Feeding ecology of granivorous carabid larvae: a stable isotope analysis

Abstract

Although most carabids are primarily carnivorous, some carabid species are omnivorous, with mainly granivorous feeding habits during the larval and/or adult stages (granivorous carabids). This feeding habit has been established based on laboratory and field experiments; however, our knowledge of the feeding ecology of these beetles in the field is limited owing to the lack of an appropriate methodology. In this study, we tested the utility of stable isotope analysis in investigations of the feeding ecology of granivorous carabids in the field, using two closely related syntopic species, Amara chalcites and Amara congrua. We addressed two issues concerning the feeding ecology of granivorous carabids: food niche differentiation between related syntopic species during the larval stage and the effect on adult body size of supplementing seeds with an animal diet during the larval stage. To investigate larval feeding habits, we analysed newly emerged adults, most somatic tissues of which are considered of larval origin. In the two populations examined, both δ15N and δ13C were significantly higher in A. chalcites than A. congrua, suggesting that the two species differentiate food niches, with A. chalcites larvae being more carnivorous than A. congrua larvae. The two isotope ratios of A. chalcites samples from one locality were positively correlated with body size, suggesting that more carnivorous larvae become larger adults. However, this relationship was not detected in other species/locality groups. Thus, our results were inconclusive on the issue of diet supplementation. Nevertheless, overall, these results are comparable with those of previous laboratory‐rearing experiments and demonstrate the potential utility of stable isotope analysis in field studies on the feeding ecology of granivorous carabids.

Laboratory studies on larval food habits of two syntopic, related, granivorous ground beetles Amara chalcites and A. congrua (Coleoptera: Carabidae): a comparison with stable isotope analysis

“…(A.) congrua Morawitz, which are phylogenetically related (Hieke 2003) and have similar characteristics in food habits [omnivorous with a mainly granivorous feeding habit, as both larvae and adults; (Habu and Sadanaga 1961;Ishitani 1996)], body size (Sasakawa et al 2010), and an annual life cycle (Ishitani 1996;Kubota 1998). Despite these similarities, the two species occur syntopically in most areas (Habu 1977;Ishitani 1996;Kubota 1998).…”

“…Despite these similarities, the two species occur syntopically in most areas (Habu 1977;Ishitani 1996;Kubota 1998). Based on these facts, Sasakawa et al (2010) considered that the two species exhibited food-niche differentiation during the larval stage and tested this assumption using stable-isotope analysis. Their results showed, as expected, food-niche differentiation between during the larval stage, with A. chalcites larvae being more carnivorous than A. congrua larvae (Fig.…”

“…In gut-content analysis, because of differential digestion rates among food types, diet composition can be represented only at the population level (i.e., the percentage of individuals from which the focal diet was detected, e.g., Walrant and Loreau 1995;Sunderland et al 1995). With the availability of quantitative estimates of diet compositions for individual samples, it is possible to obtain reliable quantitative data on feeding ecology in the field, such as the difference in food habits among species (Sasakawa et al 2010;Okuzaki et al 2010) and the effects of diet on performance (Sasakawa et al 2010). Importantly, these issues (interspecies difference in food habits and dietary effects on performance) have been studied in many carabids by laboratory-rearing experiments (e.g., Wallin et al 1992;Saska 2005;Fawki and Toft 2005).…”

“…For Carabidae, there have been several studies on temperate species (Sasakawa et al 2010;Okuzaki et al 2010). Compared with gut content analysis, the chief advantage of stable-isotope analysis is that quantitative estimates of diet composition can be performed for each individual sample.…”

“…The authors Fig. 1 Stable isotope analysis of Amara chalcites and A. congrua [data derived from Sasakawa et al (2010)]. Newly emerged adults with soft integuments, the most somatic tissues of which are considered of larval origin (i.e., teneral adults), were analyzed.…”