Eco-evolutionary dynamics in the Baltic Sea: Distribution and impact of threespine stickleback phenotypes in a changing environment

The restoration of degraded habitats is a complicated process which needs to consider all ecological drivers of ecosystem structure including evolution. Ongoing evolution can change a population’s traits, and therefore functional role, which can modify ecosystem structure. Understanding eco-evolutionary dynamics, when ecological and evolutionary processes act simultaneously to constantly influence one another, is of vital importance when maintaining or restoring habitats based on ecosystem structure. In this thesis, I aimed to provide novel insights into the eco-evolutionary dynamics of the threespine stickleback (Gasterosteus aculeatus) in coastal Baltic Sea habitats. A better understanding of the role that stickleback play in these habitats was needed as the population has seen rapid expansion and diversification following changes to trophic structure of offshore and inshore Baltic Sea habitats. In this thesis I provide evidence of habitat and dietary differentiation of stickleback plate phenotypes. Utilizing data collected from 32 shallow bays along the central Swedish coast, I show that overall stickleback abundance and relative abundance of incompletely-pated stickleback increases with increasing topographical openness of bays and decreases with increasing piscivorous fish abundance. I also present data that suggests a change in trophic structure of coastal bays characterized by an increase in stickleback abundance and decrease in juvenile predatory fish abundance. I also demonstrate that stickleback communities of different plate phenotype composition have different effects on lower trophic level resources due to dietary differentiation and present evidence that through dietary differentiation and different responses to warming, different plate phenotype compositions may differentially affect ecosystem structure.