Date Published: October 18, 2018
Publisher: Public Library of Science
Author(s): Enrico Lunghi, Fabio Cianferoni, Filippo Ceccolini, Michael Veith, Raoul Manenti, Giorgio Mancinelli, Claudia Corti, Gentile Francesco Ficetola, Bruno Bellisario.
The trophic niche is a life trait that identifies the consumer’s position in a local food web. Several factors, such as ontogeny, competitive ability and resource availability contribute in shaping species trophic niches. To date, information on the diet of European Hydromantes salamanders are only available for a limited number of species, no dietary studies have involved more than one species of the genus at a time, and there are limited evidences on how multiple factors interact in determining diet variation. In this study we examined the diet of multiple populations of six out of the eight European cave salamanders, providing the first data on the diet for five of them. In addition, we assessed whether these closely related generalist species show similar diet and, for each species, we tested whether season, age class or sex influence the number and the type of prey consumed. Stomach condition (empty/full) and the number of prey consumed were strongly related to seasonality and to the activity level of individuals. Empty stomachs were more frequent in autumn, in individuals far from cave entrance and in juveniles. Diet composition was significantly different among species. Hydromantes imperialis and H. supramontis were the most generalist species; H. flavus and H. sarrabusensis fed mostly on Hymenoptera and Coleoptera Staphylinidae, while H. genei and H. ambrosii mostly consumed Arachnida and Endopterygota larvae. Furthermore, we detected seasonal shifts of diet in the majority of the species examined. Conversely, within each species, we did not find diet differences between females, males and juveniles. Although being assumed to have very similar dietary habits, here Hydromantes species were shown to be characterized by a high divergence in diet composition and in the stomach condition of individuals.
Trophic interactions are key determinants of the structure and dynamics of ecological niches in coexisting species [1–4]. Specifically, the trophic niche defines the role of a species in a local food web, identifying energy transfer routes from food resources [5–7]. The width of the trophic niche is mostly defined by the selectivity of the species , which contribute in defining the range of food resources which species are able to feed on [9–11]. The width and other features of a species’ trophic niche are often genetically determined [12,13]. However, species trophic niche is generally characterised by a certain degree of intrinsic plasticity, allowing diet shifts when competition occurs, but also to cope with temporal and local variability of the available resources [8,14]. Indeed, beside the intrinsic characteristics of individuals, the realised trophic niche is strongly related to the ability to persist in an environment where food resources vary in space and time , and thus to the capacity to obtain from different subsets of resources the complex combination of elements needed to fulfil physiological and metabolic requirements [16–18]. In wide-ranging species, it is likely that populations forage in environments differing in terms of resource availability and trophic networks [16,19]. Therefore, conspecifics of different populations adapt their feeding habits to the local food availability . In addition, seasonality produces a natural fluctuation of resource, which forces periodic variation in species diet composition [16,20]. A further change in dietary habits occurs throughout individual ontogenesis. Individuals require different sets of nutrients during their life stages, and thus prey selection depends on the nutritional needs [21–24]. Moreover, competition may also play a role in shaping species trophic niche [25–27]. Indeed, when resources are limited, species can switch to a sub-optimal set of resources or, alternatively, change their feeding habits to equally profitable ones to coexist with higher competitors [28–31].
Hydromantes salamanders show a wide trophic spectrum, being able to prey on a very large variety of invertebrate prey (belonging to at least 35 different Orders) (Tab. 3). Our analyses suggest that the feeding ecology of these salamanders is shaped by the interplay between life stage and seasonality, highlighting the complexity of factors determining diet variation.
This study provides the broadest assessment of diet variation in European Hydromantes species. The diet of these generalist species shows strong seasonal variation, suggesting the important role of the temporal abundance of prey. High turnover of prey likely occur where environmental features are less stable (i.e., shallow cave areas, outdoor), thus highlighting the importance of the connection between the underground and the outdoor environments. Salamanders can have a key functional role in the ecosystems where they live, as they can reach very high abundance and can thus play a key functional role in forest floor communities . For example, salamanders are in a critical intermediate position in the food web, representing a crucial node for the flow of energy and matter between different environments [80,92,93]. Although plethodontids are among the terrestrial salamanders reaching the highest abundances [80,94] most of the studies on the feeding ecology and the functional role of plethodontids are limited to the North American species. Our study is a first attempt to unveil the trophic ecology of different species of European Plethodontids that can be a basis for future investigations highlighting the role of these salamanders in the ecosystems.