Body size, body size ratio, and prey type influence the functional response of damselfly nymphs

Abstract

Predator-prey interactions play a crucial role in structuring food webs, and the functional response is one way to measure the strength of this interaction. Here, we examine how predator and prey body size affects the functional response of a generalist predator-damselfly nymphs-feeding on three prey types: copepods, Daphnia, and Chydorus. Our results suggest that consumption of copepods is independent of predator body size, while increased predator body size is associated with an increased space clearance rate for Daphnia and a reduced space clearance rate for Chydorus. When considered together, foraging rates on Daphnia and Chydorus (both cladocerans) are consistent with a hump-shaped functional response, with peak foraging rates occurring at an intermediate predator-prey size ratio. Thus, although most food web theory assumes allometric predator-prey links or peaked functional responses at intermediate predator-prey size ratios, our results suggest that both relationships may occur in food webs, in addition to size-independent functional responses.

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

“…Although some laboratory-based experiments use empty arenas and others include vegetative structure, most experiments also vary in the size of the foraging arenas used. The effect of variation in arena size on functional response parameters has previously received minimal attention, with some research suggesting that arena size may play a role in determining space clearance rate (Uiterwaal, Mares, & DeLong, 2017;Yaşar & Özger, 2005a), and others indicating that it is unimportant (van Rijn, Bakker, van der Hoeven, & Sabelis, 2005).…”

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

“…, Klecka and Boukal , Kalinoski and DeLong , Uiterwaal et al. ). Our findings, coupled with prior work, suggest that prey traits beyond body mass are likely a fundamental driver of variation in predator feeding rates.…”

“…Additionally, two of the four lowest feeding rates were on hemipterans and megalopterans, both possessing other forms of defenses that could possibly minimize predation by sculpin (toxins and formidable mandibles, respectively; Merritt et al 2008). The importance of prey traits in driving variation in predator feeding rates has been recognized and quantified in recent laboratory experiments (Rall et al 2011, Klecka and Boukal 2013, Kalinoski and DeLong 2016, Uiterwaal et al 2017). Our findings, coupled with prior work, suggest that prey traits beyond body mass are likely a fundamental driver of variation in predator feeding rates.…”

All ecological models are wrong, but some are useful

“…In their Discussion and Conclusion, Curtsdotter et al. () rightly argue that incorporating traits beyond body size, such as hunting mode (Pawar, Dell, & Savage, ) or prey type (Uiterwaal, Mares, & DeLong, ), could help better capture residual variation in realized interaction strengths. Unfortunately, such approaches may ultimately need about as much data across predator–prey combinations as would explicit parameterization of the functional responses in the first place; that is, following this suggestion may inadvertently send us back to a scenario when a many‐species problem requires a borderline‐infeasible many‐species solution.…”

“…The allometric assumption sidesteps this issue, but can only be stretched so far before itself being confronted by additional data. In their Discussion and Conclusion, Curtsdotter et al (2019) rightly argue that incorporating traits beyond body size, such as hunting mode (Pawar, Dell, & Savage, 2012) or prey type (Uiterwaal, Mares, & DeLong, 2017), could help better capture residual variation in realized interaction strengths.…”