Consequences of species grouping for food web structure

Abstract

Effects of trophic species aggregation on the structural properties of food webs in six Mediterranean streams were assessed here. In each stream, we created three different variations of the original food web, according to the trophic species aggregation applied. The aggregations used here were based on predator-prey relationships, i.e., species were lumped at different levels of trophic habits in the food web into top (T), intermediate (I) and basal (B) species. In our studied food webs, these species corresponded to fishes, macroinvertebrates and different types of detritus, respectively. No significant differences were found in structural properties when we analyzed the stream effect, but these were found in the analysis of aggregation variation effect. Species grouping, and the level within the food web at which it occurs, influenced the structural properties of the food web. However, these properties were comparable between all the studied streams when the same resolution was considered. The relationship between omnivory and connectance was not affected by trophic species grouping. These properties were positively and significantly related in all aggregation variations of the food webs, suggesting that the stabilizing role of omnivory is maintained regardless of the particular grouping method utilized. © 2012, ALÖKI Kft., Budapest, Hungary.