Interaction of an insecticide with larval density in pond-breeding salamanders (Ambystoma)
BRIAN S. METTS, WILLIAM A. HOPKINS AND JOHN P. NESTOR
University
of Georgia, Savannah River Ecology Laboratory, Aiken, South Carolina,
U.S.A.
SUMMARY
1. Amphibian populations residing in or near agricultural areas are often
susceptible to pesticide contamination. Recent evidence suggests that
the effects of pesticides on amphibians often exceed those estimated in
laboratory toxicity tests because other environmental factors (e.g. predators,
resource abundance) can influence pesticide toxicity.
2. To examine the effects of an insecticide (carbaryl) on two species
of Ambystoma salamanders experiencing the natural stress of competition,
we manipulated chemical concentration (control, 3.5 and 7.0 mg L
-1) and larval density (low and high). We determined the effect
of treatments on snout-vent length (SVL), growth rate, lipid reserves,
time to metamorphosis, per cent survival and percent metamorphosis.
3. Carbaryl negatively affected all response variables of Ambystoma
macuiatum significantly, and significantly reduced survival and metamorphosis
of A. opacum. Increased density significantly influenced SVL,
lipid reserves, growth rate and metamorphosis of A. macuiatum.
4. The effects of carbaryl and increased density on per cent metamorphosis
were nearly additive, but were generally less than additive on other variables.
5. The negative effects of chemical contamination on salamanders were
likely because of pesticide-induced reductions of food resources, as zooplankton
abundance decreased by as much as 97% following carbaryl application.
6. Our study demonstrates the importance of the interactive effects that
chemical contamination and natural environmental factors have on salamanders.
Keywords: Ambystoma maculatum, Ambystoma opacum,
carbaryl, density, insecticide
SREL Reprint #2815
Metts, B. S., W. A. Hopkins and J. P. Nestor. 2005. Interaction of an insecticide with larval density in pond-breeding salamanders (Ambystoma). Freshwater Biology 50:685-696.
