Habitat characteristics contributing to local occupancy and habitat use in rock pool <Emphasis Type="Italic">Daphnia</Emphasis> metapopulations |
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Authors: | V Ilmari Pajunen Irmeli Pajunen |
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Institution: | (1) Department of Biology, Stephen F. Austin State University, SFA Station, P.O. Box 13003, Nacogdoches, TX 75962-3003, USA |
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Abstract: | The effects of invasive macrophytes, water level fluctuations and predation on freshwater unionids Pyganodon grandis and Utterbackia imbecillis were studied in three small impoundments in Northeastern Texas in 2003–2005. Mussel density was sampled with quadrats. Mortality,
associated with the water level fluctuations and predation, was estimated by collecting dead shells on the shore at about
two month intervals. In two ponds, horizontal distribution of unionids was limited by dense beds of invasive and noxious macrophytes
(mainly Eurasian watermilfoil Myriophyllum spicatum and American lotus Nelumbo lutea): mussel densities were significantly lower in these macrophyte beds (P < 0.001). In the third pond with the lowest density of macrophytes (stonewort Chara sp.), unionids were distributed more evenly, and the average unionid biomass was the highest among all ponds studied. Vertical
distribution of unionids in all ponds was likely limited by low oxygen at depth >2 m. The total amount of shells found on
the shore per year varied from 0.1% to 28% of the total population in the pond and was negatively correlated with water level
(r = −0.72 to −0.81, P < 0.005). Mammalian predators consumed up to 19% of the total unionid population and predation was facilitated by water level
fluctuations.
Handling editor: K. Martens |
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Keywords: | Pyganodon grandis Utterbackia imbecillis Unionidae Density Distribution Water level fluctuations Myriophyllum spicatum |
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