TOXIC BOG WATER IN NORTHERN MINNESOTA PEATLANDS: ECOLOGICAL AND EVOLUTIONARY CONSEQUENCES FOR BREEDING AMPHIBIANS

Breeding amphibians in the boreal peatlands of northern Minnesota encounter a mosaic of water quality: acidic Sphagnum bog sites (pH 5.0). I investigated the ecological and evolutionary significance of bog water for breeding amphibians in the peatlands of northern Minnesota.;I compared the utilization of toxic bog and non-toxic fen sites by breeding peatland amphibians. I found that amphibians favor fen breeding areas although fen sites are less abundant. The degree of bog breeding varies among species. Bog and fen breeders differed in behavioral characteristics, but appeared similar in demographic traits. The available data suggests that fidelity to natal fen sites is an important factor in the observed patterns of bog utilization.;I compared the bog water and acid (H(,2)SO(,4) acidified medium) tolerance of wood frog embryos from a southern Minnesota marsh habitat (where bogs have not been an important component of the environment for the last 10,000 years) and a northern Minnesota bog community ((TURNEQ) 3000 years old). The bog population was more tolerant in all tests. These results support the hypothesis that wood frog populations in northern Minnesota bogs have adapted to some degree to toxic bog environments. Data from other studies indicates that high acid tolerance (hatching success down to pH 4) is a geographically widespread and relatively uniform species trait. The acid tolerance of the wood frog may preadapt this species for bog environments and explain why the wood frog is the most bog water tolerant species in northern Minnesota peatlands.;In laboratory and field experiments I determined the bog water tolerance of peatland amphibian embryos and larvae. None of the peatland amphibian species successfully survived through metamorphosis at toxic bog sites. The wood frog (Rana sylvatica) was the most bog water tolerant species and the only species to reproduce at poor fen sites. Fen water was a suitable developmental medium for all species. The toxicity, stability, abundance, distribution, and age of bog water sites indicate that bog water is an important source of selection operating on peatland amphibians.