Carnivory evidence for harvesters in Belize based on stable nitrogen isotopes and fecal samples

Abstract

The harvesters are generally considered omnivorous. Unlike most of the other arachnids that are fluid feeders, harvest men are able to eat solid food particles and can consume invertebrates, small vertebrates, plant tissues, fungi and debris. However, for most species, quantitative diet data is missing. The stable nitrogen isotope analysis provides a means to measure the contribution of these materials to the diet during the tissue replacement time scale and, therefore, quantify the trophic position. The fecal material exam can provide additional evidence of recent food, which can further complement field observations and isotopic analysis. We investigate the diet of Erginulus clocvotibial (FO Pickard-Cambridge, 1905) (Arachnida, Opilions, Cosmetidae) in the West of Belize, using analysis of stable isotopes and electronic microscopy of scanning scan of fecal samples. We also examine the isotopic nitrogen relationships for carnivores (scorpions and spiders), herbivores (grasshopper and katydids) and preliminary measures for two other species of harvesters, ants and termites. Erginulus clavotibialis had firms δ15n similar to scorpions and spiders, which indicates Carnivoria. The nymphs and adults (females and males) of E. clavotibialis did not differ significantly at their trophic level despite possessing chelicra and pedipalpos that differ substantially in the size and relative morphology. The fecal samples contained considerable evidence of arthropod consumption, since the fragments of the legs and the exoskeleton were evident. Our study provides an initial quantification of the harvest diet and documents that E. clavotibialis is mainly carnivore.