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Aim To assess the relative relevance of dispersal limitation and species sorting as drivers of spatial turnover between spider faunas of European territories. Location Continental Europe. Time period Present. Major taxa studied Spiders (Order Araneae). Methods We analysed how distance-decay patterns differ between northern and southern Europe (broadly, territories covered vs. not covered by ice sheets during the last glacial maximum, respectively) in 15 spider families, using standardized distances to allow a direct comparison between parameters (i.e. slope and intercept) of climatic and spatial distance-decay models. Thus, we assessed North–South differences in parameters of spatial and, independently, climatic distance-decay models, and whether those differences are explained by family-specific traits related to dispersal ability. Results Climatic and spatial distance-decay patterns are very similar in northern Europe, where climatic and spatial distances are highly correlated. In contrast, slopes are steeper in spatial than in climatic distance-decay curves in southern Europe, where climatic and spatial distances are decoupled. Moreover, family traits related to dispersal ability explained the North–South difference in spatial distance-decay slopes, as well as the amount of nestedness-resultant dissimilarity between southern and northern spider faunas. Main conclusions Our results suggest that differences in beta diversity patterns between northern and southern Europe reflect the strength of dispersal limitation in spiders, which varies across families and leads to different degrees of disequilibrium with current climatic conditions depending on the taxon. Moreover, in the South of Europe, where spatial and climatic distances are uncorrelated, spatial distance-decay models are steeper and have larger explanatory power than climatic distance-decay models, which suggests that dispersal limitation is the main factor shaping current beta diversity patterns of Europea

Understanding the factors affecting the spatial structure of biodiversity at various levels of biological organization is one of the main goals for ecologist. This thesis aims to develop new methodologies to study the mechanisms driving the spatial distribution of biological diversity as inferred from biogeographical and macroecological patterns. It explores the usefulness of a sigmoidal function to fit the distance-decay pattern and how its shape change with the species distribution size, a test statistic for parameters comparison, the application of these methods to study current large-scale diversity pattern of European spiders and the extension of these methods to study the genetic-spatial distance relationship, using endemic species of Iberian leaf beetles as case-study.

Aim: (i) To assess the dependence between the form of the decrease in biological similarity with distance (distance-decay) and species range size and (ii) to introduce the use of a sigmoidal model, the Gompertz function, as a flexible alternative able to fit distance-decay models under a wide variety of species range sizes. Location: Applicable worldwide. Methods: We computed distance-decay curves from simulated communities to assess how the species range sizes shape the functional form of distance-decay patterns (i.e. negative exponential, power-law or sigmoidal [Gompertz] relationships). Simulations were performed using different sample sizes and species detection probabilities. We also used distribution data of South American mammals to explore the relationship between species range size and the distance-decay form in an empirical dataset. Results: Our simulations showed that the power-law is the best supported model when range sizes tend to be small. An increase in range sizes leads to a negative expo- nential relationship, taking the shape of a sigmoidal (Gompertz) relationship with the largest range size values. Similar results have been found in the distance-decay pat- tern of South American mammals. Remarkably, the Gompertz function fits the data reasonably well in all scenarios. Main conclusions: The functional form of distance-decay patterns depends on a key biogeographical attribute: species range size. This dependence makes it an interest- ing tool to detect biodiversity threats associated with species range expansion, such as the biotic homogenization of faunas. The Gompertz function is the mathemati- cal model that best accommodates different frequency distributions of species range size and, thus, allows cross-taxa comparison of this biogeographical and ecological pattern.

Modelling how community similarity decays with spatial distance is a key tool for the study of the processes behind community variation (beta diversity). Distance-decay models are computed from pairwise metrics (i.e. community similarity and spatial distance between localities) and hence suffer from pairwise dependence in the data, precluding the use of standard significance tests. Besides, distance-decay patterns are inherently nonlinear because similarity is bounded between 1 and 0. However, the only standard method to assess model significance under pairwise dependency is the Mantel test, which considers a linear model. To allow the use of nonlinear models in the assessment of distance-decay patterns, we introduce here a nonlinear significance test combining a pseudo-R2 statistic with either permutations or block-site resampling with replacement