Abstract
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.
Highlights
Trophic interactions are key determinants of the structure and dynamics of ecological niches in coexisting species [1,2,3,4]
The trophic niche defines the role of a species in a local food web, identifying energy transfer routes from food resources [5,6,7]
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 [15], and to the capacity to obtain from different subsets of resources the complex combination of elements needed to fulfil physiological and metabolic requirements [16,17,18]
Summary
Trophic interactions are key determinants of the structure and dynamics of ecological niches in coexisting species [1,2,3,4]. The width of the trophic niche is mostly defined by the selectivity of the species [8], which contribute in defining the range of food resources which species are able to feed on [9,10,11]. Species trophic niche is generally characterised by a certain degree of intrinsic plasticity, allowing diet shifts when competition occurs, and to cope with temporal and local variability of the available resources [8,14]. 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 [15], and to the capacity to obtain from different subsets of resources the complex combination of elements needed to fulfil physiological and metabolic requirements [16,17,18]. When resources are limited, species can switch to a sub-optimal set of resources or, alternatively, change their feeding habits to profitable ones to coexist with higher competitors [28,29,30,31]
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