The Space Factor in the Growth Rate of Tadpoles

There are numerous environmental variables which directly and independently effect the growth rate of tadpoles. The principal factors are, (1) temperature of the medium, (2) amount of available food, (3) amount of radiant energy through light, (4) amount of surface and available oxygen, (5) amount of accumulated excretory wastes, (6) amount of bacterial growth, (7) amount of available volume per individual, (8) amount of available space per individual, (9) amount of forced or stimulated exercise, (10) presence of growth inhibiting substances, X-substances, or autotoxins. In any experimental work involving tadpole growth rate, all of these variables must either be eliminated or controlled. Of all of the variables listed above, the space factor has not been adequately recognized or evaluated in respect to aquatic forms. According to Allee ('31), Hogg ('54) was the first to note the limiting effect of volume on the growth rate of aquatic forms; Semper ('74, '81) suggested that this retardation of animal growth might be due in part to the mechanical disturbances conditioned by crowding; DeVarigny ('94) suspended glass tubes measuring 2 to 3 cm. in containers of various sizes, the tubes being closed over the bottom with muslin. In each tube he placed a single specimen of Lymnamea stagnalis and concluded from results that the growth variations depend on total volume, surface area, and the accumulation of faeces, rather than space. Crabb ('29) stated that food, foul media, and crowding all effected the growth rate of these pond snails. In respect to the tadpole, with which this paper is concerned. Yung ('85) stated that the dwarfing of tadpoles in crowded conditions was due to insufficient aeration; Bilski ('21) found that frequent changes of water or crowding would retard the growth rate of tadpoles of Bufo and Rania esculenta. A corollary to crowding is an increase in the number of frequency of contacts, and it was to this stimulated exercise that Bilski attributed retardation in growth rate. On the basis of these observations, and those of Semper on snails, Bilski devised the following formula to express growth as inversely proportional to group stimulation (see Allee, '31, p. 115, for derivation)