Predicting the effects of temperature on food web connectance

Abstract

Few models concern how environmental variables such as temperature affect community structure. Here, we develop a model of how temperature affects food web connectance, a powerful driver of population dynamics and community structure. We use the Arrhenius equation to add temperature dependence of foraging traits to an existing model of food web structure. The model predicts potentially large temperature effects on connectance. Temperature-sensitive food webs exhibit slopes of up to 0.01 units of connectance per 18C change in temperature. This corresponds to changes in diet breadth of one resource item per 28C (assuming a food web containing 50 species). Less sensitive food webs exhibit slopes down to 0.0005, which corresponds to about one resource item per 408C. Relative sizes of the activation energies of attack rate and handling time determine whether warming increases or decreases connectance. Differences in temperature sensitivity are explained by differences between empirical food webs in the body size distributions of organisms. We conclude that models of temperature effects on community structure and dynamics urgently require considerable development, and also more and better empirical data to parameterize and test them.

Climate change in size-structured ecosystems

“…For instance, a negative response of the basal species in the food chain of figure 2 may reflect a direct negative warming effect on the basal or the top species, and a positive response of the top species can be associated with a direct positive warming effect on the top or the basal species (figure 2). Predicting the likelihood and strength of these 'thermal cascades' will depend on our understanding of warming effects on network structure [27] and species interaction strengths [28,29]. In addition to physiological accelerations, warming can have effects on the interaction strengths between species (figure 1: c) driven by digestion, movement, behaviour and encounter rates [30,31].…”

“…While these smaller species are expected to exhibit more rapid population oscillations and lower community stability [75], they will also have different diets, which will likely modify network structure (figure 4b). For instance, by using a temperature-based extension of the allometric diet-breadth model, Petchey et al [27,41] suggest that future networks may be characterized by smaller species with less links, more intra-guild predation and lower trophic levels (figure 4b). These network modifications may have severe implications, as top-down control should be weakened by intraguild predation, which may negatively impact ecosystem functioning [76].…”

Warming and nitrogen affect size structuring and density dependence in a host–parasitoid food web

“…Climate warming is known to alter herbivore population growth [16] in addition to affecting individual body size [17] and metabolic process rates [18], and these changes may combine to affect foodweb interactions through a variety of pathways [19]. Similarly, nitrogen deposition is known to alter plant quality, with cascading effects on herbivore individual fitness and population growth [13].…”

Fit, efficiency, and biology: Some thoughts on judging food web models

“…Specifically, it (i) focused on determinants of connectance; (ii) linked biologically testable mechanisms of individual foraging behaviour to food web structure; and (iii) provided a model that could, in theory, be parameterised independently of the data it aimed to Page 4 of 9 predict. Recently, Petchey et al (2010) have shown how a model founded in the foraging behaviour of individual organisms can be extended to make predictions about the effects of temperature change on aspects of food web structure. These predictions were greatly facilitated by the level of mechanism that was included in the ADBM.…”

“…This type of test would require quantified variation in foraging allometries along the gradient, which would be fed into the model to give predictions of food web structure as a function of environmental conditions (e.g., Petchey et al, 2010). This could be compared to observed variation in food web structure caused by environmental variation.…”