Historical food web structure of Swedish rivers: how damning are dams?

Documenting long-term changes in aquatic ecosystems is notoriously difficult; however, food webs are a central organizing theme in ecology. Food webs are special descriptions of biological communities focused on trophic interactions between consumers and resources. They provide a means of analyzing interrelationships among community structure, stability, and ecosystem processes, and how these attributes are influenced by environmental change and disturbance. Well-functioning food webs are fundamental in sustaining rivers as ecosystems and maintaining associated aquatic and terrestrial communities.

Although challenges to conducting food webs studies in extant communities of rivers are significant, they pale in comparison with understanding what has affected food webs over longer time periods (decades to centuries). To gain a long-term perspective on changes in food webs, one option is to use museum specimens and stable isotope analysis. These provide a unique opportunity to look at food web drivers over long timescales.

Sampling Design

Museum collections and species surveys by government agencies represent critical infrastructure and provide data useful for analyzing long-term environmental impacts, and can be particularly valuable for studying food webs. To gain a long-term perspective on changes in food web characteristics that I hypothesize to be present, I will measure trophic position, food chain length, and food sources of museum specimens of aquatic consumers from two rivers in Southern Sweden, the Kävlinge and the Höje. We will sample mussels, to represent the base of the food web (both marine and freshwater species), with scrapings from their periostracum. We will sample representative fish species with fin clips, scale collections or muscle biopsies. And we will collect fur samples or skull scraping or drillings from terrestrial mammals that are known to feed on aquatic organisms (i.e. mink, otter, fox). We will look at two general time frames, samples were taken before 1910 and after 1990, to get a 100 year perspective on changes in food webs of the two rivers.

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