A stable isotope study of a neotropical stream food web prior to the extirpation of its large amphibian community.
Abstract:
Rapid and massive amphibian population declines
have been reported
throughout upland areas of the Neotropics. The abundance and species
richness of Neotropical amphibian communities suggest that losses of
this magnitude are likely to have strong effects at the ecosystem
level. To improve understanding of the implications of their loss we
used stable isotope analysis to examine trophic relationships in an
ecosystem in which amphibians arc dominant in a second-order forest
stream at 750 m asl in Parque Nacional Omar Torrijos Herrera, Panama.
We analysed delta C-13, delta N-15 and C:N ratios of major biotic
components (basal resources, invertebrates, amphibians, fish and
reptiles) in the stream and of the adjacent riparian food web. Tadpoles
(mean delta N-15 = 4.49 parts per thousand) and adult amphibians (mean
delta N-15 = 5.45 parts per thousand) were intermediate links in the
aquatic and terrestrial food web respectively. High delta N-15
signatures identified fish as top predators in the aquatic food web and
snakes and the toad Bufo as top predators in the terrestrial food web.
Isotopic signatures clearly distinguished between trophic groups of
tadpoles: microbial feeders (Centrolenidae, delta N-15 range =
0.91-3.05 parts per thousand), herbivores (Rana and Hyla, delta N-15
range = 4.74-5.15 parts per thousand) and neuston feeders (Colostethus,
delta N-15 range = 5.31-6.40 parts per thousand). Dependence on
autotrophic production was indicated by enriched signatures of carbon
isotopes in pool dwellers versus those that reside in faster-flowing
sections of the stream. High nitrogen concentrations in detrital matter
(average 0.8%, C:N = 10.3) suggested that grazing tadpoles enhanced
nitrogen fluxes and improved the quality of organic matter available to
detritivores.
Verburg, P., Kilham. S. S., C. M. Pringle, K. R. Lips, D. Drake, and M. Whiles. 2007. A stable isotope study of a neotropical stream food web prior to the extirpation of its large amphibian community. Journal of Tropical Biology 23: 643-651.
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