Geological Features and 

 Algal Distribution 



Some species of aquatic plants may have a wider geographical dis- 

 tribution than terrestrial forms. This is true, for the most part, 

 because of the more nearly universal similarity of aquatic habitats 

 and the somewhat greater constancy of the factors which play a role 

 in determining distribution. It need only be mentioned, by way of 

 illustration, that in an aquatic habitat nutrients are more equally 

 diffused and more readily obtained, temperature changes more 

 gradual, and annual temperature range less, than in a terrestrial 

 environment. 



Ecologists, however, not infrequently assume a more universal 

 distribution for aquatics than may actually exist; in a recent excel- 

 lent volume on ecology one finds a complete disregard of plants in 

 an aquatic environment. Facts bear out the reasonable assumption 

 that habitats with similar floras have the necessary determining 

 physical-chemical conditions in common. Where there are variations 

 in the flora and when there is an absence of widely distributed 

 species from certain habitats, correlated modifications in the environ- 

 mental factors, sometimes obscure, must be sought for. As is well 

 known, species are subject in their distribution, in water as on land, 

 to limitations imposed by the presence or absence of certain ecologi- 

 cal factors. Less than minimal requirements of salts, carbon dioxide, 

 nitrogen, phosphorus or other nutrients, the degree of illumination, 

 and temperature changes are a few of the factors involved in distri- 

 bution and habitat selection. 



The part ecological factors play in determining quantity and qual- 

 ity of algal floras is readily appreciated in a study of lakes in this 

 area, famous for its great number of inland bodies of water, bogs, 

 and forested swamps. In Michigan there are about 11,000 lakes, 

 with a total area of 1137.6 sq. mi.; Antrim County has 10.1 per cent 

 of its area in lakes, and several other counties have nearly as much 

 (Brown, 1943). In Vilas County, Wisconsin, the area occupied by 

 lakes is 15 per cent of the total, although this figure does not include 

 the innumerable small ponds, permanent pools, and spring-like 

 seeps where algae abound. It is estimated (Juday, 1914, p. xi) that 



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