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

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.

Comparison of diet and prey selectivity of the Pyrenean desman and the Eurasian water shrew using next-generation sequencing methods

“…This suggests that the identity of prey taxa is not the most important criteria for both mammals prey selection and that they may exhibit some tolerance to variation in prey community composition. Hence, stream community changes due to anthropogenic impacts on river ecosystems should have moderate consequences (Costa et al, 2015) as long as food resources remain abundant enough in their respective foraging habitats. However, pressures on prey communities could increase the trophic overlap between the two species as well as with others potential competitors.…”

“…It depends on the balance between the energy provided by prey consumption and the energetic costs of foraging under water. The most valuable resources may thus correspond to easy-to-catch prey with low mobility (e.g., Trichoptera) and/or high abundance (e.g., Gammaridae), soft-bodied prey that can be completely digested (e.g., in contrast with small and chitinous Hydracarina or Coleoptera, Costa et al, 2015) or large prey (Bertrand, 1994). In this study, invertebrates with hard and chitinous bodies (e.g.…”

Responses in the diet composition of the Common frog (Rana temporaria) to the stochastic gradation of Autumnal moth (Epirrita autumnata) larvae

“…However, it also stresses a potential bias inherent to short-term monitoring studies. When an animal species is selected for long term monitoring for conservation purposes, the disclosure of its feeding ecology can be a crucial element of the project (Kovács et al 2007, Costa et al 2015, Liess 2015. Our results clearly show that a one-year study on the feeding ecology of an opportunistic species might be highly misleading if the sampling year is extraordinary in the composition of food supply.…”

“…Mite and ant eating is common amongst tropical poison frog species (Woodhead et al 2007, Sabagh et al 2012). Mite eating is also known in specialized foreger salamander Salamandrina perspicillata (Costa et al 2015). Boelter et al (2012) proved that invasive Lithobates catesbeianus consume other frog species selectively and in high volume.…”

Opposing Lethal Wildlife Research When Nonlethal Methods Exist: Scientific Whaling as a Case Study

“…This has applicability for terrestrial wildlife research as well. For example, in dietary studies, nonlethal sampling of salamanders (Crovetto et al 2012;Costa et al 2015) and lizards (Crovetto and Salvidio 2013) by stomach flushing and fecal analyses has already replaced the lethal methods once used. Lethal methods may be traditional in some cultures and conservation disciplines but that doesn't make them a moral ''right'' within a global community, or a ''necessary evil'' through which information is gathered.…”