the value of mass¿length allometric coefficients has important consequences not only to understand the evolution of allometries, but also for how energy is processed in soil ecosystems across the globe., Ministerio de Educación, Cultura y Deporte. Grant Number: FPU13/04933
Consejo Superior de Investigaciones Científicas. Grant Numbers: CGL2014‐61314‐EXP , CGL2015‐66192‐R
Consejería de Economía, Innovación, Ciencia y Empleo, Junta de Andalucía. Grant Number: P12‐RNM‐1521

High-throughput DNA methods hold great promise for phylogenetic analysis of lineages that are difficult to study with conventional molecular and morphological approaches. The mites (Acari), and in particular the highly diverse soil-dwelling lineages, are among the least known branches of the metazoan Tree-of-Life. We extracted numerous minute mites from soils in an area of mixed forest and grassland in southern Iberia. Selected specimens representing the full morphological diversity were shotgun sequenced in bulk, followed by genome assembly of short reads from the mixture, which produced >100 mitochondrial genomes representing diverse acarine lineages. Phylogenetic analyses in combination with taxonomically limited mitogenomes available publicly resulted in plausible trees defining basal relationships of the Acari. Several critical nodes were supported by ancestral-state reconstructions of mitochondrial gene rearrangements. Molecular calibration placed the minimum age for the common ancestor of the superorder Acariformes, which includes most soil-dwelling mites, to the Cambrian–Ordovician (likely within 455–552 Ma), whereas the origin of the superorder Parasitiformes was placed later in the Carboniferous-Permian. Most family-level taxa within the Acariformes were dated to the Jurassic and Triassic. The ancient origin of Acariformes and the early diversification of major extant lineages linked to the soil are consistent with a pioneering role for mites in building the earliest terrestrial ecosystems., This research was funded by the NHM Biodiversity Initiative and the CGL2015-66192-R and CGL2015-74178-JIN projects. PA was supported by the Royal Society UK (Newton International Program) and the Spanish Ministry of Economy and Competitiveness (Juan de la Cierva Formación); BL by the NHM Biodiversity Initiative and French Labex Agro-CeMEB-NUMEV, Peer reviewed

The relative body size at which predators are willing to attack prey, a key trait for predator-prey interactions, is usually considered invariant. However, this ratio can vary widely among individuals or populations. Identifying the range and origin of such variation is key to understanding the strength and constraints on selection in both predators and prey. Still, these sources of variation remain largely unknown. We filled this gap by measuring the genetic, maternal and environmental variation of the maximum prey-to-predator size ratio (PPSRmax) in juveniles of the wolf spider Lycosa fasciiventris using a paternal half-sib split-brood design, in which each male was paired with two females and the offspring reared in two food environments: poor and rich. Each juvenile spider was then sequentially offered crickets of decreasing size and the maximum prey size killed was determined. We also measured body size and body condition of spiders upon emergence and just before the trial. We found low, but significant heritability (h2 = 0.069) and dominance and common environmental variance (d2 + 4c2 = 0.056). PPSRmax was also partially explained by body condition (during trial) but there was no effect of the rearing food environment. Finally, a maternal correlation between body size early in life and PPSRmax indicated that offspring born larger were less predisposed to feed on larger prey later in life. Therefore, PPSRmax, a central trait in ecosystems, can vary widely and this variation is due to different sources, with important consequences for changes in this trait in the short and long terms., This study was supported by a PhD grant (PD/BD/106059/2015) attributed to JFH by the Portuguese Science and Technology foundation (FCT), by the grant P12-RMN-1521 from the Andalusian government and by the grant CGL2015-66192-R from the Spanish Ministry of Economy and Competitiveness, both partially funded by the European Regional Development Found, both attributed to Jordi Moya-Laraño and to the FPU scholarship (FPU13/04933) from the Spanish Ministerio de Educacion, Cultura y Deporte to Dolores Ruiz-Lupión., Peer reviewed

Under ongoing climate change, the success of biological pest control might be at risk if in the process of massrearing, the populations of commercial biological control agents lose genetic variability in traits that allow adaptation linked to satisfactory pest control in future crop conditions. The isofemale line technique was used to estimate the broadsense heritability (H²) in 22 morphological, life history, physiological, and behavioral quantitative traits from two populations of the species Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae): one commercial, acquired from a company; and the other wild, obtained by the authors from field collections in the region where this species is native. None of the traits estimated in the commercial population held genetic variance (H²~0), whereas the H² of 5 traits related to development time and morphology were significant in the wild population. Analyzing together the isolines of both populations allowed increasing the number of significant H² estimates to 12, which included physiological traits such as desiccation and starvation resistance. Assuming similar genetic drift in both populations, the fact that heritability estimates in the commercial population were estimated to be almost null indicated that this population might have undergone selection leading to a decrease in genetic variability. Unintentional adaptations to long-term captive conditions can have drastic effects on the performance of BCAs. Low genetic variability in commercial populations may limit their within-generation persistence in the field, as well as their potential for between-generation rapid adaptation in response to environmental changes, ultimately jeopardizing pest control., This work was executed thanks to Grant CGL2015-66192-R funded by MCIN/AEl/10.13039/501100011033 and the “ERDF A way of making Europe”, Grant PID2019-103863RB-I00, funded by MCIN/AEl/10.13039/501100011033, Grant BES-2016-077723, funded by MCIN/AEI/ 10.13039/501100011033 and the “ESF Investing
in your future”, and Grant TED2021-129653B-I00, funded by MCIN/AEl/10.13039/501100011033 and the “European Union NextGenerationEU/PRTR”, Peer reviewed

If we are to sustainably provide food to a rapidly growing human population, biological pest control (BPC) should integrate food web theory and evolution. This will account for the impacts of climate warming on the complex community settings of agroecosystems. We review recent studies looking for top-down augmentative pest control being hampered/promoted by biotic (community contexts) and/or abiotic (climate) drivers. Most studies found either positive or neutral effects on BPC. However, most ignored potential evolutionary responses occurring in the environments under study. We propose engineering food webs by engaging in a continuous feedback between ecological and evolutionary data, and individual-based modelling of agroecosystems. This should speed up the procurement of strains of efficient natural enemies better adapted to warming., The authors of this work were supported by funds from the Spanish
Ministry of Science, Innovation and Universities (refs: CGL2015-66192-R,
PID2019-103863RB-I00), and the European Union (refs: RIA-773902-2,
APCIN2016-00027), Peer reviewed