Population genetics suggests effectiveness of habitat connectivity measures for the European tree frog in Switzerland

摘要

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 contem_porary 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 contempo_rary 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 diffuse. 4. Our results show that the connectivity measures implemented in the Reuss valley facilitated effec_tive 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 move_ment 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 responsi_ble authorities from both river valleys to continue implementing connectivity measures and to create a dense network of breeding sites, as spatial gaps of 8 km are rarely traversed by tree frogs.