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Thirty-four species of molluscs have been found in the drainage systems of the United States Military Academy at West Point, NY. A few rare species were found as well as a single specimen of a presumed new gastropod taxon. Only two species of unionids, Pyganodon cataracta and Elliptio complanata, were found within the drainages. The largest drainage system, Popolopen Brook, contained the highest diversity of molluscs. Species redundancy between drainages aligned well as a function of the extent of lentic and lotic habitats with brooks and streams having a Bray-Curtis similarity index of ≈ 64.0 when compared to lakes and ponds. On the other hand, a number of species collected were found in only a single drainage. Total drainage area did not correspond well with diversity unless determined as total predicted usable habitat. Thus the drainages with the greatest number of discernible lakes, ponds, streams, and creeks, also had the highest molluscan diversity. On the whole, molluscan diversity of these drainages compared favorably to those of other regional New York sites, but relative abundance or population densities varied, with variations reflecting survey effort, time or season of collections, and incorporation of historic museum collections.
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Barbour's Pond is a 4.45-ha pond located in Garrett Mountain Reservation in Passaic County in northern New Jersey, one of the most densely populated regions in the United States. Despite its small size and surrounding urban sprawl, the shallow waters of this pond hold 18 species of molluscs. Monthly samples from March 2004 through March 2006 found the highest diversity in December 2004, and in January, June, and July 2005. Additional samples were taken in April 2007 and May 2010 to spot-check relative diversity years after the original sampling period. Total molluscan abundance was greatest in July and November 2004, possibly reflecting new late spring and autumn cohorts. Univariate statistics demonstrate that this pond has a temporally stable and diverse malacofauna. Analysis, of basic environmental parameters including temperature and pH, however, showed little correlation with molluscan diversity over time, underscoring the stable yet complex nature of biodiversity of this small urban pond.
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Freshwater unionid mussels produce a bilayered shell with the mineral proportion comprising an outer prismatic and an inner nacreous layer. The shell is the animals’ primary structural means of protection from predators and environmental challenges; therefore, variations in shell strength and properties may lead to differences in survival. Few studies have systematically assessed shell properties in unionids. A major challenge in such work is separating effects of environment from those of evolutionary history, because ultimately, both can affect shell properties. We collected eight species of unionids within a small area of the Allegheny River, Pennsylvania, that was relatively homogeneous in substratum type and other environmental characteristics. For each species, we quantified shell thickness, including thickness of the prismatic and nacreous layers, and shell micromechanical properties (microhardness and crack propagation, a measure of fracture resistance) in three regions of the shell. Shell thickness varied dramatically among species and was about five times greater in the thickest-shelled species, Pleurobema sintoxia, than in the thinnest-shelled species, Villosa iris. Because all species experienced similar environmental conditions, variation in shell thickness can be attributed largely to evolutionary history. In contrast, microhardness and crack propagation showed little variation among species. Given that micromechanical properties are similar among species, shell strength may be largely a function of thickness. These results have conservation implications, as differences in shell thickness could reflect relative vulnerability to predators and physical conditions
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