Competition and facilitation within and between a snail and a mayfly larva and the effect on the grazing process |
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Authors: | Pia Hertonsson Kajsa Åbjörnsson Christer Brönmark |
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Institution: | (1) Department of Ecology/Limnology, Lund University, Ecology Building, Lund, 223 61, Sweden |
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Abstract: | We studied the competitive effects within and between two taxonomically distant freshwater herbivores, a snail and a mayfly,
common in Swedish lakes, Lymnaea peregra and Cloeon dipterum, respectively, and their effect on grazing in a laboratory experiment. The experimental set-up consisted of 2-l aquaria,
each containing a periphyton covered tile. Intra- and interspecific effects were tested by increasing the density of one species
at a time in four different treatments, (1) snails (intraspecific treatment), (2) mayflies (intraspecific treatment), (3)
mixed-snails (interspecific treatments, snails kept constant) and (4) mixed-mayflies (interspecific treatments, mayflies kept
constant). Intraspecific competition affected both snails and mayflies negatively, i.e. increasing mortality with increasing
con-specific density. Furthermore, there was a decrease in snail growth with increasing snail density. In the mixed-species
treatments both species changed their microhabitat use indicating interspecific competition. Despite this, we also found a
positive effect of mayfly density on snail growth, most likely due to indirect commensalism. No density-dependent effect of
grazing on periphyton was found, probably due to interference competition between grazers. However, there was a significant
difference in periphyton biomass, due to species composition of grazers. Irrespective of their densities, if they co-existed,
the two grazer species decreased the periphyton biomass significantly compared with both single-species treatments. We considered
this as a joint action of facilitation and interaction. Our results suggest that competition can be an important structuring
factor in macroinvertebrate communities and that species composition can be significant for ecosystem processes within lentic
environments. |
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Keywords: | Ephemeropteran Grazing Intraspecific Interspecific Mollusca Periphyton |
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