PARENT SESSION
Oral Session #39: Invasions: Effects of invaders -- Aquatic, marsh, riparian. Presiding: C. Kolar.
Wednesday, August 8, 2001. 8:00 AM to 11:45 AM. Madison Ballroom C.
Introduced fish increases survival of introduced bullfrogs.
Adams, Michael1, Pearl, Christopher1, Bury, R.1, Nebeker, Alan2, 1 2
ABSTRACT- We hypothesized that nonnative bluegill (Lepomis macrochirus) are facilitating the survival of nonnative bullfrogs (Rana catesbeiana) through an indirect effect mediated by dragonfly larvae (Aeshnidae) in western North America. Aeshnid larvae were capable of high predation rates on bullfrog larvae in laboratory experiments and reduced survival to zero in field enclosures with either native fish (Richardsonius balteatus) or no fish. Adding bluegill increased survival of bullfrog larvae from zero to 20% when aeshnids were present but had no effect when aeshnids were absent. Field surveys at 57 permanent ponds in Oregon and Washington revealed higher bullfrog abundance and lower predaceous macroinvertebrate abundance when nonnative fish were present but this pattern was weak. We conclude that bluegill facilitate survival of bullfrog larvae in PNW ponds but field surveys suggest that other factors may have more important effects on bullfrog distribution and abundance.
KEY WORDS: invasion, Rana catesbeiana, facilitation, ponds