VI 



Observations on the Ecology and Natural History of Anura. 



XVII. Adaptations and Distribution in Accordance 



with Habits in Oklahoma^ 



ARTHUR N. BRAGG 



IT HAS often been said that the goal of evolution is adaptation to a chang- 

 ing environment; from this it follows that any organism expresses in 

 structure and in behavior the accumulation of adjustments throughout 

 its phylogeny; and this is as true of a species, genus, or other taxonomic group 

 as of an individual. Organisms must vary in order to remain in adaptation 

 to the environment if they are to continue existence in any given place. 



Most studies of phylogeny, taxonomy, and distribution of organisms tend 

 to emphasize the morphological changes which occur as organisms come 

 under varying environments. By comparing large series of specimens and 

 emphasizing their differences in relation to distribution, the direction of dis- 

 persal, as well as anatomical trends in adaptation, are discovered and then 

 expressed in a scheme of classification. These studies are of great value but 

 even the best of them are apt to be weak in that (1) they tend to emphasize 

 geographical as opposed to ecological distribution, and (2) they tend to over- 

 look behavior and habits. 



That habits especially have been neglected is easily shown by references 

 to the Salientia. As pointed out elsewhere (Bragg, 1940d) many species (e.g., 

 Bufo compactilis Wiegman and Bujo cognatus Say) had been known taxo- 

 nomically for over a century and their geographic distribution fairly well 

 worked out before anyone paid much attention to their ecological require- 

 ments or to their patterns of breeding behavior. Pseudacris darJ^ii (Baird) and 

 Ps. triseriata Wied are still uncertain taxonomically but differ in ecological 

 requirements and in habits (Bragg, 1943, 1943a). The leopard frogs of 

 North America are very difficult to separate structurally and their specific 

 or subspecific relationships have not been worked out satisfactorily (Burt, 

 1931; Kauffeld, 1937; Stejneger and Barbour, 1939; Wright and Wright, 

 1942; etc.) but the eastern forms differ from those of Oklahoma in habits in 

 such a way as to indicate that there is a very distinct difference among them 

 (Bragg, 1940, 1941). 



1 Contribution from the Zoological Laboratory of the University of Oklahoma, aided 

 by a grant from the Faculty Research Fund of the University and finished under a Grant 

 in Aid of Research from the American Association for the Advancement of Science. Ac- 

 knowledgement also is hereby made to Dr. A. Richards, Director of the University of Okla- 

 homa Biological Survey, who has read the manuscript critically and to Dr. A. O. Weese 

 and Dr. Charles C. Smith for various aids and suggestions as well as for aid with the figures. 



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