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.