From local adaptation to range sizes:Ecological and evolutionary consequences of dispersal

Why some species occupy almost all of the Earth’s terrestrial (e.g. barn owl) or marine (e.g. moon fishes) systems, whereas others are only found in single freshwater springs (like the devils hole pupfish) or on small, isolated islands?. What is impeding species to occupy all of the Earth?. Is it that species cannot reach all places because of reduced dispersal abilities? Or is it that geometric constraints and habitat availability plays an important role on how far species can go? Is it that species are adapted to certain abiotic conditions (e.g. salinity, temperature, etc) and they are unable to adapt to habitats where conditions are different? Or is it that they cannot successfully colonize habitats in which competitor species are already present? Is it that just given enough time all species will be able to occupy all places, thus older species are more widespread than younger ones?Ultimately, only a few ecological processes should be important in determining a species’ range size: speciation (creation/division of ranges) dispersal to a new habitat (expansion of the range), successful colonization of that habitat (successful dispersal) and (avoidance of) local extinctions. Among these processes, dispersal has a central role as it is important for population’ persistence in suboptimal habitats, by providing demographic rescue to populations that otherwise would go extinct. Furthermore, dispersal also promotes gene flow, bringing the genetic variability necessary for adaptation, which is important for successful colonization and ultimately range expansion. In this thesis, using a wide variety of approaches and model systems to study how these various mechanisms can act together to eventually determine range sizes