Nitrogen in Insects: Implications for Trophic Complexity and Species Diversification

Abstract

Disparities in nutrient content (nitrogen and phosphorus) between herbivores and their plant resources have lately proven to have major consequences for herbivore success, consumer-driven nutrient cycling, and the fate of primary production in ecosystems. Here we extend these findings by examining patterns of nutrient content between animals at higher trophic levels, specifically between insect herbivores and predators. Using a recently compiled database on insect nutrient content, we found that predators exhibit on average 15% greater nitrogen content than herbivores. This difference persists after accounting for variation from phylogeny and allometry. Among herbivorous insects, we also found evidence that recently derived lineages (e.g., herbivorous Diptera and Lepidoptera) have, on a relative basis, 15%-25% less body nitrogen than more ancient herbivore lineages (e.g., herbivorous Orthoptera and Hemiptera). We elaborate several testable hypotheses for the origin of differences in nitrogen content between trophic levels and among phylogenetic lineages. For example, interspecific variation in insect nitrogen content may be directly traceable to differences in dietary nitrogen (including dilution by gut contents), selected for directly in response to the differential scarcity of dietary nitrogen, or an indirect consequence of adaptation to different feeding habits. From some functional perspectives, the magnitude rather than the source of the interspecific differences in nitrogen content may be most critical. We conclude by discussing the implications of the observed patterns for both the trophic complexity of food webs and the evolutionary radiation of herbivorous insects.

Sex and size matter: ontogenetic patterns of nutrient content of aquatic insects

“…In our study, the only pattern in %C was that taxa with sclerotized or armored integuments had greater mean %C than taxa with membranous integuments (Table 1). The slightly higher %N and low C:N of predators relative to other FFGs in our study also agrees with results of other studies (Fagan et al 2002, Evans-White et al 2005, Hambäck et al 2009). The %C and %N of Tabanus sp.…”

“…Furthermore, growth rates are positively correlated with body %P (Elser et al 1996, Frost and Elser 2002, Weider et al 2005) but negatively correlated with adult invertebrate body size (Woods et al 2004). Phylogeny also may constrain P (Woods et al 2004) and N (Fagan et al 2002) content of invertebrates, independent of ontogeny.…”

Predator‐driven elemental cycling: the impact of predation and risk effects on ecosystem stoichiometry

“…2000; Fagan et al. 2002). Nevertheless, the principles explored in these models could easily be extended to considerations of other important elements such as phosphorus.…”

Diets of Breeding Southwestern Willow Flycatchers in Different Habitats

“…Fagan et al (2002) detected higher N concentrations in insect predators compared with herbivores after adjusting for allometry and phylogeny. They suggested that N contents in diets, being higher in plant-feeding insects than in plants, contribute to higher N concentrations in predators.…”