Juday, Chancey (ed.) / Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume XXI (1924)
Baker, Frank Collins
The fauna of the Lake Winnebago region, pp. -146 PDF (11.3 MB)
Baker-The Fauna of The Lake Winnebago Region. 131 Table 5 shows the relation of the number of species of Mollusca to the depth of the water. The greatest variety is found at depths not exceeding two meters. Table 6 shows the relation of the number of species of Mollusca to the character of the bottom in Lake Winnebago. The maximum number was found on sand bottom. Table 7 shows the variety of the molluscan faunas of three lakes, namely, Oneida Lake, New York; Maxinkuckee Lake, Indiana; and Lake Winnebago, Wisconsin. One of the interesting features brought out by the study of the molluscan fauna of the Lake Winnebago region is the difference in size and shape between the Unionidae of the Fox River and those of the lakes, a difference which appears to be comparable to that noted by Grier (1919) between the Naiads of Lake Erie and the upper drainage of the Ohio River. Grier states that "if we put a shell in the lake environment we may expect it will change its morphological features, not at random, but in a distinct, deter- minate, or orthogenetic direction. " This change in the morphology of shells that have migrated from a river to a lake is strikingly shown in the Lake Winnebago fauna, and a study of the two areas by the methods of Grier would produce the same results as attained by the study of the Lake Erie shells. It is a significant fact that the same varietal forms inhabit both Lake Winnebago and Lake Erie, indicating that the law holds good under similar conditions in widely separated areas. Dr. Sterki notes that almost all of the Pisidium of the lake are small and slight, some even depauperate, and Sphaerium and Musculium are similarly affected. The gastro- pods of the lake are in the main different from those of the river. Thus the entire molluscan fauna is affected by the same law of variation produced by river and lake environment, clearly indi- cating that ecological station plays a large part in the evolution of species. A study of the tables and of the systematic list which fol- lows will bring out additional features of this ecological character- istic. Just what factors have been potent in producing these changes does not seem to be definitely known. It is probable that variation in food supply, in the chemical character of the fluid medium in which they live, as well as in the general physical environment, plays a large part in these changes of form.
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