Beech cupules as keystone structures for soil fauna

Abstract

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.

Mass–length allometry covaries with ecosystem productivity at a global scale

“…Lower energy storage in the more productive ecosystems, and the suggested faster development in warmer and wetter environments, as well as at higher altitudes and latitudes, may be a sign that energy is processed differently by the soil fauna in different parts of the globe, and in locations of contrasting climates. The latter could affect studies in which it is assumed that mass–length relationships for the different animal groups are invariant, and that estimates coming from different localities and climates can be used indistinctly (e.g., Ehnes et al, ; Melguizo‐Ruiz, Jiménez‐Navarro, & Moya‐Laraño, ). In addition, these findings may have important consequences for the energy equivalence rule (Damuth, ), which states that animal populations in communities use an equal amount of energy regardless of the individual body sizes (in terms of mass), which explains why larger animals have lower abundances and smaller animals have higher abundances.…”

NATURAL ENEMIES OF HERBIVORES MAINTAIN THEIR BIOLOGICAL CONTROL POTENTIAL UNDER FUTURE CO2, TEMPERATURE AND PRECIPITATION PATTERNS

“…While arachnids and insects possessing a waxy cuticle can reduce evaporation (Berridge 2012), soft body organisms (nematodes, isopods, and myriapods) may suffer larger water loss under drought conditions (Sylvain et al 2014). Drought may also prompt arthropod predators to migrate, hide in the soil or build shelters to avoid desiccation (Willmer 1982;Berridge 2012;Melguizo-Ruiz et al 2016), thus reducing their foraging activity.…”

Field exclusion of large soil predators impacts lower trophic levels and decreases leaf‐litter decomposition in dry forests

“…For instance, intermediate levels of fungal grazing by springtails can stimulate fungal growth and promote decomposition, while overgrazing by springtails, in the absence of predators, may lessen fungal populations, resulting in reduced rates of decomposition (Lawrence & Wise, ), with effects being more pronounced in drier soils. Moreover, soil moisture may influence invertebrate activity and abundance, increasing predator–prey encounters as fauna aggregate in water‐rich areas (Melguizo‐Ruiz, Jiménez‐Navarro, & Moya‐Laraño, ; Melguizo‐Ruiz, Verdeny‐Vilalta, Arnedo, & Moya‐Laraño, ; Verdeny‐Vilalta, ; Verdeny‐Vilalta & Moya‐Laraño, ) and predators seek prey as sources of water (McCluney & Sabo, ). Thus, short‐term changes in water availability can alter the direction of trophic cascades.…”