ORIGIN OF FOOD SUPPLY. 17 



THE ORIGIN OF THE FOOD SUPPLY OF CAVES. 



Cave existence, reduced to its simplest terms, is the securing of food and the 

 meeting of mates in absolute darkness. Food is so scarce that no large preda- 

 ceous animals have taken up their abode in caves, hence the largest cave animals, 

 such as the cave fishes, have no enemies aside from parasites and disease germs. 

 Of the cave fishes Chologaster reaches a length of but (>2 mm.; Typhlichthys, 

 55 mm.; Troglichthys, 55 mm.; Amblyopsis, 135 mm.; Litcifitga, 104 mm., and 

 Stygicola, 152 mm. All are insignificant in size. 



The density of the population of any cave, other things equal, is inversely pro- 

 portional to the size of the cave. No food is generated in caves by the growth of 

 plants. Directly or indirectly all food consumed in a cave must be imported. 

 It may come in through various openings ; usually there are only one or two open- 

 ings of any consequence: (a) the "entrance" in a dry cave, (l>) the entrance and 

 point of inflow of the stream in a wet cave. That cave is bust supplied with 

 food per square yard which has the smallest area over which the limited supply 

 must be distributed. There is, of course, a great difference in the amount of food 

 carried in through different openings. An entrance sloping upward naturally will 

 not admit as much decaying vegetation as one sloping downward. A narrow 

 crack through which water may enter a cave will not admit as much as a large 

 opening, through which in times of flood the water may carry tree trunks. These 

 matters equalized, I may repeat that that cave is best supplied with food per square 

 yard which has the smallest area over which the limited supply entering a given 

 opening must be distributed. The density of the fauna varies as the amount of 

 food, and hence, other things equal, inversely as the size of the cave. 



AGE OF CAVES IN RELATION TO THE VARIETY OF CAVE FAUNA. 



Desired lines of research are the relation of the abundance of the cave fauna 

 to the age of the particular cave and the comparative degree of adjustment of 

 the animals to caves of different ages. We have in North America a series of 

 caves reaching from Howe's and other northern caves in the glaciated region to 

 the Ohio Valley caves near the edge of glaciation, and the caves of Texas and 

 Cuba never affected by glaciation. 1 



Howe's Cave in central New York is exceedingly poor in animals, the Texas 

 caves are as correspondingly rich, but no detailed comparison has been made. It 

 is also known that the Ohio Valley cave salamander, Spclrrpcs niticiillcanda, has 

 well-developed eyes, that the Missouri salamander, Typhlotriton, has degenerate 

 eyes, and that the Texas salamander, Typhlomol^r, has very much more degenerate 

 eyes. The degree of degeneration seems here coordinate with the age of the cave. 

 Also that the Missouri blind fish has more degenerate eyes than those of the Ohio 

 Valley. In a general way the older caves appear to have more intimately adapted 

 or more profoundly modified forms than the newer. But here again we lack 

 entirely a detailed study. 



1 Shaler, 1875, estimates the age of the Kentucky caves at between 750,000 and 2,000,000 years. He further 

 maintains that, during the glacial epoch Kentucky was populated by an Arctic fauna and that the cave fauna was 

 not derived from this, but from the present fauna of Kentucky, "since the glacial period." I agree with him that 

 the present cave fauna of Indiana and Kentucky was derived from or developed concomitantly with the present 

 epigean fauna, but am in doubt about the nature of the fauna during the glacial period. 



