PREDICTING DIET COMPOSITION FROM BODY LENGTH IN THE ZOOPLANKTON PREDATOR LEPTODORA-KINDTI

Leptodora kindti and many other species of zooplankton predator range widely throughout temperate-zone lakes, yet these species are rarely i ncluded in size-based studies of food webs. This oversight derives mai nly from a lack of predictive functions that quantify their effects on prey communities. With laboratory experiments I measured the handling time and phosphorus ingestion of L. kindti fed three cladoceran speci es radiolabeled with P-33 as a tracer of dry weight (DW). In general, laboratory results show that predator body length exerts strong influe nce on maximum prey length, on prey handling time (and indirectly pred ation rate), and on prey profitability (expressed as mu g DW ingested time(-1)) in systematic ways that may be useful in predicting predator y effects of L. kindti on natural prey communities. The prey-capturing structure of L. kindti, called the trap basket, constrains the maximu m length of prey that is consumable, and handling times on prey increa se exponentially as prey length approaches the maximum dimensions of t he trap basket. The empirical relationship is given by the following e quation: Handling time = 1/[0.067(Trap basket length/Prey length - 1)( 0.436)]. I use handling time and body length data to evaluate the pred ictive nature of two previously published regression models that relat e L. kindti trap basket length to body length. This note offers a leng th-based approach to analysis of diet composition in L. kindti that wi ll hopefully encourage increased consideration of this species in futu re studies of food webs.