Species-specific results
For the damselfly C. mercuriale, we found agriculture to be the main migration habitat. However, a detailed analysis separating different spatial scales of migration showed that frequently occurring short-distance migration (< 3 km) followed streams and ditches, i.e. the reproductive habitat, and that rare long-distance migration also crossed agricultural land. Elevation change (e.g. hill ridges), Euclidian long-distance and forest hindered gene flow and migration, while open agricultural land enhanced gene flow. Occur-rences of C. mercuriale in our study area form connected networks of populations if they are within the same ditch system and if there are no major forests or elevation obstacles separating the occurrences.
For the wetland grasshopper S. grossum, we also found the reproductive habitat to be the optimal tion habitat for short-distance migration. For long-distance migration, however, no distinct preferred migra-tion habitat could be identified. Furthermore, we found that network topology could be used to define the spatial scale threshold up to which landscape elements affect gene flow. For short-distance migration, the proportion of water bodies and roads facilitated gene flow, whereas forests, settlements and path length acted as barriers. Population structure of this wetland species mainly coincided with the flood plains in the valley bottoms.
For the three grassland grasshoppers, a first analysis did not find any effect of ECAs on their distribution and genetic patterns, which might be a result of high connectivity and massive gene flow in the studied landscape of the Oberaargau. A series of much more detailed analyses will be necessary to prove that this result really holds true (STRUCTURE, partial Mantel tests based on habitat suitability models and species-specific LCTA analyses). However, note that the above result means that for three common grasshoppers the agricultural landscape of the Swiss lowlands still provides connected habitat: a positive message.
Methodological results
Least-cost transect analysis (LCTA) proved to be a useful approach to determine the most probable migration habitat of focal species. The method outperforms existing methods in a statistical way and produces results that are easier to interprete than those of traditional landscape genetic methods.
The simulation study is still in development. Preliminary results show that genetic patterns are mainly the result of stochastic processes and the level of fragmentation and type of migration are of much less importance. If this result is substantiated in further analyses, it would imply that that regional differences between genetic patterns may not be the result of differences in landscape composition and configuration, but mainly be the result of random gene flow events.
Mark-recapture studies proved to be useful for the detection of frequently occurring short-distance migra-tion, but not for rare long-distance migration events. However, these rare events are of particular
impor-tance for maintaining connectivity in highly fragmented landscapes and can be characterised by using genetic methods.
Genetic measures are hence suitable to measure gene flow, especially over large distances. Our results also indicated that measures reflecting recent gene flow (e.g. from assignment tests) might be more ap-propriate for landscape genetic studies, especially if contemporary landscape configurations is used.
Population network topology can be used in landscape genetic analyses to assess the relevant spatial scale up to which landscape should affect gene flow. This requires, however, an almost complete sam-pling of all populations in a study area. In addition, mapping the reproductive habitat of a study species based on information from the literature can be used as a simple and effective alternative to habitat suit-ability analysis.
General conclusions
Our studies suggest to differentiate between the reproductive and migration habitat of species in future landscape genetic studies.
We also showed that short- and long-distance migration may be directed through different migration habitats. For two study species, we found that only short-distance migration used the reproductive habitat as preferred migration habitat.
The threshold distance separating short- and long-distance migration can be explained by the spatial configuration of populations, i. e. with network topology.
The newly developed method of least-cost transect analysis LCTA provided a powerful landscape genetic tool to analyse migration habitats and detect landscape effects on migration and gene flow, which is important knowledge for the conservation management of connectivity.
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