This method is used to measure the level of genetic differentiation between populations or individuals of the same species. The less differentiation there is, the greater the genetic similarity of populations. If there is little or no exchange between isolated populations over a long time period, gene flow is low and therefore the level of genetic differentiation increases. This method is well suited to measure the exchange among populations over longer time periods, because genetic differentiation is a long-term process.
Example: the dispersal of large marsh grasshoppers in the Oberaargau region
The large marsh grasshopper (Stethophyma grossum) lives in wetland areas, including wet grassland and riverbanks. It is a good indicator of intact wetlands and is an endangered species in Switzerland due to widespread drainage of wetland areas in recent decades.
WSL investigated the impact of landscape structure on the genetic differentiation and dispersal of the large marsh grasshopper in the Oberaargau region. Here, the species is found in wetland meadows along ditches, streams and the rivers Rot, Langete and Önz. WSL researchers recorded 37 populations and determined their genetic differentiation. Populations located close to each other in the same river valley were genetically similar and more closely related than populations in different river valleys. The study shows that large marsh grasshoppers mainly disperse within – rather than between – valleys.
In this way, genetic methods increase our basic knowledge about the dispersal of animals that are difficult to observe. This information is important for planning and implementing appropriate measures to promote endangered species.