Island biogeography along Norway’s west coast – an explorative citizen science approach

The theory of island biogeography is among the most recognized principles in the science of ecology. It states that the further away from the mainland, and the smaller an island is, the fewer species are present. Despite being one of the most island-rich countries worldwide, this theory has been poorly explored in Norway. Another important ecological principle, the latitudinal gradient of species richness, can be expected to be applicable to Norwegian islands due to the large latitudinal range of the Norwegian coast. Here, online databases and questionnaires of knowledgeable local residents provided data. A framework consisting of rules was set to include study species and create relevant sampling units (archipelagos). The present study thereby aimed at exploring, and to a degree evaluating these mixed methods, as well as describing the contemporary biogeography of a subsample of Norway’s oceanic islands. Overall, number of species present on the islands was found to increase with size of the archipelago and decrease with distance to mainland and latitude. Results for predicting specific species’ presence varied more. However, non-supportive results of the theory of island biogeography and the latitudinal gradient of diversity, were mostly explained by anthropogenic impact and species-specific habitat preferences. Additionally, the results suggested that local ecological knowledge was robust, although varying between species. In conclusion, the theory of island biogeography and the latitudinal gradient of species richness is applicable to Norwegian islands, although the results should be interpreted with caution. The underlying dynamics in local knowledge are expected to be complex, and study species should be selected with care when using the present methods. This study provides a first approach on the topic, and further research is recommended to focus on countryside biogeography through human impact as well as habitat-related predictors. Key words: Island biogeography, Latitudinal gradient, Rapoport’s rule, Citizen science, Species distribution, Coastal ecology