Freshwater Fish Community Responses to Climate Change and Invasive Species
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- Institutt for biologi 
Despite making up only a tiny proportion of the world’s aquatic surface area, freshwater ecosystems are home to a plethora of biodiversity, containing roughly 40% of all described fish species. Yet they’re also among the most threatened, due almost entirely to human activity. Two such activities are the spread of invasive species and climate change, both of which are capable of having profoundly negative impacts on lakes and rivers, from wiping out local species to upending entire food webs. There are measures which can be taken to help native species manage the combined impact of these two threats, but any successful conservation action takes money and time. As such, we need to know which freshwater regions are the most vulnerable to climate change and invasive species, and where conservation actions are likely to be effective. In my thesis, I lay the groundwork for a management tool which aims to predict a) where introduced species are likely to spread to and b) where they are likely to negatively affect local ecosystems. I also investigate the widely varying perceptions surrounding the concept of climate change as it relates to invasive species, and whether there is discord between researchers, managers and the public in regards to where conservation action is appropriate going forward. The results point to Scandinavian freshwaters seeing a shift towards warm-water species, potentially threatening culturally important species like the Arctic charr and brown trout. Fortunately, they also indicate that we are potentially able to identify areas most at risk of invasion, both here and globally. The will to prevent the spread of invasive species also exists, though there is still disagreement about what action should be taken if the inevitability of climate change affects this spread.