Abstract. Food webs depict who eats whom in communities. Ecologists have examined statistical metrics and other properties of food webs, but mainly due to the uneven quality of the data, the results have proved controversial. The qualitative data on which those efforts rested treat trophic interactions as present or absent and disregard potentially huge variation in their magnitude, an approach similar to analyzing traffic without differentiating between highways and side roads. More appropriate data are now available and were used here to analyze the relationship between trophic complexity and diversity in 59 quantitative food webs from seven studies (14-202 species) based on recently developed quantitative descriptors. Our results shed new light on food-web structure. First, webs are much simpler when considered quantitatively, and link density exhibits scale invariance or weak dependence on food-web size. Second, the ''constant connectance'' hypothesis is not supported: connectance decreases with web size in both qualitative and quantitative data. Complexity has occupied a central role in the discussion of food-web stability, and we explore the implications for this debate. Our findings indicate that larger webs are more richly endowed with the weak trophic interactions that recent theories show to be responsible for food-web stability.

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Can. Enr. 122: 563-577 (1990) Promoresia elegans (LeConte), Optioservus fastiditus (LeConte), and Stenelmis N. bicarinata LeConte coexist in Duffin Creek, Ont., making up 3.7&23.92% of the riffle fauna present.Promoresia elegans and 0. fastiditus appeared to have semi-voltine life histories. Stenelmis nr. bicarinata appeared to be univoltine but with overlapping generations and slow recruitment occurring from late summer to fall; growth was slow in winter but fast in spring and summer.Based on the index of relative importance (Pinkas et al. 1971), detritus was identified as the most important food source for all size classes and all species throughout the year. Microinorganics ranked second, with diatoms, fungal hyphae, and vascular plant material being the least important food sources. There was no indication of ontogenic food switching in any of the species.The Schoener (1970) niche overlap index indicated almost complete dietary overlap (Cxy = 0.78-0.97) among the three species throughout the year and the Hurlbert (1978) niche overlap index similarly indicated a convergence of diets (L = 1.31-3.54).Niche breadth values were found to be high for all species on the rock surfaces (generalist diet) but were lower in the hyporheic zone indicating a higher degree of specialization there. Tavares, A.F., et D.D. Williams. 1990. Les mktamorphoses, la nutrition et la chevauchure des niches de trois espi?ces sympatriques d'Elmides (Col6operes) d'un ~i s s e a u tempkrk. Can. Ent. 122: 563-577. Resume Promoresia elegans (LeConte), Optioservus fastiditus (LeConte) et Stenelmis N. bicarinata LeConte coexistent i Duffin Creek, Ont., constituant 3,78 i 23,928 de la faune pssente au zone d'ondulation. Promor~sia elegans et 0. fastiditus ont paru d'avoir les m6tamorphoses semivoltines. Stenelmis N. hicmnura a paru d'Ctre d'une metamorphose univoltine, mais ayant des generations chevauchantes et un recrutement lent i partir de tard en Ct6 jusqu'ii I'automne; la croissance a ttC lente en hiver, mais rapide au printemps et ?I I'Cte. Selon I'index d'importance relative (Pinkas et a[. 1971), le detritus a ttt? identifit? comme la source la plus importante d'alimentation dans le cas des insectes dc toutes grandeurs et de toutes espkces, I'annte durant. Les micro-inorganiques ont Ctk en deuxikme place, pendant que les diatomks, les hyphes fongueux, et du mahiel vasculaire des plantes ont 6te parmi les sources les rnoins importantes d'alimentation. Aucune indication de modification d'alimentation ontog6nique n'a CtC observCe de la part de n'importe quelle espkce. L'index de chevauchement des niches de Schoener (1970) a dCmontr6 un chevauchement presque compl2t d'alimentation (Cxy = 0,7R-0,97) parmi les tmis es@ces pendant I'annec et I'index de chevauchement des niches de Hurlbert (1978) a aussi dCmontr6 une convergence d'alimentation (L = 1,3 1-3,54).Les valeurs pour la largeur des niches ont kt6 elevtes en ce qui conceme toutes espkes aux surfaces du rocher (alimentation gCn&raliste), mais plus baws au zone hyporhkique, indiquant ...

1. Chironomid larvae and adults were collected from several freshwater habitats around the Chernobyl site from 1990 to 1994 (4–8 years after a nuclear accident) and examined for morphological deformities. 2. Deformities were found in larvae of nine of the 13 species collected, and were most obvious in headcapsule structures, particularly the antennae, mentum, mandibles and epipharyngeal pectens. 3. In species of Chironomus, the most abundant genus, there was a positive linear relationship between the incidence of deformity and radiation level. Indices of severity of deformity showed similar trends. It is suggested that these deformities resulted largely from ingestion of irradiated, plant‐derived, fine particulate food. 4. Among adult male Ch. riparius, the deformity index decreased both with increasing time from the accident and with increasing distance from the reactor, although these trends were not statistically significant. There was also a trend of increased severity of deformity closer to the accident, both in time and space. 5. Overall, there was a greater incidence of deformity in the larvae than in the adults (e.g. 60 versus 20%, respectively, at the Krasnoselye site and 33 versus 20%, respectively, at the more distant Dron’ki site). 6. It was not possible to determine whether the deformities were inherited from previous generations or were somatic occurrences in each new generation as a consequence of the radiation that continues to pervade the region.