72 ECOLOGY AND LIFE HISTORY OF THE COMMON FROG 



10. Many algae have characteristic smells, perceptible even to the 

 dull human senses at a distance from a pond. It follows that the smell 

 of a pond is specific, in the sense that it is something not found in 

 nature except in a pond, and any particular smell is found only in a 

 few ponds out of many that may be in the area, and then only at 

 certain times. It is detectable at a distance. 



At the time (1935) I first stated this hypothesis, the evidence for it 

 was not very strong, but at least it was an improvement on the others 

 existing at the time. It is now my intention to continue with the 

 description of the life of the frog, leaving it to the readers, with oc- 

 casional reminders from me, to decide whether the later evidence 

 confirms or conflicts with the original hypothesis. If they decide that 

 it conflicts, then I hope that any alternative suggestions that they can 

 think of will be at least as good a fit. They must certainly not be at 

 variance with the facts of the field. 



Distribution 



Distribution is a term with many shades of meaning. Systematists 

 use it to describe the areas within which the species may be found, 

 even if these are as large as whole continents. The ecologist is interested 

 in finer divisions, such as the different geological regions within a 

 country, or even in the way a species distributes itself between two 

 ponds in the same field. Ultimately, it may well be that the large area 

 is merely the sum of many such small ones, fitted together as a mosaic, 

 so that a country contains frogs because it contains ponds that provide 

 suitable living conditions for the frogs. I therefore begin with an 

 account of the distribution of frog-ponds in a small area (Savage, 1939). 



The area lay on the borders of Middlesex and Hertfordshire, and 

 covered about eighty square miles. Within this area, 92 ponds wxre 

 kept under observation over a period often years. None were observed 

 for the whole of this time, for most of the observations were made 

 between 1934 and 1938, although less systematic observations were 

 maintained for another t\venty years afterwards, and some of the 

 ponds were loiown for twenty years before. No attempt was made 

 to include every pond, although the most intensively studied area was 

 thoroughly searched and probably none were missed. In the other 

 parts, accessibility was the main reason for choosing them. There is no 

 good reason for supposing that accessibility was related to the ecology 

 of the ponds, so that the sample could be regarded as typical, even if it 



