Understanding factors that shape biological diversity are of great interest, especially in the present time, since biological diversity is under increasing threat. Biological diversity occurs at multiple levels from diversity in whole ecosystems to intraspecific biodiversity. Intraspecific biodiversity within northern freshwater fish has been found to be considerable. One such northern fish, the threespine stickleback (Gasterosteus aculeatus) shows important variations in morphology, diet and habitat use, where sympatric morph and/or species are common.

Lake Mývatn, is a shallow and eutrophic lake situated in North Iceland. This lake show strong spatial and temporal variation in several ecological factors, including resource availability. There are great fluctuations in macroinvertebrate population within the lake. Which are the main food sources of stickleback. A previous study showed clear spatial (among habitats) and temporal (between seasons) phenotypic variation, including variation in diet and feeding morphology. However this study only focused on one year so the generality of their finding needs to be confirmed in the light of the temporal variability of ecological conditions within Lake Mývatn. In addition it is important to study how temporally stable diet specializations across years. Another interesting aspect is to explore the relationship between morphology and diet on an individual basis. It is not unlikely to assume that the fluctuations in macroinvertebrate population within Mývatn are related to diet of stickleback and the level of specialization. Here, I introduce a project which explores further potential changes in diet specialization of Mývatn stickleback across years.