The trophic niche of subterranean populations of Speleomantes italicus

Abstract

The determination of a species trophic niche can clarify its functional role within a food web and how prey resources are used in relation with the spatial and temporal variability of environmental conditions. This information may result particularly useful for the implementation of conservation plans of endangered species having a cryptic behaviour or living in places difficult to be surveyed. Here we present the first long-term study on the trophic niche of the Italian cave salamander Speleomantes italicus, a strictly protected facultative cave species that seasonally exploits surface environments (e.g., forested areas) as well as both natural and artificial subterranean environments. We analysed the diet variation of six populations of S. italicus inhabiting natural caves, surveyed 24 times in a full year. During the surveys, all sampled individuals were subjected to stomach flushing and the ingested prey were identified and enumerated; furthermore, salamanders' body condition was also evaluated. The results of the analyses provided the first comprehensive, year-round assessment of the diet for a Speleomantes species. Remarkable divergences in terms of trophic niche and body condition were observed between the studied populations. We found a discrepancy in the foraging activity of the populations located in different areas; specifically, the individuals that experienced sub-optimal microclimatic conditions poorly performed in foraging. Furthermore, we found temporal and spatial variability in the body condition of individuals. Our study highlighted a remarkably high spatial and temporal divergence in the trophic habits of conspecific populations, a feature that may represent one of the major factors promoting the variability of multiple population traits.

Figure 1

The map of the study area indicating the location of the studied caves. Three caves were located in the municipality of Pistoia (red circles; S_italicus5, S_italicus6, S_italicus7), 1 in the municipality of Vaiano (yellow circle; S_italicus4) and 2 in the municipality of Prato (grey circles; S_italicus2, S_italicus3). No detailed information on sampled locations are provided to ensure species protection. In the bottom-left corner an individual of Speleomantes italicus (the image is taken from the dataset published by Lunghi et al., as well as the populations code). Map was built using the free software QGis v. 3.8.3 (https://qgis.org/en/site/).

Figure 2

nMDS plot of temporal trajectories in dietary variations among the six populations of Speleomantes italicus under analysis; in the caption, the months when individuals were analysed are reported in parentheses.

Figure 3

PERMANOVA analysis testing the effects of the factors “population” (fixed), “month” (fixed, repeated) and “individual” (random, nested within “population”) on Speleomantes italicus dietary habits: results of the pair-wise tests performed on the 46 possible combinations population/month. Noticeably, only16 were statistically significant (P < 0.05), and occurred in the months May–June and September–October.

Figure 4

(A) Average number and the diversity (Shannon index) of consumed prey in the six populations of Speleomantes italicus. (B) Annual variation of body condition index (BCI) for the same populations. Numbers on x axis indicate the months; January is not included as no salamanders were captured.

Figure 5

Microclimatic data recorded throughout a year nearby the entrance of the studied caves. Data on air temperature (A) and relative humidity (B) were monthly collected in a shaded area in the proximity (about 5 m) of the main entrance for each cave. Numbers on x axis indicate months. Data is retrieved from.