"We also were careful to calibrate any effects against purely environmental differences, such as what one might see if we compared different, naturally occurring densities of guppies in both natural upstream and more crowded downstream conditions," Travis said. "So, our experiment simultaneously compared the ecological effects of guppies of each type in two densities, one double the other. That design enabled us to learn whether the changes we saw in the ecosystem processes were caused by the natural differences in guppy density or the differences in the guppy 'type.'"
"Type" mattered. For instance, because downstream guppies ate more insect larvae and less plant material, they excreted more nitrogen and less phosphorus.
"The combined effects of different grazing and different fertilization patterns served to change algal growth rates, detritus decay rates because guppies can eat the little animals that eat decaying leaves and the overall oxygen consumption rates in the ecosystem," Travis said.
"The evolutionary effects we documented are so large that an ecologist can no longer say, 'Sure, you evolutionary guys can show some effect from genetically based differences, but those effects are small in the big scheme of things.' Well, they aren't small. The changes generated by the new guppy species are at least as great as those found by doubling the density of existing guppies.
"We also show that the standard approach to theory in ecology and evolution, which is to say, 'Let's keep ecological variables constant and study evolution' or 'Let's keep evolutionary variables constant and study ecology,' isn't necessarily a good approximation for reality," Travis said. "We now know that evolutionary effects and ecologi
|Contact: Joseph Travis|
Florida State University