40 ECOLOGY AND LIFE HISTORY OF THE COMMON FROG 



of gravel. This was the normal place in all the years of observation of 

 this pond. By 19th April, it became clear that, unless rain fell soon, the 

 w^ater in this bay would evaporate, the tadpoles would perish, and with 

 them would disappear the opportunities of observation. I therefore 

 transferred some of them to the main pond, leaving some in the pool at 

 the spawn site. The graph shows that, although the tadpoles at the 

 spawn site were apparently living in such unfavourable conditions, 

 and the transferred tadpoles had all the pond to swim in, the two sets 

 fared about equally. In fact, on 15th May, when the water at the 

 spawn site was confined to a few hollows made by the hooves of a 

 cow, the tadpoles in these holes had an average weight a Httle higher 

 than those of the transferred tadpoles, hving so far apart from one 

 another that persistent efforts with the net were necessary to collect 

 any. The rate of growth of the pond tadpoles was never high. It was, 

 it is true, higher than in the very crowded conditions in Lower Park- 

 field at the same time, but lower than at Dagger Lane where tadpoles 

 were much more numerous. 



It will by now be clear that any attempt at a concise generahzation 

 summarizing the life of a tadpole would merely be inaccurate. It is, 

 however, possible to point to some salient and recurring features. 



Evidently, tadpoles living at liberty in the pond in which the parent 

 frogs laid their eggs do not always have enough to eat. The catastrophe 

 at Lower Parkfield admits of no other explanation, but, even in the 

 other ponds, the maximum growth rate that the species is capable of 

 reaching, for example at Cat Hill, is not often found. Moreover, the 

 colonies of small tadpoles in a pond that also has colonies of larger 

 tadpoles, quite a general phenomenon, must surely mean that there are 

 some places that provide a better hving than others. It must be 

 remembered that usually all the tadpoles come originally from the 

 same place, and hatch within a few days of each other. How does it 

 happen that these colonies arise? What maintains the size differences, 

 and how do these originate? 



There is no difficulty about the origin of the size differences. In 

 Chapter i it was shown that the tadpoles used for the chemical analyses 

 differed considerably from batch to batch. All tadpoles are not born 

 equal. Moreover, in the tadpole world, it is the thruster that gets 

 ahead, as the following observations show. 



I have no observations on R. temporaria to draw upon, and my 

 example is taken from the toad, B. bufo. There is therefore an element 



