GENERAL LIFE HISTORY OF THE TADPOLES 



39 



rather exceptional event, although they were quite close together. 

 Moorhens did not attack the spawn, but few tadpoles survived and, on 

 1st May, none could be found in the open pond. Some were, however, 

 found in a small pool alongside a drain leading under the road. After 

 three weeks, drought began to isolate this pool from the pond and, on 

 14th May, it only measured about 20 x 24 cm and, on 21st May, the 



MG. 

 400 



300 



200 



100 



•P<DOL 



<|>-sPAWfli siIte 



<§>-^ 



10 20 30 

 APRIL 



10 20 SO 

 MAY 



O 20 SO 



MAY 



Fig. 14. Bentley Heath Village Pond, 1949 {left) 



A study of a doomed population in a pool that was drying up. Growth 

 was good at first, and the decline set in under very crowded conditions. 



Fig. 15. Green Street Pond, 1947 (right) 



Another study of a doomed population. The tadpoles in the marsh were 

 in very small volumes of water, but not very crowded, and fared well until 



the end. 



water was on the point of complete evaporation. The graph shows the 

 changes in weight of a tadpole population at the limit of possible living 

 conditions, brought about by entirely natural causes in a natural 

 environment. It shows that until the conditions had become obviously 

 desperate the tadpoles grew well. 



Green Street Pond 



1947 (Fig. 15). Here the frogs laid about fifty clumps of spawn in a 

 bay opening out of the marsh bordering the main pond, behind a bank 



