The Importance of Meiofauna in Food Webs: Evidence From an Acid Stream

Abstract

Seasonal food webs were constructed for the whole invertebrate assemblage (meio‐ and macrofauna) inhabiting Broadstone Stream (southeast England). High and uniform taxonomic resolution was applied in a dietary analysis, by resolving the complete benthic community to species, including the meiofauna, protozoa, and algae. Meiofauna accounted for 70% of all species in the summary web and for 73% and 63% of those in the summer/autumn and spring webs, respectively. The web structure changed between summer/autumn and winter/spring, due to differences in species composition. Many stream invertebrates fed on meiofauna and organic matter. Addition of meiofauna to the Broadstone web increased the percentage of intermediate species. Seasonal webs contained between 54 (spring 1997) and 86 (autumn 1996) interactive taxa and 229–378 trophic links. Marked differences in web complexity were found between the summer/autumn and winter/spring periods. Meiofauna accounted for most of the links in the web with a high proportion of intermediate–intermediate links in summer and autumn (0.421–0.440) and also of intermediate–basal links during winter and spring (0.509–0.628). In general, the summary web showed that intermediate species and basal resources were numerically dominant components in this stream. Web connectance rose slightly between summer (0.052) and winter (0.061) and increased further in spring (0.079), coinciding with a reduction in species number. A high fraction of detritivores was combined with omnivorous predators, many of which supplemented their diets with organic matter and, depending on season, with algae and invertebrate eggs. In addition, a wide range of feeding modes was found among meiofaunal species. The diversity of the Broadstone community suggests that the impact of top predators tends to dissipate. A low proportion of top predators in the web was combined with a low mean number of prey items, other than detritus, in their guts (large predators, 1.08–1.26 prey/individual gut; small‐sized tanypods, 2.15–2.32 prey/individual gut). Dietary similarity was highest in autumn and winter 1996, and observed feeding links of the most common predatory species showed low overlap in their diets. The web architecture of this stream is reticulate and complex, and the patterns observed in these seasonal webs differed from previous stream webs, resulting in low connectance, high linkage density, long food chains, and a high proportion of intermediate species and of intermediate–intermediate links. The food web derived from Broadstone Stream clearly demonstrates that the meiofauna increases web complexity and thus, taking into account their functional diversity, may be crucial to the understanding of food web properties and ecosystems processes in streams.

Food Web Structure in a Harsh Glacier-Fed River

“…Decreasing connectance with food web size has been documented previously [83], [84] and seems to hold true across lotic ecosystems. The largest food webs typically had connectance values of <0.10, compared to 0.14–0.19 in the Ödenwinkelkees river (excluding 2006).…”

Grazing and detritivory in 20 stream food webs across a broad pH gradient

“…Inferring feeding links from prior knowledge, as used here when constructing the binary networks, is a common technique in food web research but has been criticised. Some have claimed that inferring links may overestimate diet breadth (Hall and Raffaelli 1997; Raffaelli 2007) but, conversely, reliance only on directly observed links certainly creates the opposite bias because large numbers of guts are needed to characterise fully the diet of each taxon (especially for predators) and, consequently, the trophic network as a whole (Schmid-Araya et al 2002; Raffaelli 2007; Ings et al 2009; but see Woodward et al 2005). Consequently, inferred feeding links were integrated with directly observed data in our study in order to facilitate comparisons among food webs that were constructed in a consistent and standardised manner.…”

Food web structure in a tropical stream ecosystem

“…However, most stream food webs have been constructed with emphasis only upon macroinvertebrates (Closs & Lake 1994;Tavares-Cromar & Williams 1996;Corigliano & Malpassi 1998;Thompson & Townsend 1999). Recently, two studies demonstrated the importance of meiofauna in the structure of a stream food web (Schmid-Araya & Schmid 2000;Schmid-Araya et al 2002a). The inclusion of meiofauna resulted in an increase of web complexity, and consequently caused modifications in the food web patterns.…”

“…1993; Thompson & Townsend 2000). In recent years food webs constructed with a higher taxonomic resolution (Hall & Raffaelli 1991;Martinez 1991;Tavares-Cromar & Williams 1996;Schmid-Araya et al . 2002a) invalidated some earlier generalizations and showed that features such as long food chain and omnivory are common in food web structure.…”

“…In variable systems such as streams, some work showed temporal variation in food web structure (Closs & Lake 1994;Tavares-Cromar & Williams 1996;Carney et al . 1997; Thompson & Townsend 1999;Schmid-Araya et al . 2002a).…”