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Presented at the NABS Annual meeting, Vancouver, British Columbia, 2004
in Predation
Competitive interactions between the invasive gastropod Potamopyrgus antipodarum and baetid mayflies
C.A. Cada and B.L. Kerans. Department of Ecology, Montana State University, Bozeman, Montana USA
The nonindigenous gastropod Potamopyrgus antipodarum is quickly spreading through aquatic environments in the western United States, and populations often occur at very high densities. In the Madison River drainage (Montana, USA), densities of Baetidae decrease when sympatric with P. antipodarum, suggesting exploitation or interference competition. To determine when P. antipodarum has the greatest effect, we quantified densities of P. antipodarum and three baetid mayfly species in low-snail and high-snail density reaches on a monthly basis for 18 months. Decreased densities in high-snail reaches suggest that Baetis tricaudatis was most affected by competitive interactions in winter, while densities of Diphetor hageni decreased in autumn. An increase in densities of Acerpenna pygmaeus in autumn suggested facilitative interactions with P. antipodarum or competitive release from another competitor. Using an in situ experiment with a response-surface design, we quantified the magnitude of intra- and interspecific competition between B. tricaudatis and P. antipodarum using mortality and per-capita growth as response variables. Mortality in low-density treatments did not differ, but mortality at high-densities was greatest in combination treatments indicating interspecific competitive effects for both species. This experiment confirms that decreased densities of B. tricaudatis in the field result from competitive interactions with P. antipodarum.
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