Carcasses and excrement#
Carcasses and excrement are critical components of litter, soil and animal models but the fastest processes using these resources are carrion feeding and coprophagy by animals. If carcasses and excrement are handled within the soil or litter model, new inputs would only become available to animals at the end of each model update step. To avoid the resulting lags in feeding responses to new carcass and excrement inputs, these resources pools are handled within the animal model.
Each grid cell contains two pools recording carcass and excrement mass along with the nitrogen and phosphorus stoichiometry of each resource. The total mass in each pool is divided into two fractions:
scavengable mass that can be consumed by animals, and
decayed mass that will be added to the soil model at the next time step.
When biomass is added to either pool, the relative allocation to the scavengable fraction is determined by the following equation
where \(d\) is the rate at which the resource decays due to microbial activity and \(s\) is the rate at which animals discover and remove the resource.
Future directions ðŸ”
We currently only have one class of carcasses, but this may well be split into separate size classes at some point in the future.
Both rates \(d\) and \(s\) are currently empirically derived constants. Scavenging rate (\(s\)) could be determined dynamically from the animal model but this would introduce parameterisation complexities that we don’t want to tackle at present. Future extensions could allow the microbial decay rate (\(d\)) to vary environmentally (e.g. with temperature).