1. Governmental authorities in many countries financially support the implementation of habitat
connectivity measures to enhance the exchange of individuals among fragmented populations. The
evaluation of the effectiveness of such measures is crucial for future management directions and can
be accomplished by using genetic methods.
2. We retraced the population history of the European tree frog in two Swiss river valleys (Reuss
and Thur), performed comprehensive population sampling to infer the genetic structure at 11
microsatellite markers, and used first-generation migrant assignment tests to evaluate the contemporary
exchange of individuals.
3. Compared with the Thur valley, the Reuss valley has lost almost double the number of breeding
sites and exhibited a more pronounced genetic grouping. However, similar numbers of contemporary
migrants were detected in both valleys. In the Reuss valley, 81% of the migration events
occurred within the identified genetic groups, whereas in the Thur valley migration patterns were
4. Our results show that the connectivity measures implemented in the Reuss valley facilitated effective
tree frog migration among breeding sites within distances up to 4 km. Nevertheless, the Reuss
valley exhibited high genetic differentiation, which reflected the impact of barriers to tree frog movement
such as the River Reuss. By contrast in the Thur valley, a larger number of breeding sites have
been preserved and high admixture indicated exchange of individuals at distances up to 16 km.
5. Synthesis and applications. We show that genetic methods can substantiate the effectiveness of
connectivity measures taken in conservation management at the landscape scale. We urge responsible
authorities from both river valleys to continue implementing connectivity measures and to
create a dense network of breeding sites, as spatial gaps of 8 kmare rarely traversed by tree frogs.