Graduate Thesis Or Dissertation
 

Size variation and food habits of larval bullfrogs, Rana catesbeiana Shaw, in western Oregon

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  • An investigation was made of the factors which cause differences in growth rates and transformation size of bullfrog tadpoles under natural conditions. Tadpoles and algal samples were collected from two.adjacent farm ponds of similar size during the eighteen months of the study. It was found that the tadpoles in one pond transformed earlier and at a significantly greater size than those in the other pond. Temperature and genetically determined differences were shown not to contribute to the size differences. Analysis of food in the guts and in the ponds together with feeding experiments provided no evidence that the quality of the food was a contributing factor, nor was the "crowding effect" demonstrated. Lack of sufficient food in one pond was the major contributing factor in stunting tadpoles in that pond. Mortality was higher in the pond with insufficient food. The advantages accruing to those tadpoles in the pond with adequate food were offset in part by a limited die-off in early summmer which was possibly caused by the combined effects of decomposing vegetation, low oxygen tension, and the saprophytic fungus, Saprolegnia. Bullfrog tadpoles fed non-selectively on algae with one exception: Chara was never found in any tadpole gut, even though that alga was the dominant plant in one pond. Vascular plant material may have been a starvation food. Spawning occurred from May to August, and most tadpoles transformed the following summner between July and September. Apparently there was no growth from December to early April, although tadpoles continued to feed.
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