Premium
Interspecific Competition between Tadpoles of Rana pipiens and Rana sylvatica: An Experimental Field Study
Author(s) -
DeBenedictis Paul Alfred
Publication year - 1974
Publication title -
ecological monographs
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.254
H-Index - 156
eISSN - 1557-7015
pISSN - 0012-9615
DOI - 10.2307/1942308
Subject(s) - leopard frog , tadpole (physics) , interspecific competition , predation , biology , competition (biology) , ecology , intraspecific competition , habitat , rana , amphibian , physics , particle physics , endocrinology
The wood frog, Rana sylvatica, and the leopard frog, Rana pipiens, occur sympatrically over much of northern North America. Within this area the two appear to show habitat separation. Previous studies have given circumstantial evidence that competition leading to the habitat separation might be occurring between tadpoles of these species. In a pond on the University of Michigan's Edwin S. George Reserve, tadpoles were raised in enclosures where species composition and density of experimental populations were controlled. A preliminary experiment was designed to determine the influence of density and mixing of species on tadpole survival and production of biomass. In a second experiment, in addition to density, food and predation levels were manipulated to determine which were influential in the responses observed. The behavior of tadpoles in the 2 yr was markedly different. In the first experiment tadpoles behaved as if there were no limiting carrying capacity to the pond; mean survivorship was about 14%. There was no evidence of competition. In the second experiment the pond's carrying capacity appeared to be near the lowest density level tested. Both species reacted strongly to each other, behaving like ecological equals. Tadpole survivorship proved sensitive to both predation and food levels. At high predation levels, the effect of mixing species was reduced. Although mixed populations performed less well than those raised alone, I was unable to alter the interaction by adding food to experimental populations even though intraspecies competitive effects were reduced. The original concept of this ecological system was that it would be controlled either by food or by predators. The results of both experiments suggest that this concept was erroneous. Both factors act jointly. The role of food must not be studied without recognition of the extent to which predators can change the impact of tadpoles on their food supply, and vice versa. The results of the first experiment suggest that interspecific competition for food under natural conditions can eventually be demonstrated, because food levels can be sufficiently increased to negate the influence of one species on the other. As ecological systems are feedback systems, future field studies must become more experimental if they are to reveal the underlying mechanisms determining the structure and function of ecosystems.