Is resolution the solution?: the effect of taxonomic resolution on the calculated properties of three stream food webs

1. The influence of the level of taxonomic resolution on estimates of food-web properties was studied in three grassland streams in New Zealand. The food webs, each of which contained approximate to 100 species of algae, macroinvertebrates and fish, were progressively aggregated into higher taxonomic groupings and the effect on food-web properties was assessed. Aggregation was also carried out differentially on particular taxonomic groups to mimic the usual approach to taxonomy in stream food-web studies. 2. Of the commonly used food-web properties, mean chain length and linkage complexity varied little with the degree of taxonomic resolution. Estimates of connectance were markedly higher in coarsely resolved (family level) food webs, possibly as a result of a decrease in the number of web elements. 3. Connectance, linkage density, linkage complexity and prey : predator ratios, but not mean chain length, were strongly affected by inconsistency in the level of resolution used among different taxonomic groups within a food web. 4. In order to make meaningful comparisons among food webs a standardised approach to methodology, resolution and effort is needed.