Report of the Committee on Paleoecology, 1935-1936: Presented at the Annual Meeting of the Division of Geology and Geography, National Research Council, May 2, 1936 (1936) / Chapter Skim
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Organisms and their Environment - W. H. Twenhofel
Organisms and their Environment - W. H. Twenhofel
Pages 1-9
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Every organism lives where it does because the combined impact of all the environmental conditions permits it to live there. 'JIhe relations thus existing between an organism and its environment constitute that division of biological scionco tormod oculogy.
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Soma organisms and some animal communities seem to be essentially independent of the physical factors of the environment and yet these were not found to have general distribution. The answer was found in the biological factor whereby certain animal communities can not exist in the face of competition of other animal communities and in the illustration given by Petersen it is stated that the Macoma animal community is essentially independent of many physical conditions, but, nevertheless, it does not have general distribution over the bottom.
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Thus, the modification of an animal community may ultimately be caused by some non-apparont factor that vitally affected an insignificant member of an adjacent plant community. Eliminate the gooseberry and currant from a region, the \vhite pine blister is at the same time eliminated, and the white pine thrives and it may thus set up a white pine forest with submergence of other forest trees and develop a fauna dependent upon the white pine and its associates..
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18 meters, coarse gravel with sand, clay and pebbles, 10.S°C. The geographical distribution of the various animal communities on the nearly level bottom is: Macoma, on all southern coasts of Denmark and in Baltic.
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He states "All attempts in the past to delineate Lpwer Devonian provinces have failed to take into consideration the fundamental factor of the physical environment, and its resultant impress upon tho sediments, and upon the contained faunas." He suggests "that facies has been the dominant element in the distribution of the marine faunas of this period. Ihe evidence points to a cosmopolitan fauna, which, as today, would vary with such factors as temperature, light, salinity, food conditions and so on".and tint it is "possible to state that the Heefton fauna is most closely related to that of the same age In V/estern Europe not because of geographical .station, (1)
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"The chief condition governing the distribution of these Lower Emsian faunas appears to have been the degree of clearness of the water. It is, however, impossible to assess the value of such factors as salinity, temperature, and competition." "Where the physical conditions are identical, even in widely separated areas, the characteristic fossils of the same age are identical or closely related." "Certain Lov;er Devonian types appear to have had a wide range of physical stability, and occur in strata of various facies." "These types ....are of groat importance in that they allow correlation from facies to facies." Some of the problems of the New York Devonian stratigraphy have been "'I Twenhofel, W
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into each others door-yards, .and all holding the same definite time value."• Cooper (2) has shown that the Devonian Hamilton of western New York changes lithology when traced eastward from blade shales in the west to ultimately pass into red beds, largely sandstones, formerly assigned to the Catsid.ll.
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lias statod that in the Paleozoic strata "as far as present observations pormit it appears that wherever cephalopods are abundant the mobile gastropods also are relatively comnon, while the sedentary brachiopods, corals, and bryozoans are less common than elsewhere. On the contrary, where the bracliiopods, corals, and bryozoans are common, cephalopods usually are rare." "Possibly segregation is due occasionally to violent storms resulting in strong ocean currents which sweep along the mobile forms into areas whore sedentary life is less abundant, overwhelming these mobile forms with muddy and arenaceous deposits.
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de Laubenfels of Pasadena Junior College of Pasadena, California; and the paleoecology of the Paleozoic plants by C
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