Abstract
Biodiversity is not randomly distributed in space and understanding of diversity patterns can shed light on the factors and processes that shape it. The aim of this thesis is to detect and study spatial diversity patterns. Using an alternative sampling method, I estimated the area that contains a specified number of species (minA) and the species-area relationship (SAR) resulting from minA (Chapter 1). The spatial patterns of different diversity dimensions (α-, β- and γ-diversity) vary with the scale of observation (Chapter 2). The scale of observation depends on the taxonomic group’s characteristics, while differences between the human and taxonomic group’s scale of observation could add noise to the observed patterns. The sampling design is defined by the researcher and affects the spatial patterns. Contrariwise, the sample size and shape in the minA approach are defined by the species presence data eliminating the scale effect. The minA is defined as the minimum convex hull having a ...
Biodiversity is not randomly distributed in space and understanding of diversity patterns can shed light on the factors and processes that shape it. The aim of this thesis is to detect and study spatial diversity patterns. Using an alternative sampling method, I estimated the area that contains a specified number of species (minA) and the species-area relationship (SAR) resulting from minA (Chapter 1). The spatial patterns of different diversity dimensions (α-, β- and γ-diversity) vary with the scale of observation (Chapter 2). The scale of observation depends on the taxonomic group’s characteristics, while differences between the human and taxonomic group’s scale of observation could add noise to the observed patterns. The sampling design is defined by the researcher and affects the spatial patterns. Contrariwise, the sample size and shape in the minA approach are defined by the species presence data eliminating the scale effect. The minA is defined as the minimum convex hull having as vertices the presence points of S species closer to the sampling’s starting point. The minA has a negative relationship with abundance equitability and increases with species spatial aggregation. The minA patterns for the African reptiles (Sauria, Serpentes, Amphisbaenia και Testudines) vary among taxonomic groups and with the requested number of species, are consistent with regions of high species richness, but cannot identify regions with medium diversity. The intercept and slope of SAR, the increase of species number with area, are considered indices of α- and β-diversity respectively, but depend on the sampling design, thus complicating the identification of underlying processes (Chapter 3). The species-minimum area relationship (minSAR) is introduced that results from minA method. The minSAR slope increases with abundance equitability and species random placement. In African reptiles, the slope exhibits the pattern Sauria>Serpentes>Amphisbaenia>Testudines and the intercept Testudines>Serpentes>Amphisbaenia >Sauria. The patterns of α- and β-diversity differ among taxonomic groups suggesting that minSAR can decipher the underlying mechanisms. The diversity patterns are shaped by species distributions and their overlap, which are defined by abiotic and biotic factors like biotic interactions, whose effect can be detected even in large scales (Chapter 4). The effect of prey species number was examined on the distribution of a generalist predator, the grass snake (Natrix natrix). Two species distribution models were applied with predictors: abiotic factors (abiotic) and the addition of prey species number (biotic) and taking into account dispersal ability. The two models had similar performance, with temperature and isothermality being important factors in both. Yet, the prey species number was the most important variable in the biotic model. The dispersal ability will define the future distribution of grass snake, either by moving northwards or significant reduction if the species cannot disperse. The species distribution in the south part of its range will not change according to the biotic model underlining the role of biotic interactions as potential response mechanism of biodiversity to climate change.
show more