Colonization, niche and coexistence across spatial scales in Mediterranean bryophytes

Abstract

The main objective of this thesis is to study the factors determining the coexistence of species across spatial scales using Mediterranean bryophytes, exploring their colonization, niche, and coexistence. The specific objectives will first address establishment success, early development, and characterization of bryophyte species' diaspores by culturing experimental communities of Mediterranean mosses in growth chambers. Subsequently, biotic interactions and co-occurrences at different spatial scales along environmental gradients will be evaluated, using specific indices and characterizing bioclimatic niches for those and other Mediterranean bryophyte species. This assessment is conducted on the aforementioned cultures and co-occurrence records at different scales, in combination with environmental climate variables, to integrate the information across scales. We also include information on the taxonomic proximity of the analyzed bryophyte species as an indicator of their phylogenetic and functional similarities. The analyses of the cultures provided us with information about their establishment and early development as diaspores, the central colonization phase in bryophytes. In addition, we described previously unexplored traits concerning the size and shape of diasporas, which could have significant implications for the processes of dispersal and establishment. Moreover, we found insights of the role of the environmental gradients in modulating the spatial associations of species. Throughout the process, we were able to integrate and discuss the relevance of the coexistence principle, the Stress Gradient Hypothesis (SGH), the Bryophyte Favourability Gradient Hypothesis (FGH), and coexistence mechanisms that affects bryophyte’s spatial associations. Notably, positive associations are common in bryophytes, and despite the high frequency of interactions, associations between bryophytes are mainly regulated by abiotic factors at all scales. Their explanation is complex and may be related to a combination of the FGH and biological filters, which may also overlap with interpretations of the SGH. Furthermore, taxonomic proximity is a good predictor of local-scale co-occurrence.