ABSTRACT

Denno, R.F., and W.F. Fagan. 2003. Might nitrogen limitation promote omnivory among carnivorous arthropods? Ecology 84 : 2522-2531.

Omnivory is a frequent feeding strategy in terrestrial arthropods, occurring across a diversity of taxa occupying a wide array of habitats. Because omnivory has important consequences for broad areas of theoretical and applied ecology, it is essential to understand those factors that favor its occurrence. Here we address the limiting role of nitrogen in promoting omnivory, not so much from the historical perspective of herbivores supplementing their nutrient-poor plant diet, but by extending the argument to higher trophic levels where predators feed on each other as well as herbivores. Drawing on the historically documented mismatch in nitrogen stoichiometry between herbivores and their host plants (plant C:N >> herbivore C:N), and a recently documented, though smaller, difference in nitrogen content between predators and their herbivore prey (herbivore C:N > predator C:N), we discuss the existence of a trade-off between nutrient quality and quantity that occurs across trophic levels. The existence of this trade-off suggests that arthropod predators, which we show to be frequently nitrogen-limited in nature, can enhance their nitrogen intake by broadening their diet to include nitrogen-rich predators. We conclude by outlining the consequences of this trade-off for the relative balance between dietary specialization and supplementation among consumers, emphasizing the divergent roles that large vs. small stoichiometric mismatches may have had for the evolution of omnivory.