Das Birkhuhn (Tetrao tetrix), einst typischer Bewohner von Moor- und Heidelandschaften, lebt in Deutschland außerhalb der Alpen nur noch in kleinen isolierten Vorkommen. Aufforstungen von Heideflächen und die Entwässerung und Kultivierung von Mooren reduzierten seinen Bestand. Heute steht das Birkhuhn als vom Aussterben bedrohte Art auf der Roten Liste der Brutvögel Deutschlands. Allein in Niedersachsen, wo außerhalb der Alpen noch der größte Birkhuhnbestand lebt, sank die Zahl der Tiere innerhalb der letzten 30 Jahre von rund 4.000 auf heute 200. Das Projekt untersucht die für den Artenschutz zentrale Frage, wie sich die voneinander isolierten Populationen in Deutschland an Veränderungen ihrer Lebensräume anpassen. Daraus sollen dann konkrete Empfehlungen für den Schutz des Birkhuhns abgeleitet werden.
Background Open cast lignite mines, sand pits and military training areas represent human-made, secondary habitats for specialized xerothermophilous and psammophilous species. Rare species, including the earwig Labidura riparia, are found in high population densities in such sites. However, it is unknown from which sources colonisation took place and how genetic variation compares to that of ancient populations on natural sites.
Methods Using nine microsatellite markers, we analysed genetic variation and population structure of L. riparia in 21 populations in NE Germany both from secondary habitats such as lignite-mining sites, military training areas and a potassium mining heap, and rare primary habitats, such as coastal and inland dunes.
Results Genetic variation was higher in populations from post-mining sites and former military training areas than in populations from coastal or inland dune sites. Overall population differentiation was substantial (FST = 0.08; F'st = 0.253), with stronger differentiation among primary (FST = 0.196; F'st = 0.473) than among secondary habitats (FST = 0.043; F'st = 0.147). Differentiation followed a pattern of isolation by distance. Bayesian structure analysis revealed three gene pools representing primary habitats on a coastal dune and two different inland dunes. All populations from secondary habitats were mixtures of the two inland dune gene pools, suggesting multiple colonization of post-mining areas from different source populations and hybridisation among source populations.
Discussion Populations of Labidura riparia from primary habitats deserve special conservation, because they harbour differentiated gene pools. The majority of the Labidura riparia populations, however, thrive in secondary habitats, highlighting their role for conservation.
Implications for insect conservation A dual strategy should be followed of conserving both remaining natural habitat harbouring particular intraspecific gene pools and secondary habitat inhabited by large admixed and genetically highly variable populations.
Reintroduction, i.e. the release of captive reared animals to the wild in an attempt to re-establish or augment a population, is an accepted tool in conservation of endangered species. Within the framework of the international project 'Reintroduction of the Bearded Vulture in the Alps' more than 60 captive reared birds were released since 1986 to reestablish the extinct population in the Alps. Because they are small, both the captive and the reintroduced population face the potentially disastrous risks of inbreeding and loss of genetic variability. To avoid inbreeding and to minimize the loss of genetic variability a genetic and demographic management is needed. Important information's for the planning and realization of such a management are the amount of genetic variability remaining in the captive and released populations, compared to large natural populations and the knowledge of the genealogical relationships among the individuals. In the project 'Reintroduction of the Bearded Vulture in the Alps' the genealogy of current individuals is available, but relationship among the 33 reproducing founders is almost completely unknown and there are no assessments of the genetic variability in natural and captive populations. The proposed project will provide the missing genetic data required for establishing a genetic management plan for the Bearded Vulture and will provide important tools for the long-term monitoring of the released population. In addition, the results gained in this study will improve Population Viability Analysis of Bearded Vulture populations. 1. Relatedness analysis of breeding network birds: Molecular genetic techniques (i.e micro satellites) will be used to provide information on the relative genetic similarity or distance among the founder individuals. 2. Comparison of genetic variability between natural populations and the breeding network: To determine whether there is a loss of genetic variability due to inbreeding and genetic drift, we will measure the genetic variability in both natural and captive populations of the Bearded Vulture using microsatelite markers. 3. Comparison of genetic variability between the original population in the Alps and the breeding network. All birds from the original population in the Alps are extinct.