Habitat fragmentation is one of the most important threats to plant species diversity. For different reasons, orchids can be expected to be very susceptible to the consequences of habitat fragmentation. The general objective of this project is to determine viability and extinction risk of fragmented orchid populations by assessing their degree of pollen limitation, genetic structure, demographic rates and average plant fitness. More specific we aim at testing the following hypotheses:Small and isolated orchid populations suffer from genetic erosion and pollen limitation; Reduced genetic diversity negatively affects fitness of orchid species; Pollen limitation in orchid species negatively affects demographic rates, but only when the cost of fruiting is not too high; Past genetic bottlenecks in orchid populations still influences current genetic diversity and fitness; Habitat fragmentation negatively affects pollen and seed flow between orchid populations; The genetic, demographic and fitness response to habitat fragmentation is stronger for a rewarding (nectariferous) orchid species than for a non-rewarding (nectarless) species. To achieve the overall objectives and test the specific hypotheses, we aim at combining an experimental and observational approach, and at applying recently developed, state-of-the-art tools such as integral projection modelling, genetic assignments to infer gene flow, and model-based Bayesian methods to detect the timing and extent of genetic bottlenecks. Our study area are the calcareous grasslands of the Viroin valley