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An Analysis of Density Effects and Predation in Bufo Americanus Tadpoles
Author(s) -
Brockelman Warren Y.
Publication year - 1969
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1936252
Subject(s) - biology , predation , tadpole (physics) , metamorphosis , ecology , survivorship curve , larva , bufo , midge , odonata , population density , mayfly , nymph , growth rate , cannibalism , predator , population , toad , physics , genetics , demography , geometry , mathematics , particle physics , cancer , sociology
The effects of density on growth and survivorship of Bufo americanus tadpoles and the importance of some predators were investigated experimentally in two small ponds in southeastern Michigan. Tadpoles were raised through metamorphosis at different densities and food levels in screened inclosures placed in the ponds. Most inclosures were open to the natural substratum but others were completely screened to exclude larger predators. In one pond experiment, time of metamorphosis, individual growth variability and mortality were directly related to initial tadpole density, and transformation size was inversely related. The addition of food (natural periphyton on plant litter) produced a density—dependent increase in growth rate. The density—related mortality was correlated with variations in growth rate among pens. Growth rate was correlated with submerged plant cover in the pens. Neither survivorship nor growth was correlated with predator densities. The other pond experiment was characterized by a lack of significant density effects and by high mortality rates. Mortality was correlated with abundance of predators, chiefly nymphs of Odonata and the small leech Batrachobdella picta. Comparison of experimental tadpole densities, growth rates, survivorship and environmental conditions with those of tadpoles in undisturbed environments indicates that the conclusions reached should have relevance to natural population dynamics.