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Individuals in food webs: the relationships between trophic position, omnivory and among-individual diet variation.

Svanbäck R, Quevedo M, Olsson J, Eklöv P - Oecologia (2015)

Bottom Line: Yet, little is known about its variation among trophic levels and how such variation could affect phenotypic divergence within populations.Third, we test potential evolutionary implications of population trophic position by assessing the relationship between the proportion of piscivorous perch (populations of higher trophic position) and the degree of phenotypic divergence between littoral and pelagic perch sub-populations.We also found that phenotypic divergence was negatively related to trophic position in a population.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Genetics/Limnology, Uppsala University, Norbyvägen 18D, 752 36, Uppsala, Sweden, richard.svanback@ebc.uu.se.

ABSTRACT
Among-individual diet variation is common in natural populations and may occur at any trophic level within a food web. Yet, little is known about its variation among trophic levels and how such variation could affect phenotypic divergence within populations. In this study we investigate the relationships between trophic position (the population's range and average) and among-individual diet variation. We test for diet variation among individuals and across size classes of Eurasian perch (Perca fluviatilis), a widespread predatory freshwater fish that undergoes ontogenetic niche shifts. Second, we investigate among-individual diet variation within fish and invertebrate populations in two different lake communities using stable isotopes. Third, we test potential evolutionary implications of population trophic position by assessing the relationship between the proportion of piscivorous perch (populations of higher trophic position) and the degree of phenotypic divergence between littoral and pelagic perch sub-populations. We show that among-individual diet variation is highest at intermediate trophic positions, and that this high degree of among-individual variation likely causes an increase in the range of trophic positions among individuals. We also found that phenotypic divergence was negatively related to trophic position in a population. This study thus shows that trophic position is related to and may be important for among-individual diet variation as well as to phenotypic divergence within populations.

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Organization of species in the trophic position–littoral reliance plane. Littoral reliance is the average proportion of carbon that comes from the littoral food chain, i.e., if littoral reliance is 0 then the population is feeding 100 % from the pelagic food chain whereas a littoral reliance of 1 means that the population is feeding 100 % from the littoral food chain. Each dot represents the average of a species from Lake Lötsjön (red symbols) and Lake Långsjön (black symbols). See Table S2 for sample sizes
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Fig2: Organization of species in the trophic position–littoral reliance plane. Littoral reliance is the average proportion of carbon that comes from the littoral food chain, i.e., if littoral reliance is 0 then the population is feeding 100 % from the pelagic food chain whereas a littoral reliance of 1 means that the population is feeding 100 % from the littoral food chain. Each dot represents the average of a species from Lake Lötsjön (red symbols) and Lake Långsjön (black symbols). See Table S2 for sample sizes

Mentions: In both Lake Lötsjön and Lake Långsjön, lower trophic level species (invertebrates) tended to be on average either more littoral or more pelagic in their habitat use. Higher trophic level species (fish), on the other hand, tended to be more intermediate in using both littoral and pelagic food resources (Fig. 2; Table S2, appendix). When comparing among populations, trophic position showed a quadratic relationship in diet variation among individuals, measured as average distance to the centroid () of isotopic values; species at intermediate trophic positions had the highest degrees of among-individual diet variation (Fig. 3a; Table 3). There were no differences in this pattern between the lakes (Table 3).Fig. 2


Individuals in food webs: the relationships between trophic position, omnivory and among-individual diet variation.

Svanbäck R, Quevedo M, Olsson J, Eklöv P - Oecologia (2015)

Organization of species in the trophic position–littoral reliance plane. Littoral reliance is the average proportion of carbon that comes from the littoral food chain, i.e., if littoral reliance is 0 then the population is feeding 100 % from the pelagic food chain whereas a littoral reliance of 1 means that the population is feeding 100 % from the littoral food chain. Each dot represents the average of a species from Lake Lötsjön (red symbols) and Lake Långsjön (black symbols). See Table S2 for sample sizes
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4555210&req=5

Fig2: Organization of species in the trophic position–littoral reliance plane. Littoral reliance is the average proportion of carbon that comes from the littoral food chain, i.e., if littoral reliance is 0 then the population is feeding 100 % from the pelagic food chain whereas a littoral reliance of 1 means that the population is feeding 100 % from the littoral food chain. Each dot represents the average of a species from Lake Lötsjön (red symbols) and Lake Långsjön (black symbols). See Table S2 for sample sizes
Mentions: In both Lake Lötsjön and Lake Långsjön, lower trophic level species (invertebrates) tended to be on average either more littoral or more pelagic in their habitat use. Higher trophic level species (fish), on the other hand, tended to be more intermediate in using both littoral and pelagic food resources (Fig. 2; Table S2, appendix). When comparing among populations, trophic position showed a quadratic relationship in diet variation among individuals, measured as average distance to the centroid () of isotopic values; species at intermediate trophic positions had the highest degrees of among-individual diet variation (Fig. 3a; Table 3). There were no differences in this pattern between the lakes (Table 3).Fig. 2

Bottom Line: Yet, little is known about its variation among trophic levels and how such variation could affect phenotypic divergence within populations.Third, we test potential evolutionary implications of population trophic position by assessing the relationship between the proportion of piscivorous perch (populations of higher trophic position) and the degree of phenotypic divergence between littoral and pelagic perch sub-populations.We also found that phenotypic divergence was negatively related to trophic position in a population.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Genetics/Limnology, Uppsala University, Norbyvägen 18D, 752 36, Uppsala, Sweden, richard.svanback@ebc.uu.se.

ABSTRACT
Among-individual diet variation is common in natural populations and may occur at any trophic level within a food web. Yet, little is known about its variation among trophic levels and how such variation could affect phenotypic divergence within populations. In this study we investigate the relationships between trophic position (the population's range and average) and among-individual diet variation. We test for diet variation among individuals and across size classes of Eurasian perch (Perca fluviatilis), a widespread predatory freshwater fish that undergoes ontogenetic niche shifts. Second, we investigate among-individual diet variation within fish and invertebrate populations in two different lake communities using stable isotopes. Third, we test potential evolutionary implications of population trophic position by assessing the relationship between the proportion of piscivorous perch (populations of higher trophic position) and the degree of phenotypic divergence between littoral and pelagic perch sub-populations. We show that among-individual diet variation is highest at intermediate trophic positions, and that this high degree of among-individual variation likely causes an increase in the range of trophic positions among individuals. We also found that phenotypic divergence was negatively related to trophic position in a population. This study thus shows that trophic position is related to and may be important for among-individual diet variation as well as to phenotypic divergence within populations.

Show MeSH