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).