The focus of my PhD research is to understand how habitat heterogeneity influences species composition and biodiversity of grassland communities. Traditionally, it is believed that an increase in habitat heterogeneity has a positive effect on biodiversity, as more species with different ecological needs will find a suitable habitat. However, some empirical data suggest that the effect of heterogeneity on biodiversity might as well be negative, neutral or unimodal. According to the Area-heterogeneity trade-off (AHTO) proposed by Kadmon and Allouche (2012) environmental heterogeneity has two opposite effects on species richness. On one hand it increases opportunities for niche partitioning, but at the same time it reduces the amount of suitable area available for each species thereby increasing the probability of stochastic extinction. To test the predictions of the AHTO model I set up a long term microcosm experiment simulating different combinations of habitat types and land use, in which species abundance data and biomass are monitored across consecutive years.