Food web functional responses

Abstract

This article reviews the nature of functional responses that have commonly been used to represent feeding relationships in the ecological literature. It compares these with the range of functional response forms that are likely to characterize species in natural communities. The latter set of responses involves many more variables. The article reviews the history of functional response models, and examines previous work that has allowed the functional response of a predator to a single type of prey to depend on additional variables beyond the abundance of that prey type. While a number of more complex functional responses have been discussed over the years, many variables affecting feeding rates are still typically omitted from models of food webs. The influences on functional responses from trophic levels above that of the predator or below that of the prey are particularly likely to be ignored, although models and data have suggested that they can have large effects on the functional response. The influences of adaptive behavior and of the time-scale of response measurement are also too often ignored. Some of the known and unknown consequences of these omissions are discussed.

Predator-mediated interactions through changes in predator home range size can lead to local prey exclusion

“…Theoretical studies have shown that variations in the shape of the functional response can have important ecological consequences for the structure and dynamics of communities by altering the coexistence among prey, and the strength and signs of the interactions among them (Abrams and Cortez, 2015; Abrams et al, 1998; Abrams and Matsuda, 2004; Brose et al, 2006; Coblentz, 2020). However, very few empirically-based multi-species functional responses were developed (Abrams, 2022; DeLong, 2021). The evaluation of functional response using phenomenological models often fail to discriminate between different response shapes (Novak and Stouffer, 2020), which makes it difficult to quantify the strength of predator-mediated interactions in the wild.…”

“…As pointed out by Abrams (2022), our understanding of numerical responses is much more limited than functional responses. To date, the numerical response is typically modeled through demographic processes in classical models (see MacArthur-Rosenzweig equations; Rosenzweig and MacArthur 1963).…”

“…The balance between such opposing indirect effects has been well studied theoretically (Abrams and Matsuda, 1996) but theoretical predictions have rarely been tested in natural communities. This is in part due to difficulties in obtaining empirically based multi-species functional response models (Abrams, 2022; DeLong, 2021) and in being able to measure the relative effects of the predator’s functional and numerical response on the net interaction strength. Process-based mechanistic models (hereafter referred to as mechanistic models) can allow us to disentangle the relative strength of the functional and numerical response of predators, and ultimately improve our ability to accurately quantify the strength of the net indirect interactions in ecological communities (Beardsell et al, 2022; Wootton et al, 2021).…”

“…An increase in prey densities may result in higher predator density through behavioral or demographic processes. In most predator-prey models, the numerical response of a predator is incorporated through reproduction and survival parameters (Abrams, 2022; Courchamp et al, 2003; Rosenzweig and MacArthur, 1963; Serrouya et al, 2015). Although a change in prey density is likely to influence the predator density via reproduction or survival, changes in predator behavior can also lead to marked changes in predator density.…”

Incorporating neurological and behavioral mechanisms of sociality into predator-prey models

“…Extensive work in behavioral ecology and neuroscience challenges this theoretic assumption. Taking behavioral mechanisms, like the following, into account will increase the accuracy of predator-prey models (Lima, 2002;Hacini et al, 2021;Abrams, 2022Abrams, ). 10.3389/fnbeh.2023…”