Generalisation within specialization: inter-individual diet variation in the only specialized salamander in the world.

Andrea Costa,Sebastiano Salvidio,Antonio Romano,Bruno De Cinti,Giorgio Matteucci,Mario Posillico

doi:10.1038/srep13260

Abstract

Specialization is typically inferred at population and species level but in the last decade many authors highlighted this trait at the individual level, finding that generalist populations can be composed by both generalist and specialist individual. Despite hundreds of reported cases of individual specialization there is a complete lack of information on inter-individual diet variation in specialist species. We studied the diet of the Italian endemic Spectacled Salamander (Salamandrina perspicillata), in a temperate forest ecosystem, to disclose the realised trophic niche, prey selection strategy in function of phenotypic variation and inter-individual diet variation. Our results showed that Salamandrina is highly specialized on Collembola and the more specialized individuals are the better performing ones. Analyses of inter-individual diet variation showed that a subset of animals exhibited a broader trophic niche, adopting different foraging strategies. Our findings reflects the optimal foraging theory both at population and individual level, since animals in better physiological conditions are able to exploit the most profitable prey, suggesting that the two coexisting strategies are not equivalent. At last this species, feeding on decomposers of litter detritus, could play a key role determining litter retention rate, nutrient cycle and carbon sequestration.

Highlights

Specialization is typically inferred at population and species level but in the last decade many authors highlighted this trait at the individual level, finding that generalist populations can be composed by both generalist and specialist individual
As a matter of fact ecological specialization is reported at different biological levels[3]: population, species, community and, recently, specialization has been studied at the individual level[4]
All the individuals processed in this study are reproductive adults; their body size lies within a narrow range [40.40 (3.07) – Mean body length (SD)], and juveniles were not included in the analyses

Summary

Introduction

Specialization is typically inferred at population and species level but in the last decade many authors highlighted this trait at the individual level, finding that generalist populations can be composed by both generalist and specialist individual. Our findings reflects the optimal foraging theory both at population and individual level, since animals in better physiological conditions are able to exploit the most profitable prey, suggesting that the two coexisting strategies are not equivalent. At last this species, feeding on decomposers of litter detritus, could play a key role determining litter retention rate, nutrient cycle and carbon sequestration. Specialization is almost always inferred at species or population level, and only recently a new approach to the study of specialization emerged: the study of inter-individual diet variation[4] From this point of view the trophic niche of a population is seen as the result of the sum of the trophic niche of all individuals. Evidences of individual specialization are mainly based on dietary data, but evidences for habitat selection and other niche axes are documented, ranging from Plants to Mammals, through

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