Tadpole Ripples
Streams feel impact of tropical frog extinctions
Tadpoles can leave ripples in a stream – even when they are gone. With a deadly fungus causing catastrophic declines in tropical frogs, many streams are losing their tadpoles. The loss of the wrigglers can subtly but significantly reorder stream ecosystems, find researchers who are studying the ecological aftermath in Panama.
The chytrid fungus has become a disaster for tropical frogs, rapidly driving dozens of species to extinction. The carnage, however, has given ecologists a rare opportunity to find out what happens when tropical streams suddenly lose an important player. As they transform into frogs, tadpoles become ecosystem engineers, grazing on algae and stirring up detritus.
To see how other stream life responded to tadpole losses, ecologist Checo Colon-Gaud, now at Georgia Southern University in Statesboro, and colleagues spent two years studying four 100-meter long stream reaches in central Panama. Two of the segments had lost most of their tadpoles in 1996, after the chytrid fungus reached the area; the other two experienced “a massive decline” during the second year of the study. In each segement, the researchers measured the abundance of macroinvertebrates (such as visible insects), biomass, nutrient flows and other key ecosystem indicators.
In the stream that lost its tadpoles during the study, the researchers saw no major changes in overall macroinvertebrate abundance or biomass. But they did see changes in how different community members fared. Algal mass spiked, for instance, presumably because of reduced grazing pressure. In contrast, the researchers saw a decline in the mass of invertebrates that feed by “shredding” detritus , perhaps because the tadpoles helped process dead leaves, a major food source. Predatory species also declined, perhaps because their prey could now hide in algae and sediment once cleared by tadpoles.
The short-term findings “indicate that the loss of tadpoles in these streams affects basal resources” and remaining consumers, and can “translate into changes in ecosystem processes and function, even during the early stages of amphibian declines,” the researchers conclude in a paper published earlier this month in Journal of the North American Benthological Society. “However, despite the loss of an entire consumer group, these systems did not yet show signs of a complete collapse.” The focus now, the researchers say, is studying how these streams respond over the long term to the loss of their tadpoles. – David Malakoff
Source: Colón-Gaud, C., Whiles, M., Lips, K., Pringle, C., Kilham, S., Connelly, S., Brenes, R., & Peterson, S. (2010). Stream invertebrate responses to a catastrophic decline in consumer diversity. Journal of the North American Benthological Society, 29 (4), 1185-1198 DOI: 10.1899/09-102.1
Image © Jolanta Dabrowska | Dreamstime.com
