THE AMPHIBIA OF OKLAHOMA 



balance replenishment by seepage from above, so that a nearly constant water 

 level may be maintained for as long as two months. Algae of many species 

 are abundant and a growth of smartweed (Polygonum fiuitans (Eaton) 

 Green, (as kindly identified by Dr. Aven Nelson) springs from the bottom 

 early in the season, shading the pool and often nearly covering the water 

 before total evaporation occurs. 



It should be recalled that pools C and D lie immediately adjacent to each 

 other and receive their water from essentially the same source (Bragg, 1945) 

 and that pools E and F are only a few hundred feet away, occupying higher 

 portions of the same slope. Pool A lies ten miles, and Pool B, two miles, to 

 the west of the others. All these pools are in the oak-hickory savannah as de- 

 fined by Bragg and Smith (1943) and all are exposed to direct sunlight ex- 

 cept Pool B which was not studied in 1948. 



Pools of type 1 obviously tend, on the average, to develop less organic 

 matter than those of types 2 and 3. During the dry phase of the evaporation 

 cycle, the bottoms of pools B, D, and F are commonly bare, sun-cracked clay 

 (scattered sedges in D and sometimes in F excepted). A thin film of darker 

 organic residue commonly covers the bottom. The soil in the region is loose, 

 sandy clay loam (known locally to be poor farming land) which gives little 

 evidence of influencing the pools, from the viewpoint of tadpole development. 



Not uncommonly water evaporates so rapidly from these pools (except 

 Pool E) that all of the tadpoles are caught in pockets of water, flounder there 

 for a few hours in soft mud, and die. This may happen two or three times 

 during a season or not at all in any one place, depending upon local condi- 

 tions of temperature, wind, and rainfall. It is very common in late spring and 

 summer to find dead tadpoles dried up on the bottoms of former pools, and 

 of course, this includes tadpoles of all species present, not just those of spade- 

 foots. Despite the activity of scavengers (birds, ants, etc.) which eat some 

 of these, dead tadpoles add materially to the organic matter in the bottom 

 of the pools when these are again filled. 



In pools of type 1, dried tadpoles appear to be the major source of organic 

 materials. In pools of type 2, they supplement plant remains. In pools of 

 type 3, they are of minor significance since they so rarely are killed by total 

 evaporation. 



Where water is very shallow, as in pools C and F, the evaporation cycle 

 passes quickly and more tadpoles are killed than in other types, thus rapidly 

 building up organic matter at these pool sites. Where water is deeper, as in 

 pools A, B, and D, in contrast, these cycles pass less quickly and more tad- 

 poles undergo metamorphosis. Their transformation has the efFect of taking 

 organic matter from the pool rather than adding to it, and thus of depleting 

 the limited supply. Eventually, there comes a time in these pools when or- 

 ganic matter is insufficient in amount (or kind) to supply the nutritional 

 needs of thousands of tadpoles and it may take several evaporation cycles 

 (months or years depending upon local conditions) to furnish again the 

 necessary food sources of the proper kinds for tadpoles to develop successfully. 



This explains several facts earlier quite puzzling. Pool A supported tad- 



104 



