THE AMPHIBIA OF OKLAHOMA 



species in Oklahoma have been seen hundreds of times whereas a few known 

 to be present have not been seen at all during breeding. A few have been dis- 

 covered only rarely but the majority of the twenty-seven forms known in 

 Oklahoma have been studied in at least ten diflferent pools, some in as many 

 as fifty or more. 



Recently it has become possible on approach to a given pool to predict 

 the species of tadpoles to be found in it (or recently metamorphosed juveniles 

 about it) with a fair degree of accuracy. At first the basis of prediction was 

 vague and subjective, being derived from unconscious correlations made 

 through experience. But since predictions must have an objective basis (even 

 though a complex one), an attempt has been made to analyze the major 

 factors in it. The results of this analysis are given below and some of the 

 factors for several species illustrated in the figures. 



In correlating field observations of this sort, care must be taken to avoid 

 the many possible sources of error. For example, the tadpoles or juveniles 

 may not be present at a given time and place for one of the following reasons: 

 (1) The pool may have been formed under weather conditions inhibiting 

 breeding of some species. This will often be true in prairie, for example, 

 among those species (e.g., Bufo cognatus, B. compactilis, B. msidior, Micro- 

 hyla c. olivacea) that have the xeric pattern of breeding. (2) A species may 

 be rarely represented in the neighborhood of the pool and, through chance, 

 all males may have happened upon other pools in the region rather than the 

 one examined. (3) Males may have called here in small numbers only and all 

 females may have been attracted by the louder clamoring of more males 

 about adjacent pools and hence laid eggs in them (more especially true of 

 species limited to prairie). (4) Breeding may have occurred but all tadpoles 

 may have succumbed to predators in this pool. This condition must be rare 

 but can occur wherever predators occur in large numbers. One case is on rec- 

 ord where all of the thousands of tadpoles of Bujo cognatus in a bufTalo 

 wallow disappeared progressively as tadpoles of a known predator (Scaphi- 

 opus bombijrons) increased in dominance and individual sizes (Bragg, 

 1940). (5) There may originally have been many tadpoles, all of which were 

 killed by evaporation of the water; subsequently, the pool may have formed 

 again without further reproductive activity. (6) In several species (e.g., Acris 

 crepitans, Microhyla c. oliuacca, Rana berlandieri , Bufo tv. woodhousii) not 

 all females produce eggs at the first favorable condition within a given season. 

 Should all females near a given pool fail to reproduce, no tadpoles of these 

 species will be found here, even if breeding is known to have occurred else- 

 where. 



Of course, there may be other factors which should be considered; but 

 enough has been noted to show that unsuitability of a pool for the breeding 

 of any given species is not indicated merely by the absence of tadpoles, even 

 when one knows that the species could have bred prior to a given date in the 

 region indicated. Negative evidence does have some value, however, when 

 consistently negative results can be correlated with one or more character- 

 istics of a pool, such as depth, extent, vegetation, permanence, or contamina- 



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