An experimental framework for quantifying the degree of intraguild predation in omnivorous food webs in the field

Abstract

Intraguild predation (IGP) is common in natural and human‐managed systems and plays a critical role in food web dynamics. Although studies have documented the occurrence of IGP across a wide range of predator taxa, quantitative understanding regarding the degree/intensity of IGP remains lacking. I propose an experimental framework combining controlled feeding trials and stable isotope analysis to quantify the degree of IGP in an omnivorous food web in the field consisting of a top predator, a mesopredator, and a shared prey. The degree of IGP is defined as the proportion (in number) of mesopredators consumed in the total diet (shared prey + mesopredator) of top predators. Feeding trials along with stable isotope analysis are used to construct a standard curve of the relationship between the diet composition of top predator and its nitrogen isotope signatures. The nitrogen isotope signatures of field‐collected top predator individuals are then analyzed and interpolated to the standard curve to estimate the degree of IGP in the field. The proposed framework leverages the strengths of different experimental approaches to study trophic interactions, providing a practical tool for quantifying IGP in a more accurate (controlled feeding trials and standard IGP curve) and realistic (stable isotope analysis of field samples) fashion. The current framework can be further extended to food webs involving more complex interactions (e.g., multiple shared prey) and complemented with other approaches (e.g., molecular gut content analysis) to capture a more complete picture of IGP dynamics in the field.

Pattern of seasonal variation in rates of predation between spider families is temporally stable in a food web with widespread intraguild predation

“…The arthropod food web of leaf litter of the forest floor has proven amenable to manipulations of the detrital resource base, long-term rainfall, spider densities, and densities of other generalist arthropod predators (for recent examples and discussions of earlier related studies, refer to [13, [55][56][57][58][59]). Long-term perturbation experiments will be especially valuable in testing theory when coupled with monitoring of changes in feeding connections between food web nodes across different time scales using rapidly evolving DNA, fatty acid, and stable isotopic techniques [7,60].…”

“…IGP can be “asymmetrical” (a module in which a “top” generalist predator, the IGPredator, preys upon an IGPrey, but not vice-versa); or “reciprocal”, in which the two generalist predators prey upon each other, usually at different intensities. IGP is widespread in nature [ 6 ], but quantitative estimates of IGP in most systems are few [ 7 ], particularly for predaceous arthropods [ 8 ]. Knowledge of changes over time in the pattern of IGP in a food web is even more sparse [ 9 ].…”