EFFECTS OF VARIATION IN NATURAL ALGAL AND DETRITAL DIETS ON LARVAL ANURAN (HYLA-REGILLA) LIFE-HISTORY TRAITS

The quality of algae as food for larval Pacific treefrogs, Hyla regill a, varies among algal taxa. Tadpole diets were manipulated in enclosur es in the South Fork Eel River, northern California. Enclosed tadpoles were fed ad libitum one of the dominant filamentous green algae (Clad ophora, Zygnema, Mougeotia, or Oedogonium), the dominant cyanobacteriu m in the habitat (Nostoc), flocculent detritus, or a commercial reptil e/amphibian food. Tadpoles in a control treatment were not fed but had access to seston which deposited in all enclosures. Diet treatment si gnificantly affected weekly growth rates, as well as time to and weigh t at metamorphosis. Tadpoles grew most rapidly on filamentous green al gae with diatom epiphytes and on the commercial food. Tadpoles fed epi phytized Cladophora metamorphosed 27.1% (11.7 days) sooner and weighed 38.9% (70 mg) more than tadpoles fed Cladophora cleaned of diatoms. I n comparison to tadpoles fed Mougeotia, which does not support epiphyt es, tadpoles fed epiphytized Cladophora metamorphosed 37.4% (19.7 days ) sooner and weighed 31.6% (50 g) more. Tadpoles with the lowest growt h rates were those filtering deposited seston or flocculent detritus. Observed changes in life-history traits with diet are assessed in rela tion to models which predict the optimal timing of metamorphosis.