Consumptive and nonconsumptive effect ratios depend on interaction between plant quality and hunting behavior of omnivorous predators. Issue 7 (9th March 2017)

• Record Type: Journal Article
• Authors: Stephan, Jörg G.; Stenberg, Johan A.; Björkman, Christer
• Is Part Of: Ecology and evolution. Volume 7:Issue 7(2017:Apr.)
• Page Start: 2327
• Page End: 2339
• Publication Date: 2017-03-09
• Subjects: antipredator behavior -- biological control -- clutch size frequency distribution -- foraging behavior -- host acceptance -- indirect plant defense -- nonlethal predator effects -- plant suitability -- predator–prey interactions -- trait‐mediated effects; Ecology -- Periodicals; Evolution -- Periodicals; 577.05
• DOI: 10.1002/ece3.2828
• Languages: English
• ISSNs: 2045-7758

Abstract

Summary: Predators not only consume prey but exert nonconsumptive effects in form of scaring, consequently disturbing feeding or reproduction. However, how alternative food sources and hunting mode interactively affect consumptive and nonconsumptive effects with implications for prey fitness have not been addressed, impending functional understanding of such tritrophic interactions. With a herbivorous beetle, two omnivorous predatory bugs (plant sap as alternative food, contrasting hunting modes), and four willow genotypes (contrasting suitability for beetle/omnivore), we investigated direct and indirect effects of plant quality on the beetles key reproductive traits (oviposition rate, clutch size). Using combinations of either or both omnivores on different plant genotypes, we calculated the contribution ofc onsumptive (eggs predated) andn onc onsumptive (fewer eggs laid) effect on beetle fitness, including a prey density‐independent measure (c:nc ratio). We found that larger clutches increase egg survival in presence of the omnivore not immediately consuming all eggs. However, rather than lowering mean, the beetles generally responded with a frequency shift toward smaller clutches. However, female beetles decreased mean and changed clutch size frequency with decreasing plant quality, therefore reducing intraspecific exploitative competition among larvae. More importantly, variation in host plant quality (to omnivore) led to nonconsumptive effects between one‐third and twice as strong as the consumptive effects. Increased egg consumption on plants less suitable to the omnivore may therefore be accompanied by less searching and disturbing the beetle, representing a "cost" to the indirect plant defense in the form of a lower nonconsumptive effect. Many predators are omnivores and altering c:nc ratios (with egg retention as the most direct link to prey fitness) via plant quality and hunting behavior should be fundamental to advance ecological theory and applications. Furthermore, exploring modulation of fitness traits by bottom‐up and top‐down effects will help to explain how and why species aggregate. Abstract : Within a tritrophic system consisting of four willow genotypes, a herbivorous leaf beetle, and two omnivorous predators (plant sap as alternative food) with contrasting hunting behavior, we aimed for a mechanistic understanding of indirect effects of plant quality on prey survival. We found that different combinations of predator hunting mode and host plant quality (to the omnivore) led to nonconsumptive effects ranging from one‐third to twice as strong as the consumptive effects. Less searching and disturbing the prey due to alternative food may therefore represent a "cost" to the indirect plant defense in form of a lower nonconsumptive effect.