Use of fatty acid analyses to assess trophic relations of omnivorous larval amphibians

Trophic relationships of omnivores are often difficult to quantify due to the variability of resources consumed.  We examined trophic relationships of three omnivorous larval anurans (Lithobates catesbeiana, L. clamitans, and Pseudacris crucifer) in four southern Illinois ponds using fatty acid analyses.  Single linkage cluster analysis was then used to compare fatty acid profiles among tadpole gut contents, tadpole muscle tissues, and available food resources.  Diets of each species varied among ponds, but organic sediments contributed most to the fatty acid composition of gut contents of all species.  Fatty acid profiles also indicated that larval insects and phytoplankton were consumed by both L. catesbeiana and L. clamitans in one pond, while L. clamitans and P. crucifer consumed mainly periphyton in another pond.  The fatty acid composition of muscle tissues of L. clamitans, the dominant tadpole in these systems, indicated that organic sediments and bacteria were common components of the assimilatory diet.  Analyses revealed variability in diets of each species among ponds and differences between species within each pond, suggesting that there is a high degree of plasticity in the diets of these omnivores.