Realism of model ecosystems: an evaluation of physicochemistry and macroinvertebrate assemblages in artificial streams

Ecological realism is an important yet rarely reported feature of model ecosystems. In this case study, we assess the realism of four outdoor artificial stream mesocosms (4 m(2)) bordering a chalk river in southern England. Comparisons of physiochemical conditions and benthic macroinvertebrate assemblages were made between the mesocosm units and the parent water body, a side arm of the River Frome. Physicochemistry of the mesocosm replicates was similar to that of the source stream, with congruent temporal variation evident between the real system and each of the models. The high realism of the mesocosms was explained by the outdoor location and close physical proximity of the array to the source stream, and the short mesocosm residence time of water sourced from the parent feeder system. Mesocosms supported a diverse array of benthic macroinvertebrates (60 families from 14 taxonomic orders), including all macroinvertebrate families in the source stream. Individual mesocosms contained a mean of 89% of source stream biota. We conclude that once-through mesocosms can be satisfactory analogues of natural systems, particularly where model and natural scales overlap.