THE AMPHIBIA OF OKLAHOMA 



The number of eggs in a single clutch of S. hurterii had not been de- 

 termined. Through the years, I have seen egg masses of single females that, 

 because I wished later to study the tadpoles in the pools, were not disturbed. 

 All of these have appeared to be comparable in size and to contain comparable 

 numbers of eggs. It seemed safe, therefore, to assume that any one clutch 

 would be representative of the species so far as approximate numbers of eggs 

 is concerned. Therefore a single clutch of eggs laid by the female of a pair 

 found in amplexus in Pool F was collected, every care being taken to get all 

 of the eggs. They were preserved in formalin as collected and later counted 

 twice, in groups of fifty to minimize the chance for error. The number of 

 eggs was 3,586. Some variation is to be expected but it seems reasonable to 

 assume that, in round numbers, 3,600 eggs is representative of a clutch in 

 S. hurterii. 



In Pool F a single clutch has been produced on several occasions; nearly 

 all these young have hatched. This pool measures close to 41 X ^-5 X Vi, feet, 

 a volume of 119.6 cubic feet maximum, assuming dimensions the same 

 throughout. Since the depression in which the pool forms is actually some- 

 what shallower and narrower at the two ends, 100 cubic feet will probably 

 be nearer its maximum volume. If we assume 3,500 of the potential 3,600 

 eggs of a single clutch to hatch, this gives thirty-five tadpoles per cubic foot 

 of water. Within a week the water level usually falls to five inches or less 

 and the tadpoles are at least twice their size at hatching. Even though these 

 figures give only the approximate condition, it is easy to see that the animals 

 may become very crowded. Similar calculations at Pool C, which is more 

 uniform, and hence the figures more accurate, indicate conditions somewhat 

 similar. The pool will contain not over 700 cubic feet of water which gives 

 five tadpoles per cubic foot initially. However, the water level here drops 

 rapidly and in a week's time the depth is not over two inches, usually one 

 and one-half. If we assume a mean depth of 1.75 inches, then the amount of 

 water is 306-|- cubic feet, each containing approximately eleven tadpoles. 

 This is on the assumption that only one clutch of eggs is produced. Since 

 two and sometimes three clutches of eggs are often laid here on the same 

 night, it takes no great imagination to see that these animals are usually very 

 crowded, especially as they increase in size. Their numbers are actually de- 

 pleted somewhat by predators, especially larval beetles ( Hydrophylidae and 

 Dytiscidae principally) but not nearly enough to affect the principle that 

 each tadpole has progressively less room as the water level falls. It should be 

 noted also that crowding is also enhanced by the presence of many tadpoles 

 of other species. 



Discussion 



The whole pattern of tadpole development in these spadefoot toads sug- 

 gests an adaptation to development in shallow, temporary pools in a xeric 

 environment. Even the breeding habits of the adults, at least of S. hurterii, 

 fit this hypothesis and on the average work toward the survival and meta- 

 morphosis of maxinuiiii numbers of young. 



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