Temperature-dependent consumer-resource dynamics: A coupled structured model for Gammarus pulex (L.) and leaf litter

The annual variation in population density of the stream macroinvertebrate Gammarus pulex is frequently linked to annual courses of both, resource availability and temperature, which is calling for a mechanistic analysis of the system. To this effect, we coupled a size structured population model for the consumer and a quality structured resource model for its main resource, leaf litter standing stock. We introduced temperature dependence of processes and a lumped internal energy storage for reproduction and energy reallocation. One-year's field data on body length frequencies of G. pulex, in-stream leaf litter standing stock, leaf fall and temperature were used to calibrate the model for parameters not yet determined in independent experiments. The model reproduced the seasonal pattern of both dynamics acceptably. Independently measured feeding rates of G. pulex were used to confirm the simulated relationship between resource and consumer. Such, we revealed the contribution of temperature and food response to changes in population density. Temperature effects of mortality and reproduction roughly concur with each other, while the energy response of reproduction is pivotally distinct. In the face of model application for projection of climate change effects, further attention should particularly be paid to the specific temperature response of G. pulex and to the contribution of non-shredding decomposition (physical abrasion and microbial colonization) to loss of leaf litter standing stock.