ADAPTATIONS OF SURVIVAL VALUE 



A few new observalions on the [^rairie spadetoot, S. bonibijrons Cope, 

 should also be noted. In most pools utilized by tadpoles of this species, water 

 is deep enough to allow development of algae and other food sources. In shal- 

 low water, however, these tadpoles may also utilize bottom mud. I have 

 checked the intestinal contents of several tadpoles Irom such p(K)ls antl luul 

 the same conditions as in 5. hurteru. 



Social feeding aggregations of tadpoles of this species have not been 

 recorded previously except cannibalistic aggregations at one site where food 

 was scarce (Bragg, 1946, 1948). On June 4, 1948, my assistant in the Uni- 

 versity of Oklahoma Biological Survey, Mr. Harold Dundee, and I found 

 a long, shallow ditch of clear water in northern Creek County, Oklahoma, 

 swarming with large tadpoles of >S. bombijrons. At the southern end where 

 the water was very shallow, several large feeding aggregations were present, 

 the animals in them feeding voraciously on the bottom materials in exactly 

 the manner noted many times in 5. hurterii. These were not cannibalistic 

 aggregations. The ditch was approximately 150 feet long by 5 feet in width 

 (maximum), and the maximum depth of water at the time was 6/2 inches. 

 The temperature of the water was 33° C, both in the region of the aggrega- 

 tions and near the center of the pool where there were no aggregations. A 

 small number of grass blades protruded from the surface but there were no 

 algal mats present. I would classify the pool as of Type 1 (i.e., similar to pools 

 A, B, D, and F of the S. hurterii studies). 



Later in the season (early July) we found several stations in western 

 Oklahoma where tadpoles of S. bombijrons occurred in water from Vi inch 

 to 2 inches in depth. These pools, however, were the remains of formerly 

 extensively flooded, planted land. In all of these places the water was turbid, 

 thus little detail could be seen as to behavior of the tadpoles; but there was 

 no evidence of aggregations. In this shallow water, behavior of that kind, 

 had it occurred, could scarcely have been missed, especially since I was acutely 

 aware of its possibility. These tadpoles had also ingested large quantities of 

 bottom mud which, indeed, seemed the only source of food. In former years, 

 I have seen these same phenomena many times. It seems, therefore, that mere 

 shallowness of water does not necessarily result in feeding aggregations in 

 the prairie spadefoot, even when desiccation is imminent and bottom mud 

 the main or sole source of food. 



There is still another aspect of this problem which needs consideration. 

 It has been noted many times that where few tadpoles of S. hurterii occur 

 (either in nature or in laboratory cultures) social aggregations never develop. 

 It seems, therefore, that the number of individuals present has some influence 

 on behavior. It has also been noted that spadefoot tadpoles are often crowded 

 in natural waters but no data have been presented which would indicate this 

 quantitatively. Since several of the pools studied most intensively are fairly 

 regular in shape and of reasonably uniform depth it is possible to figure, with 

 a small degree of error, the volume of water available to each tadpole, pro- 

 vided, of course, the approximate number of tadpoles at any one time and 

 place is also known. 



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