How does predation from fish influence the benthic invertebrates’ species composition in the Phragmites australis and Chara vegetation of Lake Takern?
Predation is one of the important selective factors that regulate the species composition of benthic invertebrate communities. The study objective was to investigate the invertebrate distribution in two contrasting habitats in Lake Takern, southern Sweden, submerged Chara vegetation and emergent Phragmites australis vegetation, and to investigate the influence of predation from fish on certain invertebrates. Laboratory studies were used to estimate handling time and the intake rate (mg/sec) by the fish based on the optimal foraging model. In the field, fish and invertebrates were collected with gill nets and hand nets respectively and the fish gut content was analyzed. In total, sixteen invertebrates’ taxa were collected from the two habitats. The proportion of the invertebrate’s overlaps from each of the habitat was calculated by Renkonen index and with Sorensen diversity index. Both indices showed a similarity larger than 65%, indicating that there was no significant difference in the invertebrates’ distribution in the P. australis and the Chara habitat. The fish caught with the gill nets were: roach (Rutilus rutilus), perch (Perca fluviatilis), tench (Tinca tinca), and rudd (Scardinius erythrophthalmus). The caught perch had eaten: Asellus aquaticus, Gammarus lacustris, Corixidae, and the larvae of Chironomidae and Zygoptera.A comparison was made on the invertebrates found in the field and the ones observed from the gut of the perch, and the findings were that the invertebrates that had more occurrence in the gut were less in proportion in the benthic samples. In the laboratory experiment perch ( Perca fluviatilis) was used as the predator fish and the prey organisms were Asellus aquaticus,Gammarus pulex, and Corixidae of three size categories. The results showed that perch handling time for A.aquaticus of the different size categories, was not significantly different (p>0.05); and the same results were valid for Corixidae and G. pulex. However, the intake rate of perch across the prey and their size categories were significantly different. The handling time was not significantly different which means that the predator fish will gain more in terms of intake rate as it prey on larger size prey items, thus harmonizing with the optimum foraging theory.
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