| Abstract |
Background The concepts of environmental niche and hybridization have long been the subjects of both numerous studies and epistemological discussions. Despite attempts for the formation of unambiguous terminology and clear methodology for their joint study, many and difficult issues still remain. Relatively recently, the use of Species Distribution Modelling in the study of hybridization patterns has been suggested in theory, allowing for new approaches in important issues. However, this field has not yet been systematically adressed, so an attempt is made in the current study.
Targets This study aims to methodologically and theoretically contribute in the study of hybridization patterns, focusing on the hybrid systems of the genus Origanum and Phlomis. Specifically, for these two systems we attempt to (1) reveal the spatial patterns of the potenital distribution of the involved entities, (2) conduct a comparative analysis of their niche structure, (3) analyse the hybridization models that fit the two systems and (4) reveal the patterns of Biotic, Abiotic and Mobility constraints that act upon hybrids.
Methodology Initially, the potential distribution of all involved entities was estimated using statistical modelling based on a maximum entropy algorithm and presence data. Consequently, we employed four groups of tests in order to analyse the niche position and breadth of hybrids relative to their parentals, both in Geographical Space and in Environmental Space. Moreover, for the Origanum hybrid system, the same procedure was repeated for the genotypic classes that resulted from genetic analysis of the involved taxa. Finally, absence data were employed in the analysis of Biotic, Abiotic and Mobility constraints of the studied hybrids.
Results The predictive performance of all models was high. The potential distributions of hybrids were found to be broader than their observed distributions; an indication of factors, other than abiotic, affecting the realized hybrid spatial patterns. There was a general tendency of similarity of hybrids and their parental species with regard to niche position, which was also true for genotypic classes of the Origanum hybrid system. Nevertheless, the hybrids were generally characterized by greater niche breadth than their parentals. We also found that none of the hybrid systems could fit reasonably well to the predictions of classic theoretical hybridization models, such as tension zones, bounded hybrid superiority and mosaic zones. Moreover, analysis of Biotic, Abiotic and Mobility restrictions that define absences revealed the spatial complexity of the studied hybrid systems.
Conclusions An emerging pattern is that, based on the current classification of hybrid systems, many of the factors and mechanisms that play an important role in shaping the spatial patterns of hybridization seem to remain in the background. However, the proposed methodology can reveal complex interactions both between the taxa involved in a hybrid system and between the effects of biotic, abiotic and mobility factors, offering an integrated approach for the analysis of hybridization patterns. Application of the proposed methods, apart from providing comparable results, also led to the hypothesis of latent novelty, a theoretical framework that contributes in understanding both niche differentiation of hybrids and their response in changing environments, while also providing general insights in ecosystem diversity.
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