Simulating allometric trophic networks
Species traits and specifically body-mass determine ecological processes in natural ecosystems (Brown et al. 2004), including trophic interactions (Brose et al. 2019) and their strengths (Rall et al. 2012). Based on such allometric relationships, an allometric-trophic-network model can simulate the complex dynamics of ecosystems in a controlled environment (Schneider et al. 2016). It defines trophic interactions between different species based on their body-mass ratios and utilizes a set of differential equations that describes density changes over time for two limiting resources, and varying numbers of producers and animal consumers (see Supplementary 1 for a detailed model description). For animals, densities increase with feeding on other animals or producers. The strength of those trophic relationships is determined by feeding rates that comprise capture coefficients, handling times, interference competition, functional responses, and the number of prey species. Producers increase their densities due to growth that is limited by resource availabilities. Densities of animals and producers decrease as they are consumed and due to metabolic demands. Resource densities decrease due to growth of producer species and increase based on refresh rates that assume a constant resource turnover. In comparison to its original formulation (Schneider et al. 2016), we improved the model by updating capture coefficients to depend on the feeding preferences of the interacting species (i.e., carnivorous, omnivorous, herbivorous, autotrophic; Hirt et al. 2017). Further, we used a functional response that shifts from type II to type III as predator-prey body-mass ratios increase (Kalinkat et al. 2013). Throughout the model, we updated scaling coefficients based on empirical results (Ehnes et al. 2011; Lang et al. 2017).