Spatial structure of biodiversity: local and regional patterns in an insular ecosystem

Zusammenfassung

Understanding the origin and structure of biodiversity, along with the processes that underpin both, provides essential information for conservation. In priority areas such as oceanic islands, this information may be particularly important for the preservation of their singular, and at the same time threatened, biodiversity. Here, we present an integrative approach, combining standardised single-locus (mitochondrial) community sampling with high resolution genomic data (ddRAD-seq), as a effective strategy to analyse beetle community assembly within an insular ecosystem across different spatial scales, from regional (i.e. archipelago) to local (i.e. small scale within island). We focus on the study of “non-adaptive” mechanisms potentially promoting neutral speciation, such as reductions in gene flow facilitated by (i) species dispersal limitation, (ii) geology, (iii) topography, (iv) Quaternary climate variation, and (v) niche conservatism. Within this thesis it is demonstrated that dispersal limitation is an important driver promoting diversification within the Canary Islands for a significant part of the beetle fauna. At the archipelago scale, this is mainly due to isolation by resistance induced by oceanic barriers. Within islands, the interplay between topography and climate plays a key role in the process of diversification for species with limited dispersal ability and climate tolerance, generating patterns of isolation by niche conservatism at small spatial scales. This pattern, along with signatures of admixture at intermediate sites and historic demographic analysis, also reveals a repeated dynamic of isolation and secondary contact induced by Quaternary climate cycles across a spatially limited environmental discontinuity, pointing to the downward shift of the Macaronesian laurel forests linked to climatic warming. In addition to the underlying importance of climate, history and spatial scale for the beetle community assembly in the oceanic islands, this study points to flightless and hydrophilic species of beetles, such as Acalles globulipennis, as potential indicators of how past climate change has influenced the distribution of habitat, potentially offering the possibility to predict future responses to global warming.