Abstract:Information on individual trophic specialization may be relevant to better understand the ecological adaptation of populations to their environment and the evolution of their realized trophic niche. In this study, we analysed the trophic specialization at the individual level in a population of the plethodontid Northwest Italian Cave Salamander (Speleomantes strinatii (Aellen, 1958)), a terrestrial generalist predator. Salamanders were sampled in northwestern Italy on the forest floor in autumn (n = 49) and sp… Show more
“…Distinguishing between these non-exclusive processes is not easy; moreover, we did not measure variation of prey abundance. However, Hydromantes salamanders are generalist predators consuming a wide range of prey, and are able to feed on most of the underground and outdoor invertebrates 24 , 25 ; thus we expect that prey is generally present throughout the whole species range. Nevertheless, detailed analyses are needed to assess whether the spatial variation of prey availability determines the differences in feeding performance across populations.…”
Section: Discussionmentioning
confidence: 99%
“…Furthermore, H . flavus is a generalist predator of small invertebrates 24 , 25 , has few known predators, and there are no other terrestrial salamanders (i.e., main competitors) within its distribution range 26 , thus we do not expect major effects of biological interactions on local abundance 5 . Figure 2 Distribution area of Hydromantes flavus , and environmental suitability estimated through the ensemble forecasting of multiple species distribution models.…”
Species can show strong variation of local abundance across their ranges. Recent analyses suggested that variation in abundance can be related to environmental suitability, as the highest abundances are often observed in populations living in the most suitable areas. However, there is limited information on the mechanisms through which variation in environmental suitability determines abundance. We analysed populations of the microendemic salamander Hydromantes flavus, and tested several hypotheses on potential relationships linking environmental suitability to population parameters. For multiple populations across the whole species range, we assessed suitability using species distribution models, and measured density, activity level, food intake and body condition index. In high-suitability sites, the density of salamanders was up to 30-times higher than in the least suitable ones. Variation in activity levels and population performance can explain such variation of abundance. In high-suitability sites, salamanders were active close to the surface, and showed a low frequency of empty stomachs. Furthermore, when taking into account seasonal variation, body condition was better in the most suitable sites. Our results show that the strong relationship between environmental suitability and population abundance can be mediated by the variation of parameters strongly linked to individual performance and fitness.
“…Distinguishing between these non-exclusive processes is not easy; moreover, we did not measure variation of prey abundance. However, Hydromantes salamanders are generalist predators consuming a wide range of prey, and are able to feed on most of the underground and outdoor invertebrates 24 , 25 ; thus we expect that prey is generally present throughout the whole species range. Nevertheless, detailed analyses are needed to assess whether the spatial variation of prey availability determines the differences in feeding performance across populations.…”
Section: Discussionmentioning
confidence: 99%
“…Furthermore, H . flavus is a generalist predator of small invertebrates 24 , 25 , has few known predators, and there are no other terrestrial salamanders (i.e., main competitors) within its distribution range 26 , thus we do not expect major effects of biological interactions on local abundance 5 . Figure 2 Distribution area of Hydromantes flavus , and environmental suitability estimated through the ensemble forecasting of multiple species distribution models.…”
Species can show strong variation of local abundance across their ranges. Recent analyses suggested that variation in abundance can be related to environmental suitability, as the highest abundances are often observed in populations living in the most suitable areas. However, there is limited information on the mechanisms through which variation in environmental suitability determines abundance. We analysed populations of the microendemic salamander Hydromantes flavus, and tested several hypotheses on potential relationships linking environmental suitability to population parameters. For multiple populations across the whole species range, we assessed suitability using species distribution models, and measured density, activity level, food intake and body condition index. In high-suitability sites, the density of salamanders was up to 30-times higher than in the least suitable ones. Variation in activity levels and population performance can explain such variation of abundance. In high-suitability sites, salamanders were active close to the surface, and showed a low frequency of empty stomachs. Furthermore, when taking into account seasonal variation, body condition was better in the most suitable sites. Our results show that the strong relationship between environmental suitability and population abundance can be mediated by the variation of parameters strongly linked to individual performance and fitness.
“…Salamanders of the genus Hydromantes are nonobligate cave dwellers endemic to Italy and France, using subterranean environments for shelter as they offer a combination of abiotic conditions suitable for their cutaneous respiration (Spotila 1972, Lanza et al 2006. They prey upon invertebrates in the neighborhood of the cave's entrance (Salvidio et al 2015, Lunghi et al 2018a; accordingly, their trophic activity is strongly influenced by epigean climatic conditions (Lunghi et al 2015(Lunghi et al , 2018c. Moreover, Hydromantes populations are characterized by a high site fidelity and restricted home ranges (<80 m: Lanza et al 2006) to the point that populations from different caves can be considered isolated (Salvidio 2013, Lunghi andBruni 2018).…”
Individual diet specialization (IS) has important community-and populationlevel implications and its ecological drivers are actively investigated. Here, to test the hypothesis that local environmental conditions may influence IS in wild populations, we analyzed the stomach contents of 395 individuals from eight populations of five allopatric species of European cave salamanders (genus Hydromantes). We assessed whether their degree of individual diet specialization (1) scaled positively with the respective niche widths, in agreement with Van Valen's niche variation hypothesis (NVH), and (2) could be predicted by satellite-derived climatic and vegetation characteristics of the sites where the populations live. Consistent with the NVH, the degree of individual diet specialization increased with the populations' total niche width. Furthermore, two variables describing local nonarboreal vegetation cover and habitat heterogeneity successfully predicted the variation in individual specialization across the eight populations. Climatic factors had a generally low predictive power, with individual specialization in low-and high-elevation populations showing contrasting patterns of co-variation with air temperature in the warmest quarter of the year. However, independently from elevation, specialization peaked under conditions of high nonarboreal vegetation cover and high precipitation regimes. We discussed the results against two mutually nonexclusive scenarios hypothesizing different mechanisms linking environmental factors to salamanders' trophic strategy at an individual and population level. We concluded that satellite-derived climatic and vegetation variables to date generally adopted to model Grinnellian niches might also be useful in predicting spatial variations in dietary habits of populations, that is, their Eltonian niches.
“…The feeding habits of aquatic developmental stages of salamanders are well documented, being able to feed on a wide variety of invertebrate prey captured close to the bottom as well as terrestrial invertebrates on the water surface [14][15][16][17][18]. In general, salamanders have been considered as generalist-opportunist foragers, with remarkable ontogenetic dietary shifts, and their diets reflect the relative abundance of prey in the environment [14,[18][19][20]. In addition, salamanders have been widely used as model organisms to test key ecological questions related to, for example, top-down trophic cascades, nutrient cycling processes, and carbon retention in ecosystems e.g., [3,12,21,22].…”
Many species of salamanders (newts and salamanders per se) have a pivotal role in energy flow pathways as they include individuals functioning as prey, competitors, and predators. Here, I synthesize historic and contemporary research on the reciprocal ecological role of salamanders as predators and prey in aquatic systems. Salamanders are a keystone in ecosystem functioning through a combination of top–down control, energy transfer, nutrient cycling processes, and carbon retention. The aquatic developmental stages of salamanders are able to feed on a wide variety of invertebrate prey captured close to the bottom as well as on small conspecifics (cannibalism) or other sympatric species, but can also consume terrestrial invertebrates on the water surface. This capacity to consume allochthonous resources (terrestrial invertebrates) highlights the key role of salamanders as couplers of terrestrial and aquatic ecosystems (i.e., aquatic–terrestrial linkages). Salamanders are also an important food resource for other vertebrates such as fish, snakes, and mammals, covering the energy demands of these species at higher trophic levels. This study emphasizes the ecological significance of salamanders in aquatic systems as central players in energy flow pathways, enabling energy mobility among trophic levels (i.e., vertical energy flow) and between freshwater and terrestrial habitats (i.e., lateral energy flow).
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