Diet Variability of Two Convergent Natricine Colubrids in an Invasive-Native Interaction

In cases of introductions where the exogenous species is morphologically and ecologically very convergent with one, or more, of the native species, the potential for resource (trophic, territory, sun, shelter, etc.) competition is high. In this regard we investigated in 2007 and 2008 the potential role of trophic resource competition in the inva- sive-native species system Natrix maura-N. tessellata on the shores of Lake Geneva in Switzerland, of which this pa- per is the follow-up. We confirmed, among other results, a strong similarity in the diet of both species and were able to calculate a large overlap of their trophic niches (Metzger et al. 2009). In addition to that work we report herein patterns of within-year variation of the diets of both snakes, and report on the observation of individual foraging be- havior observed in an artificial environment.