Beyond beaches and environmental filtering: functional diversity patterns of microscopic animals across different habitats
Overall, regardless of the processes involved in adaptations to different hydrodynamics, for proseriates from reflective beaches in the Western Mediterranean Sea, we demonstrated that the rough hydrodynamic conditions in the swash level shape diversity patterns. Wave incidence selects for species bearing adaptations to cope with turbulence, leading to the presence of highly specialized communities in these areas, compared to those in the deeper shoaling and subtidal levels.
Our results add more support to previous analyses, which highlighted that environment might act affecting the distribution of microscopic animals in a comparable way than larger species. Distribution of microscopic animals might appear either uniform or random, simply as a consequence of the smaller scale, which brings a higher uncertainty associated with measurements and morphological interpretation at the. As previously suggested, microscopic size may generate uncertainty in a macroscopic observer, on both the definition of traits and the definition of niche even if the environment did select. Here again, a functional ecology-based study, in which we selected traits with a clear functional meaning related to habitat occupation, has revealed that the distribution of species within the beach is not random but clearly response to the turbulence gradient of the beach. Similar processes of ecological filtering in response to has been observed in meiofaunal groups dwelling in hard substrate or marine algae and phanerogams exposed to different degrees of turbulence, such as marine mites (Riesgo et al., 2010; Martínez, García-Gómez, et al., 2021). In freshwater, a certain degree of trait selection has been demonstrated in the nematode communities dwelling in sediments between intermittent and permanent streams (Majdi et al., 2020), as well as in the communities associated to mosses (Kreuzinger-Janik et al., 2021). However, evidence for ecological selection of traits is also present in other groups, including free-living (Jaturapruek et al. 2021) and epibiont bdelloid rotifers (Fontaneto & Ambrosini, 2010), as well as Cycliophora (Baker et al., 2007). In those, cases, though, the effect of the environment was comparatively weak, and could only be seen as differences in the relative abundance of the traits. In the swash zone of sandy beach, the effect is stronger and could be quantified even if the relative abundance of different species could not be considered. Those studies collectively emphasize the need of moving from a merely taxonomical towards a functional view of ecological studies of microscopic organisms (Violle et al. 2014). Further steps in this direction will warrant a better mechanistic understanding of their habitat and distribution patterns.
All this evidence collectively suggests that, indeed, environment does select for the presence of different species in meiofauna, suggesting that ecological processes might play and important role in the evolution of new species, also amongst microscopic animals (Nosil, 2012).
Conflict of interest statement. Authors declare that they have no competing interests.