Multiple factors, including arena size, shape the functional responses of ladybird beetles

Abstract

Functional response studies are often used to determine the suitability of predators as biocontrol agents. Ladybird beetles (Coleoptera: Coccinellidae) are often used for the control of crop pests such as aphids. However, most functional response studies on coccinellids compare a limited number of species at different life stages, temperatures or sexes. A large‐scale comparison of ladybird beetle functional responses is needed to evaluate the utility of these species as potential biocontrol predators and to understand the traits that influence the interaction strength between ladybird beetles and their prey. We compiled 158 ladybird beetle functional responses from 30 studies and tested for effects of taxa, traits, temperature and arena size on functional response parameters using linear mixed‐effects models. Our results show that functional response parameters (handling time and space clearance rate) are affected by predator stage, predator mass, prey type, temperature and arena size. Although complicated by interaction terms, space clearance rate generally increased with predator size, temperature and predator stage, while handling time decreased with predator size, temperature and predator stage. Coleopteran prey induced the highest handling times. Our results also show that experimental arena size has a large, consistent effect on space clearance rate. Arena size is more important in determining foraging rates at low prey densities than any other factor considered here, including predator mass and temperature. Efforts to use laboratory‐based functional response experiments to evaluate the efficacy of biocontrol predators are therefore confounded by the choice of arena size. Synthesis and applications. In addition to confirming known body mass and temperature effects, our study reveals previously unclear age‐related effects and the importance of prey types, which can be used to optimize biocontrol programmes. The arena size effect is unexpected and problematic because failure to account for arena size precludes accurate comparison of biocontrol predator effectiveness. We suggest managers and biocontrol practitioners re‐evaluate the efficacy of candidate biocontrol predators, perhaps by statistically controlling for arena size to minimize the influence of this widely unconsidered factor on functional response estimates.

Temperature and prey density jointly influence trophic and non‐trophic interactions in multiple predator communities

“…Our results are consistent with previous meta‐analyses by Rall et al. () and Kalinoski & DeLong (), and the study by Uiterwaal and Delong () showing that the attack rate is more sensitive to warming than handling time. The latter parameter involves a suite of processes such as handling, ingesting, and digesting the prey (Jeschke, Kopp, & Tollrian, ; Sentis, Hemptinne, & Brodeur, ).…”

Trade‐offs between morphology and thermal niches mediate adaptation in response to competing selective pressures

“…Because species interactions are temperature‐dependent (Englund, Öhlund, Hein, & Diehl, ; Uiterwaal & DeLong, ), predation and parasitism also can change the shape of TPCs (Grigaltchik, Ward, & Seebacher, ; Grigaltchik, Webb, & Seebacher, ). For example, populations of Paramecium aurelia exposed to predation show a more rapid increase in growth as temperature increases and a more rapid decline as temperatures decrease than populations not exposed to predation (Luhring & DeLong, ).…”

“…Because species interactions are temperature-dependent (Englund, Öhlund, Hein, & Diehl, 2011;Uiterwaal & DeLong, 2018), predation and parasitism also can change the shape of TPCs (Grigaltchik, Ward, & Seebacher, 2012;Grigaltchik, Webb, & Seebacher, 2016).…”

What drives interaction strengths in complex food webs? A test with feeding rates of a generalist stream predator

“…Predator functional responses, for instance, have been largely based on laboratory experiments and have seen less validation in natural food webs. Artificial effects of the laboratory environment, including experimental duration (Li et al 2018), the size of the arena used for feeding trials (Uiterwaal and DeLong 2018), or unrealistic community structure (e.g., low prey richness, Novak et al 2017) have potential to strongly influence predator feeding rates. Additionally, scaling laws based on temperature and body mass have been applied to infer interaction strengths in food webs, despite sometimes equivocal support for the generality of their predictions (Wootton andEmmerson 2005, Rall et al 2012).…”

“…Limitations of prior work include a focus on one or two hypothesized drivers of interaction strength variation in isolation, and perhaps most importantly, the reliance on experiments entailing oversimplified community structures (e.g., low prey diversity) and unnatural environmental conditions (e.g., laboratory and mesocosm trials; Carpenter 1996). For instance, factors associated with study design, such as experimental duration, the size of the feeding arena, and the hunger level of predators prior to feeding trials can have strong effects on observed predator feeding rates or functional response parameters (Li et al 2018, Uiterwaal andDeLong 2018). The large number of interactions occurring in complex food webs also makes experiments that manipulate the abundance or presence of species intractable.…”