GENERAL LIFE HISTORY OF THE TADPOLES 



31 



Lower Parkfield Pond 



(a) 1947 (Fig. 8). This pond is almost circular, and about 21 m in 

 diameter. In some places it shelves to the edges, but it is an ornamental 

 pond in a public park and artificial rocks have been placed round parts 

 of it, and there is a stone wall on one side. It is almost surrounded by 

 tall trees that greatly affect the ecological conditions. There is little 



MG 

 500 



400 



300 



200 



100 



10 20 30 



MAY 



9 19 29 9 19 29 8 18 28 7 17 27 7 '7 

 JUNE JULY AUGUST SEPTEMBER OCTOBER 



Fig. 8. Lower Parkfield, 1947 



Except for the fortunate few that metamorphosed about the middle of June, 



this was a year of disaster. From the beginning of July onwards to October, 



there was no growth, and the population consisted of emaciated animals in 



ever decreasing numbers. 



sunshine and the autumn leaves fall into the pond, decaying slowly 

 enough to form a substratum of rotting vegetation all the year round. 

 Duckweed {Lemna) covers the pond, and for much of the time forms 

 a continuous canopy. Some upright phanerogams of various species 

 grow in the shallow margins, but there are never any conspicuous 

 patches of algae. In wet weather the pond receives the overflow from 

 another pond, Upper Parkfield, and it is possible that it is fed by 

 springs, for the water level alters very htde with the rainfall. Frogs 

 lay their eggs near the point of entrance of the htde stream, not always 

 in the same place but certainly always in the same region of the pond. 

 In 1947 the pond was not visited (nor indeed known) until iSth May, 

 when a dense aggregation was found at "Spawn Site." Dispersal had 



