Relationships between traits of organisms and the structure of their metacommunities have so far mainly been explored with meta-analyses. We compared metacommunities of a wide variety of aquatic organism groups (12 groups, ranging from bacteria to fish) in the same set of 99 ponds to minimise biases inherent to meta-analyses. In the category of passive dispersers, large-bodied groups showed stronger spatial patterning than small-bodied groups suggesting an increasing impact of dispersal limitation with increasing body size. Metacommunities of organisms with the ability to fly (i.e. insect groups) showed a weaker imprint of dispersal limitation than passive dispersers with similar body size. In contrast, dispersal movements of vertebrate groups (fish and amphibians) seemed to be mainly confined to local connectivity patterns. Our results reveal that body size and dispersal mode are important drivers of metacommunity structure and these traits should therefore be considered when developing a predictive framework for metacommunity dynamics.

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1. Parameters of condition between normal and deformed fourth instar larvae of Chironomus gr. thummi (Kieffer 1911) were compared in four populations: one reference (PE) and two metal‐polluted sites (NP and SCH) in the River Dommel, and one site polluted by domestic sewage and copper in the River Ijse (NEI). 2. The site PE ranked lowest for metal body burdens, deformities, mortalities and emergence duration, while SCH and NEI ranked highest. 3. Deformed and non‐deformed larvae most often did not differ in length and weight ( in situ end‐points for growth); when differences occurred, deformed larvae tended to be smaller. 4. The energy content and dry weights in one population (NEI) were lower in normal larvae than in the weakly deformed ones. The percentage of ash‐free dry weight was lower in deformed larvae of the polluted Dommel sites, compared to the normal ones. 5. The in vitro emergence rate (end‐point for development of fourth instars) for the reference population PE, both in its own sediment and in artificial cellulose substrate, was better than for the other sites. In two populations (NEI, SCH) the development of deformed larvae in their own sediment was slower, with higher mortality, than for the normal larvae. In one population (NP), normal and deformed larvae survived and developed equally well. The emergence rates of the respective populations were similarly ranked when the larvae were raised in an artificial cellulose substrate. 6. Elution peaks of alleged metal‐binding proteins were lower in deformed larvae from SCH and NEI, but higher in deformed larvae from NP, than in normal larvae. 7. A different development rate and mortality of deformed larvae in non‐adapted populations and the possibility of metal adaptation, as in site NP, may modulate the final outcome of deformity frequencies, thus having an impact on the biomarker value of deformities in benthic midge larvae.

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Animals that dwell at different depths in the sediment, are adapted to different respiratory environments . It is possible that animals that occur deep in the sediment have a higher hemoglobin concentration than surfacedwelling animals . To test this hypothesis, hemoglobin concentrations and weights of eight chironomid species that dwell in the littoral zone were measured . High hemoglobin concentration and weight both seemed to contribute to an ability to cope with low oxygen concentrations, and determined the vertical distribution of chironomids in the sediment. A multiple regression equation, including these factors, was derived . It may be used to predict the median depth of occurrence for species that were not included in this study . High sensitivity of small animals to oxygen stress is discussed from a theoretical point of view . 61