Connectance in stream food webs

Abstract

Summary1. The properties of food webs are important both in theoretical ecology and environmental management, yet remain elusive. Here, we examined 12 new stream food webs of higher taxonomic resolution and completeness than any previously published data set and combined them with other 10 published stream webs. 2. Compared with most previously published food webs, these stream communities (containing between 22 and 212 species) had more feeding links per species, a higher fraction of intermediate species (0·78-0·88) and lower fractions of top (0·04-0·09) and 'basal' species (0·07-0·15). 3. The exponent of the log link-log species relationship ( S 1·3 ) differed significantly (  : P < 0·001) from the link-species 'law' ( S 1 ) and the constant connectance hypothesis ( S 2 ). Based on these results, the link scaling law and the constant connectance hypothesis must be rejected for food webs in stream systems. 4. Connectance was markedly lower than previously reported and decreased with web size. We attribute this to the body-size disparity of organisms at the top and the bottom of the web, flow disturbance and to the high physical heterogeneity and complexity of the sedimentary habitat. All these may reduce the fraction of possible feeding links that are realized.

Food Web and Trophic Basis of Production of the Benthic Macroinvertebrate Community of a Subtropical Stream (Yangtze River Basin, Middle China)

“…Animal material was only found to be the main food type (14.95%) of an omnivore T. lentiginos. These feeding patterns can be compared to others reported in tropical and temperate streams of Asia, Europe and USA (BENKE and WALLACE, 1980;WALLACE and BENKE, 1984;BRIAND, 1985;WINEMILLER, 1990;LANCASTER and ROBERTSON, 1995;SCHMID-ARAYA et al, 2002b;MANTEL et al, 2004). Detritus plays an important role in stream food webs as the key source of energy and nutrients for macroinvertebrates.…”

Seasonal variation in fish trophic networks in two clear-water streams in the Central Llanos region, Venezuela

“…Connectance values for Charcote and Charcotico were low compared to values reported for other terrestrial and aquatic food webs, some with estimates as high as 4 (Hewatt, 1937;Paine, 1966Paine, , 1980Menge, Sutherland, 1976;Dunne et al, 2002). Schmid-Araya et al (2002) concluded that connectance of stream food webs is lower than in other types of ecosystems. Low connectance of stream food webs may be associated with body size disparity within food chains, disturbance associated with flow variation, and heterogeneity and complexity of stream habitats (Schmid-Araya et al, 2002).…”

“…Schmid-Araya et al (2002) concluded that connectance of stream food webs is lower than in other types of ecosystems. Low connectance of stream food webs may be associated with body size disparity within food chains, disturbance associated with flow variation, and heterogeneity and complexity of stream habitats (Schmid-Araya et al, 2002). Differences between connectance of our trophic networks based on fish diets and connectance values reported in studies that analyzed published food web diagrams could be methodological artifacts; for example, our food webs have many nodes but lack trophic links between invertebrates and their food resources, and most published food web diagrams contain few nodes, with many nodes consisting of highly aggregated taxa or functional groups (Paine, 1988;Winemiller, 1990;Cohen et al, 1993).…”

Disentangling food webs interactions in the littoral of temperate shallow lakes

“…grasslands and rainforest) and aquatic (freshwater and marine) environments suggest that network robustness increases with connectance Thompson et al, 2012). In comparison with surveys conducted by Martinez (1991) in Little Rock Lake (USA) and Schmid-Araya et al (2002b) in different ecosystems across the UK, our biocoenotic analysis was conducted over small spatial distances, within short time periods, and among shallow water bodies with slight habitat differences. The empirical data-sets collected in this study could be used for further food web simulations and could contribute to comparative studies among diverse ecosystem networks (Bascompte, 2009).…”