Species' responses along environmental gradients on different spatial scales

The abundance of species on Earth varies greatly - while some occur all over the globe, others can only exist in very distinct regions. Trying to explain the reasoning behind the temporal and spatial variation in the commonness and rarity of species has a long history in ecology and yet, many pieces are still missing to complete the puzzle. This thesis investigates species' responses to changing environmental gradients and asks in how far niche characteristics can be used to predict species' range sizes at different spatial scales. We worked with herbaceous species from semi-natural grasslands as well as deciduous forests, focusing especially on their reactions to abiotic conditions (soil pH, nutrients and light). We could show that the breadth of resources used by species (especially regarding soil pH), as well as their tolerance limits, are reliable predictors for their rarity and commonness across different spatial scales. Furthermore, we believe that niche properties can provide guidelines for conservation decisions, especially concerning the selection of suitable habitats for the reintroduction of species. This is a particularly important task to preserve the world s biodiversity in today s ever changing environments.