Predation risk estimated on live and artificial insect prey follows different patterns

Abstract

Models mimicking prey organisms are increasingly used in ecological studies, including testing fundamental ecological and evolutionary theories. The general consensus is that predation risk estimated on artificial models may not quantitatively correspond to predation pressure on live prey, but it still can be used in various comparisons. We tested whether the use of live and artificial prey reveals the same patterns of variation in predation risk. We exposed live prey (blowfly larvae and puparia) and plasticine models of blowfly puparia in two boreal forest sites, both openly and in ant‐ and bird‐exclusion treatments, and we quantified attacks by both avian and invertebrate predators. Bird attack rates were always higher on live puparia than on their plasticine models, but the magnitude of this difference declined from 8.4‐fold in early summer to 2‐fold in mid‐ and late‐summer. We attribute these changes to different responses to prey by experienced adult birds that dominate the bird communities in early summer versus explorative juvenile birds that are abundant later in the season. Invertebrate daily predation rates on maggots decreased from 56% in early summer to 28% in late summer, but invertebrate attacks on plasticine models showed no seasonal changes. Overall, invertebrate predation on maggots was 67‐fold greater than their predation on models. Observations showed that wood ants did not attack plasticine models and did not leave on them any damage marks. Estimates based on artificial prey indicate a much greater role of bird predation than invertebrate predation, while estimates based on live prey suggest the opposite pattern. Thus, using live and artificial prey may lead to different conclusions about relative importance of different predator groups in a locality. Moreover, for both avian and invertebrate predators, predation risk based on artificial and live prey shows different seasonal changes and may potentially demonstrate different spatial patterns.

Decomposing an elevational gradient in predation by insectivorous birds

“…In the case of our predator assay, clay caterpillars are certainly of lower nutritional value to birds. Although the use of clay caterpillars is widespread, the method comes with explicit biases in that the lack of chemical and behavioral cues drives the underestimation of predation rates as compared with live sentinel prey (Nimalrathna et al, 2023; Zvereva & Kozlov, 2023). Even though the intensity of predation is likely underestimated in our study, we believe this method to be as informative of predator behavior as if using real prey, acknowledging that actual predation may be at a higher rate (Lövei & Ferrante, 2017).…”

“…Even though the intensity of predation is likely underestimated in our study, we believe this method to be as informative of predator behavior as if using real prey, acknowledging that actual predation may be at a higher rate (Lövei & Ferrante, 2017). Furthermore, there is evidence that birds respond to response to variation in prey quality in a manner that would result in associational effects; bird attack rates of experimentally deployed blowfly puparia were 8.4‐fold higher than attacks of simultaneously deployed clay models (Zvereva & Kozlov, 2023). Based upon such findings, it can be expected that estimates of predation rate with clay caterpillars are driven not only by the abundance and composition of predator communities—as is commonly assumed—but also by prey communities within which the assay is conducted.…”

“…Where necessary, we pruned leaves around the caterpillars to prevent contact with the clay and replaced caterpillars in the same location following any predator attack. The month of August at our field sites is generally postfledging time for bird communities, which in turn may drive higher rates of predation as naive birds have been shown to increase attack rates due to higher risk taking and unlearned behaviors (Zvereva & Kozlov, 2021, 2023), although this is true for all our field sites and is therefore unbiased. We recorded models attacked by birds four separate times from July 31 to August 13, on day 3 (3 days of deployment), day 5 (2 days of deployment), day 7 (2 days of deployment), and day 14 (7 days of deployment), with the exception of one valley (Taylor River Lower) which was initiated on day 3 and subsequently checked three times.…”

Pest suppression potential varies across 10 bioenergy cropping systems

“…Some predators respond similarly to live and plasticine sentinel prey (Ferrante et al, 2017), but in general, attack rates on plasticine sentinels tend to be lower (Lövei & Ferrante, 2017). Two new studies have also found artificial prey can underestimate attacks by invertebrates more severely than those by vertebrates (Nimalrathna et al, 2023; Zvereva & Kozlov, 2022). Disparities between attack rates on live prey vs. artificial sentinels can also change strongly within a season and do so inconsistently depending on the predator group in question, leading to misleading conclusions about the relative importance of various predator groups.…”

Clay larvae do not accurately measure biogeographic patterns in predation

“…Clay models mimicked the colour (light brown), size (5 cm long × 0.25 cm diameter), and shape (cylinders) of real superworms. While some studies compare predation on real larvae to predation on clay models of a different species (real brown mealworms to green clay caterpillars; Nimalrathna et al, 2023) or life stage (real white maggots to purple clay puparia; Zvereva & Kozlov, 2023), isolating the effect of clay models requires that models mimic the real prey they are being compared with, as the size, shape, and colour of models can F I G U R E 1 Experiment locations and set-up. We measured predation at six sites: a high-elevation alpine site (a) and low-elevation aspen parkland site (b) in Alberta, Canada; a temperate old growth forest in Quebec, Canada (e); a tropical rain forest in Panama (c); a tropical deciduous forest in Colombia (f); and a wet steppe shrubland in Patagonia, Argentina (g; site details in Table 1, map in (d)).…”