Entomologica Romanica Vol. 17 / 2012
2012
Table. 3. Number of studied amphibians, the frequency of vegetal remains, shed skin, inorganic elements, number of preys, average and maximum number of prey/individual, the diversity and similarity of the food. from the samples and most of them identified up to species level, they probably being ingested with only few hours before sampling. Nevertheless there were cases when isopods were highly digested, so the identification of species being impossible. Thus, in some cases we could identify only the genus, either because isopods were in an advanced digestion stage, or because males were missing. The fact that not all terrestrial isopodes consumed by frogs can be determined was previously recorded (Tomescu et al. 2010). Isopods were identified using scientific literature (e.g. Radu 1983, 1985), considering the present used nomenclature (Schmalfuss 2003). Along with terrestrial isopods, other prey groups ingested by both amphibian species were identified. Afterwards, we calculated the percentage abundance (%A) and frequency of occurrence (%f) in the case of each prey taxa. Also, we calculated the average number of preys/individual. The food diversity was calculated using Shannon-Wiever index (Shannon and Wiever 1949) and the similarity using Sorrensen index (see in: Magurran 1988). In order to establish the significance of the differences between the food composition of both amphibian species, the Mann-Whitney test was applied (Zar 1999). In the case of isopod species, we calculated the percentage abundance of each species from the total species consumed by amphibians. Also, we calculated the frequency with wich each species of isopod was consumed by the amphibians that have fed on terrestrial isopods. Results Terrestrial isopods represented a relatively important part of the food consumed by the two amphibian species from Ceamurlia de Jos, being consumed by numerous frogs. However, the frequency of consumption of isopods differs according to the amphibian species. Thus, in the case of P syriacus 38.89 % of individuals consumed terrestrial isopods, and in the case of E. viridis, the percentage was higher, reaching 52.32 % (Table 1). As a total, E. viridis and P syriacus consumed terrestrial isopods belonging to 5 species {Trachelipus rathkei, Porcellionides pruinosus, Porcellio laevis, Armadillidium vulgare and A. versicolor). Out of these, P syriacus has consumed only three species, while E. viridis has fed with individuals of all 5 species (Table 2). In the food of E. viridis were identified, at least to the genus level, 57 terrestrial isopod individuals. In the food of P syriacus were identified 38 terestrial isopod individuals. As well as the frequency, the percentage abundance of terrestrial isopods differs depending on amphibian species (Table 1). Although terrestrial isopods represented an important part of both amphibian species' food, they did not dominate, occupying only the second place as percentage abundance and also as frequency (Table 1). The majority of the consumed preys, by the two amphibian species from Ceamurlia de Jos, were Coleopterae. This is also valid in the case of frequency, where the first place is also taken by coleoptera. At E. viridis, on the second place, equally with isopods are ranked formicids, and at P syriacus on the second place, equally with isopods, were consumed araneas and oligocheta (Table 1). Although both amphibian species consumed approximately the same prey taxa, between their feedings there are some differences. Thus, E. viridis has a higher food diversity (H = 2.40 in comparison with H = 1.83 at P. syriacus). At the same time, E. viridis consumed a higher number of prey taxa, 25 than 21 at P. syriacus (Table 3). On the hole, in the food of these two amphibian species were recorded 28 prey taxa, from which 18 were consumed by both species. The high number of the common prey taxa determined probably the not significant differences between the two species' feeding (p=0.36). Although E. viridis consumed a higher number of prey taxa, the number of preys is lower than in the case of P syriacus. As well as, at E. viridis the average number of preys / individual was higher (44 than 34 at P syriacus). The high number of preys consumed by one individual of was due to isopods. One E. viridis individual consumed 26 terrestrial isopods along with other 18 preys. All the 39 studied amphibians presented stomach content. The lowest number of preys / individual was 2 and it was registered in the Species Epidalea viridis Pelobates syriacus No. of analysed individuals 21 18 Fragments of shed-skin 14.29 11.11 Inorganic elements 38.10 5.56 No. of consumed preys 266 284 Maximum no of preys/ individual 44 34 Average no of preys / individual 12.66 15.77 Diversity 2.40 1.83 Similarity 0.32 0.35 7