Size-Mediated Trophic Interactions in Two Syntopic Forest Salamanders

SIMPLE SUMMARY: Organisms compete for resources, such as food and space, and competition can occur in two ways: exploitative competition or interference competition. In exploitative competition, organisms consume the same limited resources, directly reducing the availability of those resources for other individuals, while in the case of interference competition, organisms actively prevent others from accessing resources, independently of resource availability. We tested for the presence and type of foraging competition in two species of forest-dwelling salamanders in Italy: Speleomantes strinatii and Salamandrina perspicillata. Our results suggested the presence of an interference/interaction occurring between the two species and affecting the foraging activity of the smaller one (Salamandrina perspicillata). This competitive interaction is size mediated and configured as interference competition rather than exploitative competition. ABSTRACT: Exploitative competition and interference competition differ in the way they affect re-source availability for competitors: in the former, organisms reduce resource availability for the competitors; in the latter, one organism actively prevents the competitor from accessing resources, independently of their availability. Our aim is to test for the presence of foraging competition in two forest-dwelling salamanders in Italy: Speleomantes strinatii and Salamandrina perspicillata. We also aim at testing for size-mediated competition. We obtained stomach contents from 191 sampled individuals by means of stomach flushing at 8 sampling sites where both species occur. We focused our analysis on the core prey taxa shared by both species: Collembola and Acarina. We found that the foraging activity of S. perspicillata is positively affected by body size and negatively affected by potential competitor’s activity on the forest floor during the sampling, which also significantly weakened the positive relationship with body size. These results suggest the presence of an interference/interaction occurring between the two species and affecting the foraging activity of S. perspicillata. This competitive interaction is size mediated and configured as interference competition rather than exploitative competition.