The deadly effects of “nonlethal” predators

Abstract

Abstract. Nonconsumptive predator effects are widespread and include plasticity as well as general stress responses. Caged predators are often used to estimate nonconsumptive effects, and numerous studies have focused on the larval stages of animals with complex life cycles. However, few of these studies test whether nonconsumptive predator effects, including stress responses, are exclusively sublethal. Nor have they assessed whether these effects extend beyond the larval stage, affecting success during stressful life-history transitions such as metamorphosis. We conducted experiments with larvae of a dragonfly (Leucorrhinia intacta) that exhibits predator-induced plasticity to assess whether the mere presence of predators affects larval survivorship, metamorphosis, and adult body size. Larvae exposed to caged predators with no ability to attack them had higher levels of mortality. In the second experiment, larvae reared with caged predators had higher rates of metamorphic failure, but there was no effect on adult body size. Our results suggest that stress responses induced by exposure to predator cues increase the vulnerability of prey to other mortality factors, and that mere exposure to predators can result in significant increases in mortality.

Predators inhibit brain cell proliferation in natural populations of electric fish, Brachyhypopomus occidentalis

“…We found that variation in forebrain cell proliferation in B. occidentalis correlated closely with predation pressure when examined both across all streams and in comparisons within drainages. Moreover, the relationship between [40,41]. In addition, direct, injurious encounters with predators are associated with reduction in brain cell proliferation (table 2).…”

“…Regenerative processes in other animals are energy-intensive [41]. It is possible that, in B. occidentalis, the production of brain cells slows as a consequence of the fish redirecting energy to the production of tail cells.…”

Conspecific density affects predator‐induced prey phenotypic plasticity

“…Predator-induced plastic responses have been shown to affect a wide range of prey phenotypes, ranging from morphological (Relyea 2001), behavioral (Sih et al 2004), physiological (Pangle et al 2007) and prey life history traits (McCauley et al 2011). In general, these phenotypic responses are involved in anti-predator defense, with key ecological consequences from individuals to ecosystems , Hawlena and Schmitz 2010, Guariento and Esteves 2013.…”

Consumptive and nonconsumptive effect ratios depend on interaction between plant quality and hunting behavior of omnivorous predators

“…Nonconsumptive effects can have far‐reaching impacts on trophic cascades (Beckerman, Uriarte, & Schmitz, 1997; Trussell, Ewanchuk, & Bertness, 2003), ecosystem functions (Matassa & Trussell, 2011; Schmitz, Grabowski, & Peckarsky, 2008), and often equal or exceed the effects of consumption (Preisser, Bolnick, & Benard, 2005; Schmitz, Krivan, & Ovadia, 2004). Nonconsumptive effects can increase prey vulnerability to other mortality factors (McCauley & Rowe, 2011) or generate physiological stress, resulting in energetic costs with a cascading negative impact on prey reproduction (Creel, Winnie, & Christianson, 2009; Nelson, 2007; Nelson, Matthews, & Rosenheim, 2004). Lower reproduction due to predators caused by, for example, mating interruption (Travers & Sih, 1991), higher conspicuousness of males attracting females (Uzendoski, Maksymovitch, & Verrell, 1993), or changes in prey behavior that result in lower weight gain or poorer provisioning of progeny (Harfenist & Ydenberg, 1995) should represent the strongest nonconsumptive effects as they reduce prey fitness.…”