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Generalisation within specialization: inter-individual diet variation in the only specialized salamander in the world.

Costa A, Salvidio S, Posillico M, Matteucci G, De Cinti B, Romano A - Sci Rep (2015)

Bottom Line: Our results showed that Salamandrina is highly specialized on Collembola and the more specialized individuals are the better performing ones.Our findings reflects the optimal foraging theory both at population and individual level, since animals in better physiological conditions are able to exploit the most profitable prey, suggesting that the two coexisting strategies are not equivalent.At last this species, feeding on decomposers of litter detritus, could play a key role determining litter retention rate, nutrient cycle and carbon sequestration.

View Article: PubMed Central - PubMed

Affiliation: Consiglio Nazionale delle Ricerche, Istituto di Biologia Agroambientale e Forestale (CNR-IBAF), Area di Ricerca Roma 1, Via Salaria km 29, 300-00015. Monterotondo (RM) (Italy).

ABSTRACT
Specialization is typically inferred at population and species level but in the last decade many authors highlighted this trait at the individual level, finding that generalist populations can be composed by both generalist and specialist individual. Despite hundreds of reported cases of individual specialization there is a complete lack of information on inter-individual diet variation in specialist species. We studied the diet of the Italian endemic Spectacled Salamander (Salamandrina perspicillata), in a temperate forest ecosystem, to disclose the realised trophic niche, prey selection strategy in function of phenotypic variation and inter-individual diet variation. Our results showed that Salamandrina is highly specialized on Collembola and the more specialized individuals are the better performing ones. Analyses of inter-individual diet variation showed that a subset of animals exhibited a broader trophic niche, adopting different foraging strategies. Our findings reflects the optimal foraging theory both at population and individual level, since animals in better physiological conditions are able to exploit the most profitable prey, suggesting that the two coexisting strategies are not equivalent. At last this species, feeding on decomposers of litter detritus, could play a key role determining litter retention rate, nutrient cycle and carbon sequestration.

No MeSH data available.


Related in: MedlinePlus

Histograms of distributions of within-individual component/trophic niche width (WIC/TNW) ratio and individual specialization (IS) indices obtained by Monte Carlo resampling procedure, both for autumn and spring data.Vertical broken lines show the 95% confidence limits of the simulated distribution, while the vertical solid line shows the actual index value for the original data.
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f3: Histograms of distributions of within-individual component/trophic niche width (WIC/TNW) ratio and individual specialization (IS) indices obtained by Monte Carlo resampling procedure, both for autumn and spring data.Vertical broken lines show the 95% confidence limits of the simulated distribution, while the vertical solid line shows the actual index value for the original data.

Mentions: The Total Niche Width (TNW) of the population in Autumn is wider than in Spring (TNW = 1.16—0.83; in Autumn and Spring, respectively). The Within Individual Component of the trophic niche (WIC) resulted similar between seasons (WIC = 0.74—0.67; in Autumn and Spring respectively), while the Between Individual Component (BIC) decreases from Autumn to Spring (BIC = 0.42—0.15; in Autumn and Spring, respectively). The value of the ratio WIC/TNW is lower in Autumn (0.63) than in Spring (0.81), and in both season it’s statistically significant (Monte Carlo resampling; p = 0.001) (Fig. 3). The population has been divided into two groups at the proportional similarity index (PSi) value 0.73 in autumn and 0.87 in spring; obtaining two sub-groups on the basis on the individual specialization (48 and 72 individuals in Autumn; 33 and 34 individuals in Spring). In Autumn individuals with low values of PSi had significantly lower values of SMI (Mann Withney; U = 1159, p < 0.001) while during Spring the two groups had similar values (Mann Withney; U = 438, P = 0.12). SVL did not differ significantly between groups in both seasons. The diet of groups characterized by low values of PSi had significantly higher diversity (Mann-Withney; U = 1255, p = 0.006 in Autumn; U = 260, p < 0.001 in Spring) and evenness (Mann-Withney; U = 1084, p < 0.001 in Autumn; U = 220, p < 0.001 in Spring). At the same time the “low PSi” groups accounted for a smaller FORI (Mann-Withney; U = 380, p < 0.001 in Autumn; U = 180, p < 0.001 in Spring) and showed a lower relative abundance of Collembola in their stomachs (Mann-Withney; U = 702, p < 0.001 in Autumn; U = 245, p = 0.002 in Spring) in both seasons. Complete data for the aforementioned analyses, including means and standard deviations of the two subgroups, are presented in Table 2.


Generalisation within specialization: inter-individual diet variation in the only specialized salamander in the world.

Costa A, Salvidio S, Posillico M, Matteucci G, De Cinti B, Romano A - Sci Rep (2015)

Histograms of distributions of within-individual component/trophic niche width (WIC/TNW) ratio and individual specialization (IS) indices obtained by Monte Carlo resampling procedure, both for autumn and spring data.Vertical broken lines show the 95% confidence limits of the simulated distribution, while the vertical solid line shows the actual index value for the original data.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4543951&req=5

f3: Histograms of distributions of within-individual component/trophic niche width (WIC/TNW) ratio and individual specialization (IS) indices obtained by Monte Carlo resampling procedure, both for autumn and spring data.Vertical broken lines show the 95% confidence limits of the simulated distribution, while the vertical solid line shows the actual index value for the original data.
Mentions: The Total Niche Width (TNW) of the population in Autumn is wider than in Spring (TNW = 1.16—0.83; in Autumn and Spring, respectively). The Within Individual Component of the trophic niche (WIC) resulted similar between seasons (WIC = 0.74—0.67; in Autumn and Spring respectively), while the Between Individual Component (BIC) decreases from Autumn to Spring (BIC = 0.42—0.15; in Autumn and Spring, respectively). The value of the ratio WIC/TNW is lower in Autumn (0.63) than in Spring (0.81), and in both season it’s statistically significant (Monte Carlo resampling; p = 0.001) (Fig. 3). The population has been divided into two groups at the proportional similarity index (PSi) value 0.73 in autumn and 0.87 in spring; obtaining two sub-groups on the basis on the individual specialization (48 and 72 individuals in Autumn; 33 and 34 individuals in Spring). In Autumn individuals with low values of PSi had significantly lower values of SMI (Mann Withney; U = 1159, p < 0.001) while during Spring the two groups had similar values (Mann Withney; U = 438, P = 0.12). SVL did not differ significantly between groups in both seasons. The diet of groups characterized by low values of PSi had significantly higher diversity (Mann-Withney; U = 1255, p = 0.006 in Autumn; U = 260, p < 0.001 in Spring) and evenness (Mann-Withney; U = 1084, p < 0.001 in Autumn; U = 220, p < 0.001 in Spring). At the same time the “low PSi” groups accounted for a smaller FORI (Mann-Withney; U = 380, p < 0.001 in Autumn; U = 180, p < 0.001 in Spring) and showed a lower relative abundance of Collembola in their stomachs (Mann-Withney; U = 702, p < 0.001 in Autumn; U = 245, p = 0.002 in Spring) in both seasons. Complete data for the aforementioned analyses, including means and standard deviations of the two subgroups, are presented in Table 2.

Bottom Line: Our results showed that Salamandrina is highly specialized on Collembola and the more specialized individuals are the better performing ones.Our findings reflects the optimal foraging theory both at population and individual level, since animals in better physiological conditions are able to exploit the most profitable prey, suggesting that the two coexisting strategies are not equivalent.At last this species, feeding on decomposers of litter detritus, could play a key role determining litter retention rate, nutrient cycle and carbon sequestration.

View Article: PubMed Central - PubMed

Affiliation: Consiglio Nazionale delle Ricerche, Istituto di Biologia Agroambientale e Forestale (CNR-IBAF), Area di Ricerca Roma 1, Via Salaria km 29, 300-00015. Monterotondo (RM) (Italy).

ABSTRACT
Specialization is typically inferred at population and species level but in the last decade many authors highlighted this trait at the individual level, finding that generalist populations can be composed by both generalist and specialist individual. Despite hundreds of reported cases of individual specialization there is a complete lack of information on inter-individual diet variation in specialist species. We studied the diet of the Italian endemic Spectacled Salamander (Salamandrina perspicillata), in a temperate forest ecosystem, to disclose the realised trophic niche, prey selection strategy in function of phenotypic variation and inter-individual diet variation. Our results showed that Salamandrina is highly specialized on Collembola and the more specialized individuals are the better performing ones. Analyses of inter-individual diet variation showed that a subset of animals exhibited a broader trophic niche, adopting different foraging strategies. Our findings reflects the optimal foraging theory both at population and individual level, since animals in better physiological conditions are able to exploit the most profitable prey, suggesting that the two coexisting strategies are not equivalent. At last this species, feeding on decomposers of litter detritus, could play a key role determining litter retention rate, nutrient cycle and carbon sequestration.

No MeSH data available.


Related in: MedlinePlus