Revisiting the Classics: Considering Nonconsumptive Effects in Textbook Examples of Predator–prey Interactions

Abstract

Predator effects on prey dynamics are conventionally studied by measuring changes in prey abundance attributed to consumption by predators. We revisit four classic examples of predator-prey systems often cited in textbooks and incorporate subsequent studies of nonconsumptive effects of predators (NCE), defined as changes in prey traits (e.g., behavior, growth, development) measured on an ecological time scale. Our review revealed that NCE were integral to explaining lynx-hare population dynamics in boreal forests, cascading effects of top predators in Wisconsin lakes, and cascading effects of killer whales and sea otters on kelp forests in nearshore marine habitats. The relative roles of consumption and NCE of wolves on moose and consequent indirect effects on plant communities of Isle Royale depended on climate oscillations. Nonconsumptive effects have not been explicitly tested to explain the link between planktonic alewives and the size structure of the zooplankton, nor have they been invoked to attribute keystone predator status in intertidal communities or elsewhere. We argue that both consumption and intimidation contribute to the total effects of keystone predators, and that characteristics of keystone consumers may differ from those of predators having predominantly NCE. Nonconsumptive effects are often considered as an afterthought to explain observations inconsistent with consumption-based theory. Consequently, NCE with the same sign as consumptive effects may be overlooked, even though they can affect the magnitude, rate, or scale of a prey response to predation and can have important management or conservation implications. Nonconsumptive effects may underlie other classic paradigms in ecology, such as delayed density dependence and predator-mediated prey coexistence. Revisiting classic studies enriches our understanding of predator-prey dynamics and provides compelling rationale for ramping up efforts to consider how NCE affect traditional predator-prey models based on consumption, and to compare the relative magnitude of consumptive and NCE of predators.

Interactive effects of predation risk and conspecific density on the nutrient stoichiometry of prey

“…2004), some classical examples have neglected the role of predation risk on community and ecosystem dynamics (Peckarsky et al. 2008). In addition, very few studies have evaluated the role of predation risk on the physiological traits of prey, such as elemental stoichiometry (Costello and Michel 2013; Dalton and Flecker 2014).…”

Limiting similarity, species packing, and the shape of competition kernels

“…Among the reasons for waste in competition could be individuals that monopolize resources (interference competition), including resources they do not use. Waste could also be a side-effect of so-called trait-mediated interactions, in which individuals restrict their foraging in response to increased predation risk (Peckarsky et al, 2008;Preisser and Bolnick, 2008). Furthermore, if competition is mediated by traits (such as body size) that influence the extent to which species share predators, which is referred to as apparent competition (Holt, 1977), one should not expect the resulting competition kernels to be positive definite.…”

“…Furthermore, if competition is mediated by traits (such as body size) that influence the extent to which species share predators, which is referred to as apparent competition (Holt, 1977), one should not expect the resulting competition kernels to be positive definite. Species interactions through the sharing of predators could be either positive or negative (Abrams and Matsuda, 1996), although effects of trait-mediated interactions (Peckarsky et al, 2008;Preisser and Bolnick, 2008) will often be negative. It has been suggested that apparent competition is quite common in large and diverse groups of organisms, such as phytophagous insects (van Veen et al, 2006).…”

Body condition and pregnancy in northern Yellowstone elk: Evidence for predation risk effects?

“…Despite these criticisms and disparate findings, we encourage continued site-specific investigations of the relative influences of habitat conditions and antipredator responses on the body condition and probability of pregnancy in elk because, theoretically, the consequences of antipredator responses that carry nutritional costs could approach the consequences of direct predation Christianson 2008, Peckarsky et al 2008). Future studies should consider factors in addition to predation that could lower pregnancy rates in elk, including climate and forage conditions (Peckarsky et al 2008), an aging population (White and Garrott 2005), interactions among nutrition, condition, and lactation (Cook et al 2004a, b), low breeding bull : female ratios (Raedeke et al 2002), and diseases such as brucellosis (Geremia et al 2009, Rhyan et al 2009) that are increasing in prevalence in some areas (Cross et al 2010). The Yellowstone wolf saga has become an exemplar of the ecological consequences of large predator restoration, which is likely to guide science and policy regarding such intentional introductions.…”