Larval Salamandra drive temporary pool community dynamics: Evidence from an artificial pool experiment

We assessed the impacts of fire salamander larvae, Salamandra salamandra infraimmaculata, on community structure in replicated artificial pools. Because this predator metamorphoses and exits early from temporary pools, we also examined the resilience of the community for a short interval after Salamandra metamorphosed. Salamandra had extensive impacts on the food web. It reduced invertebrae species richness by 53%. Salamandra significantly reduced populations of three of the four numerically dominant invertebrates. It eliminated the large cladoceran, Simocephalus expinosus, while densities of the smaller cladoceran, Ceriodaphnia cf. quadrangula, were not affected. Presumably, this differential effect on the two cladoceran species was due at least in part to size-selective predation. Densities of the calanoid copepod. Arctodiaptomus similis, and Chironomidae were largely reduced by the salamander larvae. Hyla savignyi and Bufo viridis hatchlings were heavily preyed upon by Salamandra but surviving anuran tadpoles tended to be larger in the salamander pools than those in the control pools. Salamandra caused a trophic cascade; they indirectly caused an increase in periphyton and bacteria, presumably by reducing population of those species which graze on periphyton and bacteria and making more nutrients available through their excretion. Upon removing the salamandra, the invertebrate community in the former salamander pools then became indistinguishable from those of the control pools with respect to species richness after two weeks. Standing crop of filamentous algae became considerably higher in the control pools after the salamanders had been removed. Similarly, bacterial densities, higher in salamander pools during the salamander period, reversed to be higher in the controls during the post-salamander period although the difference was not statistically significant (p = 0.09). Our results indicate that larval Salamandra directly and indirectly has large effects on temporary pool community structure. Thus, the absence of this species, which is presently on the endangered species list in Israel, can have large consequences for the entire temporary pool community.