Selectivity and competitive interactions between two benthic invertebrate grazers (Asellus aquaticus and Potamopyrgus antipodarum): an experimental study using 13C‐ and …
Freshwater Biology, 2005•Wiley Online Library
Tracer experiments with two diatoms labelled with 13C (Nitzschia palea) and 15N (Fragilaria
crotonensis), were conducted to investigate feeding selectivity and interspecific competition
between the grazers Asellus aquaticus (Isopoda, Crustacea) and Potamopyrgus
antipodarum (Hydrobiidae, Gastropoda). Conventional methods, such as cell counts and
estimated biovolume, were used first to detect feeding preferences within the different grazer
treatments. 2. The results revealed a significant decline in algal biovolume in all grazer …
crotonensis), were conducted to investigate feeding selectivity and interspecific competition
between the grazers Asellus aquaticus (Isopoda, Crustacea) and Potamopyrgus
antipodarum (Hydrobiidae, Gastropoda). Conventional methods, such as cell counts and
estimated biovolume, were used first to detect feeding preferences within the different grazer
treatments. 2. The results revealed a significant decline in algal biovolume in all grazer …
Summary
1. Tracer experiments with two diatoms labelled with 13C (Nitzschia palea) and 15N (Fragilaria crotonensis), were conducted to investigate feeding selectivity and interspecific competition between the grazers Asellus aquaticus (Isopoda, Crustacea) and Potamopyrgus antipodarum (Hydrobiidae, Gastropoda). Conventional methods, such as cell counts and estimated biovolume, were used first to detect feeding preferences within the different grazer treatments.
2. The results revealed a significant decline in algal biovolume in all grazer treatments and no indications of active selectivity were observed. In contrast to conventional methods, measurements based on isotope signatures showed strong differences in tracer uptake, thus indicating different degrees of assimilation and digestion by the two grazers.
3. The selectivity index Q, which provides information on the uptake ratio of 13C to 15N, showed a significant time effect for both grazer species and a significant difference between single‐ and mixed‐grazer treatments for P. antipodarum. Thus, this technique enabled the direct quantification of the uptake by grazers and, therefore, served as an ideal tool for the detection of passive selectivity.
4. Our results indicate a shift in feeding preferences related to between‐species competition and a potential divergence of trophic niches when species coexist.
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