Małgorzata Dukowska

Coexistence of fish species in a large lowland river: food niche partitioning between small-sized percids, cyprinids and sticklebacks in submersed macrophytes.

In the spring and summer of each year, large patches of submersed aquatic macrophytes overgrow the bottom of the alluvial Warta River downstream of a large dam reservoir owing to water management practices. Environmental variables, macroinvertebrates (zoobenthos and epiphytic fauna, zooplankton) and fish abundance and biomass were assessed at this biologically productive habitat to learn intraseasonal dynamics of food types, and their occurrence in the gut contents of small-sized roach, dace, perch, ruffe and three-spined stickleback. Gut fullness coefficient, niche breadth and niche overlap indicated how the fishes coexist in the macrophytes. Chironomidae dominated in the diet of the percids. However, ruffe consumed mostly benthic chironomids, while perch epiphytic chironomids and zooplankton. The diet of dace resembled that in fast flowing water although this rheophilic species occurred at unusual density there. The generalist roach displayed the lowest gut fullness coefficient values and widest niche breadth; consequently, intraspecific rather than interspecific competition decided the fate of roach. Three-spined stickleback differed from the other fishes by consuming epiphytic simuliids and fish eggs. The diet overlap between fishes reaching higher gut fullness coefficient values was rather low when the food associated with the submersed aquatic macrophytes was most abundant; this is congruent with the niche overlap hypothesis that maximal tolerable niche overlap can be higher in less intensely competitive conditions.

The food preferences of three-spined stickleback, Gasterosteus aculeatus L., downstream from a dam reservoir.

The food preferences of three-spined stickleback, Gasterosteus aculeatus L., downstream from a dam reservoir Submersed plants appeared in the impounded section of the Warta River as a consequence of low discharge in summer and were colonized by epiphytic fauna dominated by Hydra sp., Simuliidae, and Chironomidae. The three-spined stickleback consumed it voraciously, and their diet composition closely reflected the available food resources. In May their alimentary tracts were filled with Cladocera drifting from the reservoir, and then by the dominant taxa associated with macrophytes, especially chironomid periphyton scrapers. A comparison of dipteran head capsule width in the food resources and in the alimentary tract proved the three-spined stickleback preference for the largest larvae (optimal foraging strategy).

Percid occupation of submersed riverine macrophytes: food resource partitioning between perch (Perca fluviatilis L.) and ruffe (Gymnocephalus cernuus L.)

In a reservoir tailwater of the large, lowland Warta River, perch and ruffe coexist in a macrophyte habitat, which develops as a result of low water discharge in the late spring and summer. At the beginning of each year the diet of both percids, when shorter than 100 mm, is dominated by large, benthic Hydropsyche. Later in the year, epiphytic Chironomidae and Simuliidae replace these trichopterans in the perch diet, and benthic Chironomidae replace them in the ruffe diet. Large cladoceran species then become accessory food items for perch. Consequently, the food niche overlap of these two percids during the research period is only marginal.

Diet overlap between two cyprinids: eurytopic roach and rheophilic dace in tailwater submersed macrophyte patches

Abstract From May to August 2004, the available food base and diet of two cyprinid species, eurytopic roach, represented by 75 small specimens, and rheophilic dace, represented by 37 small specimens, were investigated in seasonal patches of submersed aquatic macrophytes (SAM) in the impounded lowland Warta River, Poland. The aim of the study was to recognize spatial and temporal patterns in the feeding of both species in relation to available resources, and to evaluate their food niche overlap. To distinguish homogenous classes of fish alimentary tracts on the basis of their contents, a Kohonen artificial neural network (i.e., a self-organizing map, SOM) was used. Indicator food categories were identified using the IndVal index. Roach and dace partitioned the food niche, which was demonstrated in this study by 1) insignificant values of the Schoeners interspecific diet overlap index on particular sampling occasions, and two SOM sub-clusters (homogenous diet classes) with alimentary tracts almost exclusively of roach (axis of resources), 2) zero or low percentage of specimens of both fish species coming from the same sampling occasions and assigned to any of the remaining homogenous diet classes (axis of time), and 3) absence of roach in May and dace in August in the SAM patches, i.e., on almost half of the sampling occasions (axis of space). The diet overlap was highest when the SAM patches and food base were most developed, which is congruent with the niche overlap hypothesis saying that maximal tolerable niche overlap can be higher in less intensely competitive situations. We recommend the combined application of SOM and IndVal index, which have both previously been used in biocoenology, to the analyses of animal diets. They effectively allowed getting insight into the complex trophic relationships.

Trace metal concentrations in free-ranger, tube-dweller chironomid larvae and a weakly polluted fluvial sediment

Abstract The objective of this study was to analyze macroinvertebrate assemblages dominated by Chironomidae (Diptera) and to assess the protective nature of these midges’ larval tubes against trace metals in the weakly polluted Bzura River. This low order lowland river flows through the Łódź City Municipal Area and is supplied by a large amount of organic matter from ecotones and a polluted roadside. Determination of metal content in sediments and chironomid tissue and tubes was conducted using atomic absorption spectroscopy. Our study has shown that the composition of chironomid assemblages was not determined by trace metals but rather by high organic enrichment, which caused the dominance of two species representing the same trophic group − gathering collectors − but differing in behavior. One of them belongs to free-rangers (Prodiamesa olivacea), while the other (Chironomus riparius) to tube-dweller larvae. Although the accumulation of certain trace metals in the tubes was found, the larvae of both types of behavior had a similar concentration of metals in their tissues, which proves effective metal detoxification in these insects.

Parental care compromises feeding in the pumpkinseed (Lepomis gibbosus)

Providing parental care is potentially costly. Costs can arise through elevated energy expenditure or from an increased risk of mortality. A cost of parental care can also occur because a parent is compromised in their ability to forage. We used pumpkinseed Lepomis gibbosus, a fish with an alternative male mating strategy, to test whether parental males differed in their feeding in comparison with females and cuckolder males. To address this question, we examined the stomach contents of female, cuckolder male, and parental male pumpkinseed during the breeding season over an entire diel cycle. We showed that parental males had a lower total weight of food in their stomachs in comparison with females, while cuckolder males did not. Parental males also had a lower weight and number of chironomids in their stomachs. The temporal pattern of feeding of parental males diverged from that of females, and they had a lower probability of pupal chironomids in their stomachs, which implies spatial segregation in foraging. Parental males had a greater probability of conspecific eggs in their stomachs than females, while the probability of egg cannibalism did not differ between cuckolder males and females. Overall, these finding meet predictions in accordance with an assumption that parental care and territoriality can compromise feeding.

Ephemera danica (Ephemeroptera: Ephemeridae) As a Resource for Two Commensals: Ciliated Protozoans (Sessilida) and Chironomids (Diptera)

Abstract The distribution and coexistence of two unrelated commensals, the chironomid Epoicocladius ephemerae (Kieffer 1924) and ciliate Carchesium polypinum L. 1758, on one host species, Ephemera danica Muller 1764, sampled in two small lowland rivers in 2009, 2010 and 2011, were investigated. We analyzed 288 mayfly specimens from the Bzura River and 101 from the Mroga River. The number of commensals on a single mayfly specimen varied between 0 and 18 chironomids, and from 0 to 46 colonies of ciliates. Prevalences were >48% for chironomids and ∼30% for ciliates, whereas mean intensities were low (4.01±6.04 commensals on one host). The spatial distribution of each commensal species was investigated on different parts of the host body. Neither chironomids nor ciliates infected the whole mayfly body. The co-occurrence of these two commensals was not random and showed a negative association. Chironomids were most frequent on two or three parts of the body (two parts of the abdomen, with gills and without gills, and legs), whereas ciliates were found on two parts (the whole abdomen). Coexistence of the two commensal species led to partitioning of resources that was host body size dependent: small mayflies (optimal size 11.63 mm) were primarily settled by ciliated protozoans while larger specimens (optimal size 28.77 mm) were settled by chironomids.