Abstract
Predators can play an important role in regulating prey abundance and diversity, determining food web structure and function, and contributing to important ecosystem services, including the regulation of agricultural pests and disease vectors. Thus, the ability to predict predator impact on prey is an important goal in ecology. Often, predators of the same species are assumed to be functionally equivalent, despite considerable individual variation in predator traits known to be important for shaping predator–prey interactions, like body size. This assumption may greatly oversimplify our understanding of within-species functional diversity and undermine our ability to predict predator effects on prey. Here, we examine the degree to which predator–prey interactions are functionally homogenous across a natural range of predator body sizes. Specifically, we quantify the size-dependence of the functional response of African clawed frogs (Xenopus laevis) preying on mosquito larvae (Culex pipiens). Three size classes of predators, small (15–30 mm snout-vent length), medium (50–60 mm) and large (105–120 mm), were presented with five densities of prey to determine functional response type and to estimate search efficiency and handling time parameters generated from the models. The results of mesocosm experiments showed that type of functional response of X. laevis changed with size: small predators exhibited a Type II response, while medium and large predators exhibited Type III responses. Functional response data showed an inversely proportional relationship between predator attack rate and predator size. Small and medium predators had highest and lowest handling time, respectively. The change in functional response with the size of predator suggests that predators with overlapping cohorts may have a dynamic impact on prey populations. Therefore, predicting the functional response of a single size-matched predator in an experiment may misrepresent the predator’s potential impact on a prey population.
Highlights
Predator–prey interactions are important in regulating prey populations and determining the structure of aquatic communities (Brooks & Dodson, 1965; Carpenter, Kitchell &How to cite this article Thorp et al (2018), Size-dependent functional response of Xenopus laevis feeding on mosquito larvae
Studies often compare functional responses of native and invasive predators and important inferences are made about the potential impacts of these invaders
Little research focuses on the potential role predator size could play in determining these functional responses
Summary
Predator–prey interactions are important in regulating prey populations and determining the structure of aquatic communities (Brooks & Dodson, 1965; Carpenter, Kitchell &How to cite this article Thorp et al (2018), Size-dependent functional response of Xenopus laevis feeding on mosquito larvae. The few studies that have quantified how predator size influences shapes of functional responses on the same prey have highlighted size-dependence of predator handling time and attack rate (e.g., Eveleigh & Chant, 1981; Vucic-Pestic et al, 2010; Milonas, Kontodimas & Martinou, 2011; Anderson et al, 2016), and even the general form of the functional response (Anderson et al, 2016) These studies show that assuming that predators of the same species are functionally equivalent may greatly oversimplify our understanding of within-species functional diversity and undermine our ability to predict predator effects on prey
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