28 ECOLOGY AND LIFE HISTORY OF THE COMMON FROG 



dense stand, an event never known before in the many years of obser- 

 vation of this pond. 



Spawning was much earUer than in 1947. The number of clumps 

 was not much different, perhaps shghtly fewer, and they were laid in 

 the shallows about 1-2 m away from the place where the floating 

 weed had been in the previous year. Hatching was in progress on 3rd 

 April, and there was an aggregation on the envelopes until 19th April. 

 During the whole of the rest of the season, no dense aggregation was 

 seen anywhere in the pond. It was estimated that the tadpole popu- 

 lation was only about i per cent of that in 1947. Reference to Fig. 6 

 shows that the growth rate was at first very slow. On ist May, there 

 were still no obvious patches of algae, and the tadpoles were feeding 

 on the bottom of the pond. On 8 th May, however, a patch of algae 

 was seen at "Sallow," and the net brought up many tadpoles. Fig. 6 

 shows how much heavier these tadpoles were than those caught only 

 about 5 m away at "West." 



On 15th May, no tadpoles could be seen at "Spawn Site" but 

 some were collected in the net. This also happened at "West." 

 Tadpoles were still numerous at "Sallow," but the algae were turning 

 brown, and had not appreciably extended in area, and no more were 

 seen anywhere else in the pond. 



Reference to Fig. 6 shows that from 8th May to 7th June, the 

 tadpoles at "Sallow" were always heavier than at any of the other 

 collecting points, although after 15th May, the lead they possessed 

 was progressively reduced. On 23 rd May, the algae were quite brown 

 and microscopic examination showed that tliis was due to the for- 

 mation of resting-stages. The collections on 29th May and on 6th 

 June showed nothing remarkable, but on 6th June it was noted that 

 there were still no signs of algae at "West." The wet weather had now 

 begun, and on 12th June there was a sudden change. The water level 

 was now so high that the marshy ends were covered with water. It 

 can be seen from Fig. 6 that a corresponding change had occurred in 

 the tadpole population. "Spawn Site" tadpoles were now the largest 

 in the pond, and at the next collection on 19th June they retained this 

 lead. The "Sallow" tadpoles were now the lightest. In spite of the 

 earlier start to the season, metamorphosis had not yet begun — by this 

 date in 1947 many of the httle frogs had left the pond. On 28th June, 

 the algae had disappeared from "Sallow." Metamorphosed frogs were 

 seen at the next visit on 6th July, and the population of tadpoles was 



