Successful habitat connectivity measures for tree frogs
To preserve species and habitats of great conservation value, the Swiss Government and other authorities spend large sums of money on the implementation of connectivity measures. The aim is to enhance the dispersal of individuals and gene flow among remnant populations within fragmented landscapes. These processes are essential for the long-term survival of endangered species as they counteract the negative effects of genetic erosion.
Here we present the main results of an interdisciplinary project in which genetic methods were used to evaluate the effectiveness of connectivity measures implemented for the European tree frog (Hyla arborea). In the project, the spatial genetic structure of remaining tree frog populations was evaluated at the landscape scale, and the influence of several landscape elements on individual movement was studied. In addition, a subsample of populations was tested for fitness differences in a common garden experiment.
The results showed a clearly defined spatial genetic structure of tree frog populations and confirmed individual exchange among breeding sites at distances of up to 4 km. The landscape genetic analysis affirmed that at distances below 2 km, streaming waters like the river Reuss acted as barrier to gene flow whereas surrounding tree frog breeding sites had a positive effect. The common garden experiment suggested that lack of gene flow among breeding sites can lead to negative effects on individual fitness. A functional habitat network for European tree frogs in fragmented landscapes should therefore exhibit a maximum mesh width of 2 km.