Abstract
Intraspecific trait variation in generalist animals is widespread in nature, yet its effects on community ecology are not well understood. Newts are considered opportunistic feeders that may co-occur in different syntopic conditions and represent an excellent model for studying the role of individual feeding specialization in shaping the population dietary strategy. Here, we investigated the diet of three newt species from central Italy occurring in artificial habitats in different coexistence conditions to test the predictions of the niche width (NW) variation hypotheses. Population NW did not vary among species and between presence and absence of coexisting species. An overall positive relationship between individual specialization and population NW was observed. However, this pattern was disrupted by the condition of syntopy with newt populations showing an individual NW variation invariant with population NW in presence of coexisting species, whereas it was larger in populations occurring alone. The observed pattern of newt behavior was not consistent with any of the proposed scenarios. We found a consistent pattern with the degree of individual specialization being (1) size-dependent (specialized individuals increasing within larger sized species) and (2) assemblage-complexity-dependent (specialized individuals increasing in syntopic populations in comparison to singly populations).
Highlights
Urodeles are important elements of freshwater vertebrate communities either as prey or as predators [1,2,3,4] contributing to most of the total predator biomass in specific study areas [5]
Body size differed among study sites and intersexual differences were found within each newt species, with females being larger than males (Table 1; Figure 3A)
Population niche breadth is thought to represent a balance between the diversifying effect of intraspecific competition and the constraints imposed by interspecific competition [51]
Summary
Urodeles are important elements of freshwater vertebrate communities either as prey or as predators [1,2,3,4] contributing to most of the total predator biomass in specific study areas [5]. As predators of invertebrates and small vertebrates, they modulate energy pathways by decreasing the abundance of competitively dominant preys and increasing taxa diversity in lower trophic levels [12]. Through their dual life cycle, they serve as connecting pathways for energy between aquatic and terrestrial environments affecting prey communities in both habitat types [13]. It has been postulated that within-population niche variation can stabilize population and community dynamics [24], with environments having greater resource diversity favoring ecological diversity among consumers via disruptive selection or phenotypic and ecological plasticity or, as an alternative mechanism, that niche variation may be a consequence of neutral genomic diversity in more abundant populations [25]
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