Species competing inter-specifically for resources has been well studied. Chances of invasion begins to increase once resources within a population begins to increase (Davis 2003), therefore creating instability for native populations. Competition for resources, such as habitat, could potentially lead to the exclusion of a species following “the competitive exclusion principle” by Hardin (1960). This principle means that when shared resources are met by coexisting species, competition will occur. Species which share similar morphology and are normally isolated from one another, tend to share the same resource requirements. An issue can occur when two such similar species occur in the same area, which normally do not coexist. This has occurred between two semi-aquatic Natricine snake species: viperine snake, Natrix maura (Lennaeus, 1758), and the dice snake, Natrix tessellata (Laurenti, 1768).
N. maura and N. tessellata populations used in this study are located between the cities of Lausanne and Villeneuve, in the canton of Vaud, Switzerland. These two populations reside on the shore of Lake Geneva (also known as Lake Leman). The area has been developed and consists of villages, vineyards, roads, and railways. For instance, much of the shoreline has railroads constructed along side of it. The riparian region of Lake Geneva consists of a rocky, partially vegetated slope terrain (Metzger et. al. 2009). N. maura is a native species to the shores of Lake Geneva, while N. tessellata (Morton 1925) has been introduced. Both species are found along this shoreline and it has also been documented that N. tessellata has partially colonize some habitat areas that are unfavorable to N. maura (Metzger et. al. 2009).
Ursenbacher et. al. (Submitted) previously documented N. maura to have an average decline of 4.4% each year. The exact reason for this decline is unknown, but it is thought to be correlated with the introduction of N. tessellata because of its similarities in ecological niches, such as habitat preference and diet it shares with N. maura (Metzger et. al. 2009). Due to N. maura’s decline, it has been listed as “critically endangered” in Switzerland (Monney and Meyer 2005). The natural distribution of N. tessellata does not include Lake Geneva and it is believed to have been released to Lake Geneva between 1925 and 1935 (Gautschi et al. 2002). This project focused on the study of the competition between both species at different levels: i) use of the habitat; ii) feeding behaviour; iii) thermal preferences.