Space and specieson the relationships between spatial processes and diversity patterns of trees

Laburpena

Although the world is unavoidably spatial, and each organism is a discrete entity that exists and interacts only within its inmediate neighborhood, these realities long have been ignored by most ecologists because they can greatly complicate field research and modeling. However, several lines of inquiry have highlighted the potentially critical roles of space and led to growing interest in Spatial Ecology. In the present thesis we focus on the study of processes characterized by a certain spatial structure that may directly affect the diversity patterns observed in nature. In the first chapter, we have explored a spatial process which showed a temporal structure as well (i.e. historical pattern of glacial retreat in response to post-Pleistocene global warming). Similarly, habitat loss and fragmentation influences the observed patterns of presence/absence, richness, abundance and extinction of species, and thus this process has been a main milestone of this thesis. Last, we have applied spatial analysis techniques to investigate the validity of the so-called Species Distribution Models (SDMs) to explain the spatial structure of species within their distribution ranges; this information has been used to deduce spatial processes underlying such patterns. The study of these spatial processes has been conducted for tree species. This decision has been made following two criteria: (1) to maintain coherence among the different chapters of this thesis with respect to the biological group subject of analysis, and (2) because of the higher data availability and quality on presence/absence and richness patterns for tree species. To conduct this thesis we have used empirical data from different datasets, and used different methods and techniques that range from Geographic Information Systems to mathematical and simulation models and spatial structure analyses widely used in Spatial Ecology.