Analysis of the crowding effect in Rana pipiens tadpoles

Rana pipiens tadpoles were grown at four densities in each of three series. Retardation due to crowding was seen despite the presence or absence of feces. Statistical analysis shows retardation due to crowding to be a function of effective density, possibly mediated by behavioral or social factors, more importantly than by diffusible products of the tadpoles. Although previous work has assumed the growth‐inhibiting factors of “conditioned water” (water occupied by a population of tadpoles) to be identical with the cause of the crowding effect, we have found that the crowding effect operates relatively independently of these growth‐inhibiting factors.