Competitive Interactions among Tadpoles: Responses to Resource Level

Abstract

Using experimental populations of Rana clamitans tadpoles, I examined the hypothesis that the nature of competitive interactions among individuals changes in response to the amount and distribution of the food resource. Competitive interactions within populations were dominated by the largest individuals. Large tadpoles outcompeted small tadpoles for the solid food resource. Small tadpoles ordinarily engaged in filter feeding and were thus exposed to relatively high concentrations to parastic yeast, Candida humicola. At lower food concentrations, large tadpoles responded by increasing the amount of filter feeding relative to substrate feeding, which increase the parasite population growth rate. Small tadpoles subsequently experienced a disproportionate increase in their parasite burden which decreased their competitive abilities relative to the large tadpoles. The aspect of the food resource which alters these competitive interactions appears to be the bivarate distribution of food items in time and space. The results of this investigation imply that deterministic models may be inadequate to predict outcomes even in laboratory situations because organism seem to be maximizing their probability of success conditional on their current situation.