Soil Layers Matter: Vertical Stratification of Root-Associated Fungal Assemblages in Temperate Forests Reveals Differences in Habitat Colonization

Ectomycorrhizal and saprotrophic fungi play pivotal roles in ecosystem functioning. Here, we studied the vertical differentiation of root-associated fungi (RAF) in temperate forests. We analysed RAF assemblages in the organic and mineral soil from 150 experimental forest plots across three biogeographic regions spanning a distance of about 800 km. Saprotrophic RAF showed the highest richness in organic and symbiotrophic RAF in mineral soil. Symbiotrophic RAF exhibited higher relative abundances than saprotrophic fungi in both soil layers. Beta-diversity of RAF was mainly due to turnover between organic and mineral soil and showed regional differences for symbiotrophic and saprotrophic fungi. Regional differences were also found for different phylogenetic levels, i.e., fungal orders and indicator species in the organic and mineral soil, supporting that habitat conditions strongly influence differentiation of RAF assemblages. Important exceptions were fungal orders that occurred irrespective of the habitat conditions in distinct soil layers across the biogeographic gradient: Russulales and Cantharellales (ectomycorrhizal fungi) were enriched in RAF assemblages in mineral soil, whereas saprotrophic Polyporales and Sordariales and ectomycorrhizal Boletales were enriched in RAF assemblages in the organic layer. These results underpin a phylogenetic signature for niche partitioning at the rank of fungal orders and suggest that RAF assembly entails two strategies encompassing flexible and territorial habitat colonization by different fungal taxa.

Plasticity To Environmental Conditions And Substrate Colonization Mediates The Invasion of Dreissenid False Mussels In Brackish Systems

False mussels are recognized as the brackish water equivalent of zebra mussels, although the abiotic and habitat conditions that mediate these invaders’ success are barely known. In this context, we aimed to evaluate the native and non-native geographical distribution of Mytilopsis species worldwide and assess biological traits, environmental condition, and habitat associated with false mussels in native and invaded systems. Our hypothesis is that Mytilopsis invasion is driven by species plasticity to environmental conditions and substrate use in brackish systems, where the colonization of non-native populations is favored by great availability of artificial substrates and tolerance to wide ranges of environmental conditions. Besides, this study provides the occurrence range and distribution patterns of Mytilopsis species within their introduced and native areas and tracks the spread of introduced populations worldwide. Considering the five species evaluated, M. leucophaeata and M. sallei are the most widespread, while M. adamsi, M. trautwineana, and M. africana showed more restricted geographic distribution. In the last decades, M. leucophaeata and M. sallei consolidated and expanded their distributions. Environmental conditions were significantly different between native and non-native areas, where Mytilopsis populations presented significantly higher densities. Non-native populations exhibited remarkable plasticity concerning habitat colonization that was more frequent on artificial substrata. Mytilopsis populations presented significant differences on their biological traits, habitat environmental conditions, and substrate use between native and non-native areas. These species seem to adapt to the conditions of invaded systems, changing their preferences, which reflects plasticity and suggests a potential shift of their realized niches.

Bryozoan diversity on a whale bone: an uncommon substrate from the continental shelf off NW Spain

Carcasses and bones of whales are interesting yet poorly understood habitats for invertebrates and microbial communities. Nevertheless, bryozoans have never before been reported in this particular habitat at the present day. Here, we present the first study on a bryozoan community colonizing a whale bone from the continental shelf off NW Spain at 128 m depth. Thirty-three species of bryozoans were identified, representing 50% of the known bryozoan diversity from this area and depth range. Despite this high biodiversity, no potential whale-fall specialists were detected: all the species are already known in the area, with several being more frequent in shallower or deeper waters. Our results support the hypothesis that the number of specialist taxa on whale-fall habitats decreases drastically on whale remains at depths of less than 260 m. These results also support the theory that whale-falls can serve as intermediate habitats where no other suitable substrate is present, facilitating habitat colonization.

Naturally-primed life strategy plasticity of dimorphic Aethionema arabicum facilitates optimal habitat colonization

Plasticity in plant dispersal traits can maximise the ability of a plant species to survive in stressful environments during colonization. Aethionema arabicum (Brassicaceae) is a dimorphic annual species that is hypothesized to survive stressful conditions during colonization due to adaptive plasticity in life-phase (vegetative vs sexual) and fruit morph (dehiscent [DEH] vs indehiscent fruits [IND]). We tested for adaptive plasticity in life-phase and fruit morphs along laboratory environmental stress gradients found in the natural habitats of Ae. arabicum. We considered optimal environmental conditions (750–2000 m above sea level) to be those that resulted in the following fitness parameters: higher biomass and a higher total number of fruits compared to stressful habitats. We found evidence of plasticity in life-phase and fruit-morph along a stressful environmental gradient. High hydrothermal stress proportionally increased the number of dehiscent morphs and non-dormant seeds germinating in autumn. This offsets natural phenology towards dry and cold winter (less hydrothermal stress), yielding fewer fruits that dehisce in the next generation. We conclude that the plastic responses of Ae. arabicum to natural stress gradients constitute a strategy of long-term adaptive benefits and favouring potential pathways of colonisation of the optimal habitat.

Predator diversity reduces habitat colonization by mosquitoes and midges

Changes in predator diversity via extinction and invasion are increasingly widespread and can have important ecological and socio-economic consequences. Anticipating and managing these consequences requires understanding how predators shape ecological communities. Previous predator biodiversity research has focused on post-colonization processes. However, predators can also shape communities by altering patterns of prey habitat selection during colonization. The sensitivity of this non-consumptive top down mechanism to changes in predator diversity is largely unexamined. To address this gap, we examined patterns of dipteran oviposition habitat selection in experimental aquatic habitats in response to varied predator species richness while holding predator abundance constant. Caged predators were used in order to disentangle behavioural oviposition responses to predator cues from potential post-oviposition consumption of eggs and larvae. We hypothesized that because increases in predator richness often result in greater prey mortality than would be predicted from independent effects of predators, prey should avoid predator-rich habitats during colonization. Consistent with this hypothesis, predator-rich habitats received 48% fewer dipteran eggs than predicted, including 60% fewer mosquito eggs and 38% fewer midge eggs. Our findings highlight the potentially important links between predator biodiversity, prey habitat selection and the ecosystem service of pest regulation.