Quantifying the relative importance of how local (environmental or niche‐based) and regional (dispersal‐related or spatial) processes regulate the assembly of communities has become one of the main research avenues of community ecology. It has been shown that the degree of isolation of local habitats in the landscape may substantially influence the relative role of environmental filtering and dispersal‐related processes in metacommunities. Dendritic stream networks are unique habitats in the landscape, where more isolated upstream sites have been predicted to be primarily structured by environmental variables, while more central mainstem rivers by both environmental and spatial variables (hereafter the network position hypothesis, NPH). However, the NPH has almost exclusively been tested for stream macroinvertebrates, and therefore its predictions warrant confirmation from multiple taxa. We examined the validity of the NPH for benthic diatoms, macrophytes, macroinvertebrates and fish in the Pannon Ecoregion, Hungary. Following the NPH we predicted a clear dominance of environmental over spatial variables in headwaters, and a larger effect of spatial variables in rivers compared to headwaters. We tested these predictions using variance partitioning analyses separately for the different taxa in headwater and in riverine habitats. We found large differences in the explained community variance when the impact of environmental (physical and chemical) and spatial (overland and watercourse distance) variables for various taxa was studied. In general, total explained variance was lower for the more passively dispersing plant taxa than for animal taxa with more active dispersal in both streams and rivers. However, similar to other studies, the total explained variance was low for both headwater streams and rivers. Community structure of diatoms could be best explained by both environmental and spatial variables in streams, whereas their community structure could not be explained by either variable group in rivers. The significance of environmental and spatial variables depended on the distance measure (overland versus watercourse) in the case of macrophytes. Community structure of macroinvertebrates could be explained by environmental variables in streams and by both environmental and spatial variables in rivers. Moreover, variation was explained by different predictors when macroinvertebrate taxa were divided into flying and non‐flying groups, suggesting the importance of dispersal mode in explaining community variation. Finally, community structure of fishes could be explained by both environmental and spatial variables in streams and only by environmental variables in rivers. In conclusion, we found no clear evidence of the NPH in our multi‐taxa comparison. For example, while patterns in macroinvertebrate communities seem to support the NPH, those in fish communities run counter with the predictions of the NPH. This study thus shows that different taxa may behave differently to isolation effects in stream ne...

No abstract

No abstract

27In the last two decades, the invasion of the Amur sleeper (Perccottus glenii Dybowski, 1877) 28 originating from the Far East can be observed in Eastern and Central Europe. Since the Amur 29 sleeper is a non-game fish species, few detailed studies exist on its feeding ecology both in its 30 native and invaded habitats. We examined the seasonal feeding ecology of Amur sleeper in a 31 lentic and in a lotic habitat. Chironomid larvae, zygpoteran larvae, crustaceans and 32 ephemeropteran larvae dominated the diet. No clear differences between the two habitats were 33 found. The diet composition was mainly regulated by the body size that had stronger effect 34 than the habitat and the season. Although fish consumption was uncommon, we anticipate this 35 finding to the structure of the examined populations, in which large bodied individuals were 36 rare. Our study shows that the Amur sleeper may influence several levels (compartments) of 37 the aquatic food web, although the species proved to be an especially important predator of 38 the invertebrate assemblage.

The role of environmental control and spatial structuring may vary depending on dispersal mode within a metacommunity in stream systems. However, as a result of high seasonal variation in environment conditions and phenological features, there might be considerable seasonal changes in the relative importance of structuring factors. The objective of this study was (i) to determine the relative role of structuring factors for aquatic macroinvertebrates with different dispersal mode groups which have seasonal variation in their dispersal capacity and (ii) to disentangle seasonal changes in metacommunity structuring. We sampled 50 stream sites of the Middle Danube Basin (Hungary) in spring and summer. We compared Distance-Decay Relationships between communities of different dispersal groups and distance measures, and then we used variation partitioning analysis and Moran's eigenvector maps based on overland and watercourse distances to reveal structuring processes in both seasons. We found that metacommunities of all dispersal groups were influenced in both seasons mainly by environmental factors with additional impacts of the spatial components. Our findings suggest that metacommunities of taxa with temporally stable dispersal capacity have seasonally stable structuring processes, while the relative importance of structuring factors can vary seasonally in groups with seasonally changing dispersal capacity.

This manuscript is contextually identical with the following published paper: in the metacommunity theory. In this study we evaluate the relative roles of local 24 environmental and landscape filters, spatial constraints and seasonality in organisation of 25 assemblages of Chironomidae (Diptera), a diverse aquatic insect group with winged adults, in 26 an extremely heterogeneous wetland system, Kis-Balaton, Hungary. As expected, local 27 environmental variables explained a substantial proportion of assemblage variance mainly 28 along sediment structure, macrophyte coverage, and decomposing plant matter gradients. 29Considering the narrow spatial range of the study area, pure spatial influence was 30 unexpectedly strong, likely because of the dispersal limitation related to tall terrestrial 31 vegetation patches and mass effect related to the uneven distribution and area of certain 32 microhabitats and their species pools. Whereas landscape-and season-related variability 33 proved to be low or negligible. Taxonomic and functional feeding guild (FFG) based 34 approaches revealed the same main trends in assemblage data; however, FFGs seemed to 35 track environmental changes more tightly. We argue for the common use of taxonomic and 36 functional based approaches, and advise the improvement of species optima and tolerance 37 spectra databases to expand bioassessment power. 38 39

No abstract

No abstract