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Zusammenfassung:
Determining the trophic niche width of an animal population and the relative degree to which a generalist population
consists of dietary specialists are long-standing problems of ecology. It has been proposed that the variance of stable isotope
values in consumer tissues could be used to quantify trophic niche width of consumer populations. However, this
promising idea has not yet been rigorously tested. By conducting controlled laboratory experiments using model consumer
populations (Daphnia sp., Crustacea) with controlled diets, we investigated the effect of individual- and population-level
specialisation and generalism on consumer d13C mean and variance values. While our experimental data follow general
expectations, we extend current qualitative models to quantitative predictions of the dependence of isotopic variance on
dietary correlation time, a measure for the typical time over which a consumer changes its diet. This quantitative approach
allows us to pinpoint possible procedural pitfalls and critical sources of measurement uncertainty. Our results show that
the stable isotope approach represents a powerful method for estimating trophic niche widths, especially when taking the
quantitative concept of dietary correlation time into account.
