Body size predicts ontogenetic nitrogen stable-isotope (δ15N) variation, but has little relationship with trophic level in ectotherm vertebrate predators.

Large predators have disproportionate effects on their underlying food webs. Thus, appropriately assigning trophic positions has important conservation implications both for the predators themselves and for their prey. Large-bodied predators are often referred to as apex predators, implying that they are many trophic levels above primary producers. However, theoretical considerations predict both higher and lower trophic position with increasing body size. Nitrogen stable isotope values (δ15N) are increasingly replacing stomach contents or behavioral observations to assess trophic position and it is often assumed that ontogenetic dietary shifts result in higher trophic positions. Intraspecific studies based on δ15N values found a positive relationship between size and inferred trophic position. Here, we use datasets of predatory vertebrate ectotherms (crocodilians, turtles, lizards and fishes) to show that, although there are positive intraspecific relationships between size and δ15N values, relationships between stomach-content-based trophic level (TPdiet) and size are undetectable or negative. As there is usually no single value for 15N trophic discrimination factor (TDF) applicable to a predator species or its prey, estimates of trophic position based on δ15N in ectotherm vertebrates with large size ranges, may be inaccurate and biased. We urge a reconsideration of the sole use of δ15N values to assess trophic position and encourage the combined use of isotopes and stomach contents to assess diet and trophic level.

Primeiro registro de larvas de Chironomus inquinatus Correia, Trivinho-Strixino & Michailova (Diptera, Chironomidae) vivendo no casco do cágado Phrynops geoffroanus Schweigger (Testudines, Chelidae) na região Neotropical / First record of Chironomus inquinatus larvae Correia, Trivinho-Strixino & Michailova (Diptera, Chironomidae) living on the shell of the side-necked turtle Phrynops geoffroanus Schweigger (Testudines, Chelidae)

Neste estudo reportamos pela primeira vez a ocorrência de larvas de Chironomus inquinatus Correia, Trivinho-Strixino & Michailova vivendo no casco do cágado Phrynops geoffroanus Schweigger, possivelmente em função da intensa acumulação de sedimento, em um rio poluído da região Neotropical.

In this study we report for the first time the occurrence of Chironomus inquinatus larvae Correia, Trivinho-Strixino & Michailova living on the shell of the side-necked turtle, Phrynops geoffroanus Schweigger, possibly by the intense accumulation of sediment, in a polluted river of the Neotropics.