Browsing by Subject "fasilitaatio"

Beavers (Castor spp.) are species which change the environment and by doing so maintain and create habitats which are important for many other species. That is why beavers are called as ecosystem engineers, key species and facilitators. Beaver creates a pond which offers shelter and food for example for the waterfowl. Previous studies have shown that especially the teal (Anas crecca) benefits from the beaver. Invertebrates, such as water fleas, are numerous in beaver ponds and the teal uses them as nutrition. Because of their feeding habits teals are also able to colonise new habitats, like beaver ponds, quickly. The aim of the thesis was to study the effect of the beaver to the teal on patch and landscape scale. Two landscapes - Evo and Nuuksio - were used in this study. Evo represents a landscape with beaver and Nuuksio without beaver. The pair and brood densities and brood production were compared on the patch scale before the beaver flood and during the beaver flood in order to find out whether the densities and brood production are higher during the flood. In addition, densities and brood production were compared in beaver occupied lakes and non-beaver lakes in Evo. In the landscape scale the annual pair and brood densities and brood production were compared between Evo and Nuuksio. Furthermore, the general linear mixed effect model was used to examine which variables explain the pair and brood numbers in the landscape scale. The results indicated that the brood density and brood production were higher during the beaver flood than before which means that the effect of the beaver to the teal was positive on the patch scale. Instead there was no positive effect on the pair density. Comparison between the beaver and non-beaver lakes showed that brood density and brood production were also higher on the beaver lakes and again there was no effect on pair density. The results also indicated that the pair and brood densities were higher in Evo than in Nuuksio but the brood production did not differ statistically between the regions. The modelling showed that the model which included location as an explanatory variable explained the pair numbers well and the model with location and spring flood as explanatory variables explained brood numbers well. However, there was some uncertainty considering the selection of the most suitable model due to the relatively small differences between the AIC values. As a conclusion it could be said that the facilitative effect of beaver appears both on patch and landscape scale. The beaver effect was especially important for the teal broods which has been noticed also in previous studies. As the beaver effect seems to be important on both scales one might consider whether the ecosystem engineering by beaver should be used in restoration purposes on those areas where the waterfowl density is low.