The Role of Relative Body Size in a Predator-Prey Relationship between Dragonfly Naiads and Larval Anurans

Abstract

Size-limited predator-prey systems can be the ecological background for natural selection on prey growth rate and body size. In a laboratory experiment on one such system, individual predatory Tramea lacerata (Odonata: Anisoptera: Libellulidae) naiads of varying sizes were exposed to three densities of Rana areolata (Anura: Ranidae) tadpoles in each of five size classes. Predation rate decreased with increases in tadpole body size. Larger naiads consumed slightly more tadpoles than did smaller naiads when tadpoles were very small, but at larger tadpole sizes, naiad size did not affect the predation rate. Although the number of tadpoles consumed increased with increasing tadpole density, the proportion of the total number that were eaten decreased with increasing density. When tadpoles were very small, naiads that ate more prey grew larger. When tadpoles were larger, there was little variation in the number eaten and no detectable relationship between the number eaten and subsequent naiad growth. These data resolve several paradoxical reports in the literature.