Population ecology of the leopard frog, Rana pipiens pipiens Schreber at Delta Marsh, Manitoba
Eddy, Susan Bates
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Population parameters and various aspects of the life history of the leopard frog, Rana pipiens pipiens, were studied at the University of Manitoba Field Station at Delta Marsh, Manitoba over three summers. Stomach samples contained a wide variety of animals, including tadpoles and frogs of their own species. Empty stomachs were found during cold and cloudy weather, and during migration and breeding periods. Spring migration from the lake to breeding areas in the marsh took place as soon as it was physically possible and breeding occurred immediately. Fall migration seemed to be triggered by a combination of internal and external mechanisms although the weather controlled the intensity of activity on any evening. Tadpole growth varied between sites and between years, probably because of the amount of food available. There are at least three year classes of frogs, but following the fourth summer more than one year class can form a size class - growth is fastest in the second summer, and extremely slow following the third. Females grow faster than males, but the difference is not significant. Although mortality is normally high in the tadpole stage, low water 1evels resulted in even higher mortality. This was probably because of algae toxins and lack of oxygen rather than predation. During the study there was a shift in the size structure of the population due to selective mortality on younger frogs. Unusually heavy ice and north winds following the beginning of the thaw killed younger frogs, which stayed in or near the lake in early spring. By the spring of 1974 there were very few frogs left and most of these were of the largest size class.