Trophic strategies of two newt populations living in contrasting habitats on a Mediterranean island

Feeding ecology of the endangered toad Bombina pachypus in central Italy

Anurans are generalist opportunistic consumers, but many species show some degree of diet specialization. Within populations, individuals may specialize on specific dietary resources (individual specialization). Indeed, generalist populations may be composed of individuals using the whole range of available resources or by diverse individuals exploiting specific food items. Based on the Niche Variation Hypothesis (NHV) an increase in population niche width may be related to higher incidence of individual specialization. We analysed the feeding ecology of the endangered toad Bombina pachypus (Bonaparte, 1838) in central Italy. Bombina pachypus showed a generalist feeding strategy, wide trophic niche, high individual generalization, and a predominance use of terrestrial resources. The study species inhabits seasonal habitats determining variation in food availability and diversity, and this may have driven toads to be unselective and consume almost any encountered palatable item. The absence of sexual size dimorphism may explain the absence of trophic differentiation between sexes. The analysis of individual feeding traits revealed a week degree of individual specialization positively correlated to niche width partly supporting NHV. The obtained information can be used for the implementation of effective conservation strategies of locally imperilled species, especially those breeding in temporary ponds.

Weighted individual-resource networks in prey-predator systems: the role of prey availability on the emergence of modular structures

Ecological networks, usually depicting interactions among species, have been recently down-scaled to the individual level, permitting description of patterns of inter-individual resource variation that are usually hindered at the species level. Optimal diet theory (ODT) models, applied to prey-predator systems, predict different patterns of nestedness and modularity in the network, depending on the available resources and intra-specific competition. The effect of resource availability on the emergence of networks structures, and ODT framework, has not yet fully been clarified. Here, we analyzed the structural patterns of individual-resource networks in 3 species of Mediterranean salamanders, in relation to changes in prey availability. We used weighted individual-resource network metrics to interpret the observed patterns, according to 3 ODT models. We found significant nestedness recurring in our study system, indicating that both selective and opportunistic individuals occur in the same population. Prey diversity, rather than abundance, was apparently related to inter-individual resource variation and promoted the emergence of significant modularity within all networks. The observed patterns of nestedness and modularity, together with the variation in resource diversity and intra-specific competition, are in agreement with the distinct preferences model of ODT. These findings suggest that in the focal prey-predator systems, individuals were able to perceive changes in prey diversity and to exploit in different ways the variations in composition of available resources, shifting their diet assembly rules accordingly. Our findings also confirm that the use of weighted individual-resource networks, in prey-predator systems, allows to disclose dynamics that are masked at the species or population level.

Reciprocal Role of Salamanders in Aquatic Energy Flow Pathways

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).