Microhabitat Selection and Growth Rate: A Comparison Between the Western Toad (Bufo boreas) And the Spotted Frog (Rana luteiventris)

Abstract

Bufo boreas is a species of toad that has been undergoing extreme larval mortality. Several anthropogenic factors are known to aid in the decline, but less is known about the behavioral patterns and microhabitat influences on the decline. Tadpoles of Rana luteiventris and B. boreas were observed in the wild and data for temperature and depth selection were gathered over a three-month period. Tadpoles of B. boreas selected warmer waters and varied their depth, while tadpoles of R. luteiventris were shown to be more variable regarding temperature selection and less variable regarding depth selection. Even though the tadpoles of B. boreas migrated to inhabit warmer waters, they did not complete metamorphosis until nearly a month later than R. luteiventris. Their more rapid development suggests that they are more adapted to saturating the landscape by occupying a larger number of ponds, while B. boreas is limited to sites large enough to allow for the daily migration from deep to shallow waters. In many areas, these large sites are disappearing for a variety of reasons. Microhabitat selection, in combination with the anthropogenic mechanisms, is a likely contributor to the decline of B. boreas.