30 CoUrge of Forestry 



Animals on Different Kinds of Bottom. Another feature 

 brought out by the investigation was the relative abundance 

 of animal life on the different kinds of bottom. Sand bottom 

 (Fig. 11) was found to be the richest in number of indi- 

 viduals and boulders the poorest. If the sand be valued at 

 100 per cent, the other kinds of habitats will stand as fol- 

 lows: Sandy clay, 87 per cent; clay (Fig. 12), 66 per 

 cent: gravel, 57 per cent; mud (Fig. 13), 42 per cent; and 

 boulder. 36 per cent. Of the areas examined in the vicinity 

 of Lower South Bay, the sandy bottom between Frenchman 

 and Dunham Islands was computed to be the richest of all 

 the shallow areas examined, averaging about 110 million 

 individuals per acre. The poorest area in the vicinity of the 

 bay in animal life was found to be the boulder bottom (Fig. 

 14) along the shore, which averaged but four million indi- 

 viduals to the acre, or less than 4 per cent of the population 

 of the sand bottom. The reason for this paucity of the ani- 

 mals is the exposed character of the environment and the 

 small amount of plant food present. 



Herbivorous and Carnivorous Animals. The great pre- 

 ponderance in number of animals feeding on plants (herbiv- 

 orous) and 011 fine ^particles of decaying plant material 

 (dust-fine detritus) on the bottom and suspended in the 

 water, over those animals that feed upon other animals 

 (carnivorous) is strikingly shown by these lake studies. 

 The herbivorous animals number about 7,743 million indi- 

 viduals while the carnivorous animals are calculated to 

 number not more than 23 million individuals, or about 3/10 

 of one per cent. This fact is important when it is remem- 

 bered that the herbivorous or plant-eating animals are 

 producers of flesh from vegetation and debris and the, 

 carnivorous animals are consumers of materials used more 

 extensively as fish food. But few fish (aside from the Carp) 

 feed extensively on vegetation. One of the significant facts 

 brought out in these investigations is that the presence of 

 filamentous algse in abundance profoundly affects the inver- 

 tebrate animals, providing a food supply of sufficient amount 

 to meet the requirements of a large population of small 



