The Importance of Temporal Resolution in Food Web Analysis: Evidence from a Detritus‐Based Stream

Abstract

A series of time-specific food webs for the macroinvertebrate riffle community of Duffin Creek, Ontario was constructed using dietary information obtained from the analysis of gut contents. Trophic links were quantified using a dietary index of relative importance. Precision of the analysis was maintained at a high level by: (1) identifying dietary items as accurately as possible via direct gut analysis; (2) identifying web members to the species level, thus avoiding the taxonomic aggregation and lumping of size classes common in food web analyses; and (3) ensuring temporal resolution of the web by determining ontogenic variation in the diets of dominant members of the community.The Duffin Creek webs are heavily detritus-based with a large proportion of top-to-basal, and intermediate-to-basal links. Top-to-basal links, proportions of top and intermediate species, and lower connectance (0.180-0.219) varied temporally. Trophic connectance ranged from 0.090 to 0.109, consistent with values expected for a web consisting largely of specialist feeders. Weak links made up the largest proportion of total links in the webs, whereas very strong links made up the smallest proportion. Omnivory was more common than indicated in other webs and can be attributed to ontogenic diet switching.Comparison of the statistics for a summary web with those generated for the time-specific webs indicated that the total number of links per web, total number of species, number of top and intermediate species, and linkage density were much greater for the summary web. In view of these differences, the importance of temporal resolution when assessing food web structure and dynamics is emphasized. The possibility that some of the observed features in our web are common to other detritus-based webs is considered. Future studies of this calibre are justified.

Food web of macroinvertebrate community in a Yangtze shallow lake: trophic basis and pathways

“…As compared our work with relevant studies in streams (e.g. Closs & Lake, 1994;Tavares-Cromar & Williams, 1996;Benke & Wallace, 1997;Schmid-Araya et al, 2002) and ponds (Warren, 1989), many of the patterns in Lake Biandantang are consistent with that in other freshwater benthic systems. These patterns may be summarized as: great importance of detrital base, obvious seasonal shifts in abundance and biomass of consumers and high levels of omnivory in the webs.…”

“…Lake Biandantang is a typical macrophytic lake, through which our study might have shed some light on the trophic puzzle in that kind of lakes. Like other freshwater food web researches (Warren, 1989;Closs & Lake, 1994;Tavares-Cromar & Williams, 1996;Thompson & Townsend, 2003), our results demonstrate that the key basal resource of benthic food web of Lake Biandantang is detritus, and the majority of macroinvertebrates in benthic community of that water are detritivorous species. The origin and function of detritus are worthy of remark.…”

“…However, food webs are not only complex (Hall & Raffaelli, 1991;Williams & Martinez, 2000;Jones & Waldron, 2003), but hardly a static entity. Previous studies have shown that the temporal variations of webs are considerable (Warren, 1989;Closs & Lake, 1994;Tavares-Cromar & Williams, 1996;Schmid-Araya et al, 2002;Froneman, 2004). A good understanding of web patterns requires integrating most dynamics into food web studies.…”

The impact of nonlinear functional responses on the long-term evolution of food web structure

“…There has been an increasing realisation that food webs have a large proportion of weak links (Paine, 1992;Tavares-Cromar & Williams, 1996;Berlow et al, 1999;Neutel et al, 2002), and that weak links tend to stabilise population dynamics (McCann et al, 1998). For this reason, we evaluated the link strength distribution in our model webs.…”

Food webs: reconciling the structure and function of biodiversity

“…Several studies have shown that intra-annual temporal variability alters food-web structure [55,56], but the interaction between temporal variability and ecosystem functions remains unclear. Because organisms at higher trophic levels tend to be larger and longer-lived, the temporal scale of response becomes longer as we move up food webs.…”