Table 1.
Overview of the experimental treatments specifying name, acronym, number of replicates and details of each treatment.
Table 2.
Number of individuals (metamorphs and larvae) used for isotopic analyses in each species and treatment.
Fig 1.
Stable isotope biplot of each amphibian species and sources of the experiment.
δ15N and δ13C values (mean ‰ ± SD) of the amphibians included in this study (Hyla meridionalis, Pelobates cultripes, Pelophylax perezi, and Triturus pygmaeus) pooled across all experimental treatments for a general view of differences in trophic status among species. Resources are also shown as means ± SD. The discrimination factors were added to the sources and not subtracted to the consumers to allow different discrimination factors to be assigned to different sources.
Fig 2.
Stable isotopic values for each amphibian species in the density treatments of the experiment.
δ15N and δ13C values (mean ‰ ± SE) of H. meridionalis, P. cultripes, P. perezi, and T. pygmaeus muscle in three different density treatments: low density of amphibian larvae (Low), a three-fold increase of the density from the low treatment (High), and exclusion of the competitive species P. cultripes (No Pc).
Fig 3.
Stable isotopic values for each amphibian species in the presence / absence of predators.
δ15N and δ13C values (mean ‰ ± SE) of H. meridionalis, P. cultripes, P. perezi, and T. pygmaeus muscle in the presence of native dytiscid larvae (free or caged, Nat Free or Nat Caged), or in the presence of invasive red swamp crayfish (free or caged, Inv Free,or Inv Caged), compared to absence of predators (Low).
Table 3.
Stable isotope composition (δ13C, δ15N), elemental composition (%C, %N) and discrimination factor (Δ13C, Δ15N) of the potential food sources for amphibian larvae in the experimental arrays of the study.
Fig 4.
Potential contribution of different food sources to the diet of each amphibian species.
Mean estimated proportion of each of the seven potential sources (detritus, algae, zooplankton, and four types of macrophytes) in the diet of three anuran species under five different ecological scenarios: low and high larval density, absence of spadefoot toads (P. cultripes), presence of free native dytiscid beetles, or presence of invasive red swamp crayfish. In the case of newts (T. pygmaeus), only two sources were considered since they do not consume macrophytes or algae. Also, no newts survived the presence of free crayfish.