Persistence of introduced populations of Roesel's bush-cricket Metrioptera roeseli in a patchy landscape

Introductions are likely to increase in importance as a conservation tool. Still lacking are studies directed at the distinct aspects of species introduction and their underlying assumptions. One of the most important factors determining colonization success is the propagule size. Other factors of importance for successful colonization include target area suitability. This thesis shows how different landscape and population variables affects individuals and thereby populations. Different sized propagules of Roesel's bush-cricket Metrioptera roeseli were experimentally introduced onto 70 habitat islands, previously uninhabited by the species, in south-eastern Sweden. The areas of introduction were carefully monitored for six years. The study showed that large propagules resulted in larger populations during the years following introduction. Propagule size had a significant effect on colonization success, i. e. large propagules were more successful in colonizing new patches. Suitable habitats were important for population persistence. Connectivity in the form of linear landscape elements and nodes were important for colonization success, population growth and dispersal. Linear landscape elements and nodes also reduced the negative effects of isolation from suitable habitat. I found that individuals avoided habitat edges and that corridors were a preferred alternative for dispersal. The corridor showed a steering effect and directed individuals to the connected habitat patch. Within six years, morphological differences in the populations could be measured. Male trait sizes were positively affected by numbers of nodes in the landscape, by the amount of linear elements, patch size, and growth rate of the population. Female trait sizes were most affected by the growth rate and the density of the population. Males showed less asymmetry in landscapes with more good habitat and connectivity, and also if they came from large initial propagules. These results stress the importance of connectivity in the landscape for population survival in both short and long term, by reducing the negative effect that habitat fragmentation has on small populations.