Rain Forest Insects Eat No More Tree Species than Temperate Counterparts

A study initiated by University of Minnesota plant biologist George Weiblen has confirmed what biologists since Darwin have suspected - that the vast number of tree species in rain forests accounts for the equally vast number of plant-eating species of insects.

"This is a big step forward in the quest to understand why there is so much biodiversity in the tropics," said Weiblen, principal investigator and senior author for the National Science Foundation-funded research. The study is published in the Aug. 25 issue of the journal Science.

The study was carried out in Papua New Guinea and the Czech Republic by scientists from the University of South Bohemia, the Smithsonian's National Museum of Natural History, National Zoological Park, Tropical Research Institute, Comenius University in Slovakia as well as the University of Minnesota.

The researchers, led by Vojtech Novotny of the University of South Bohemia in the Czech Republic, collected insect species feeding on 22 tree species at the Czech and Slovak sites and 22 species in Papua New Guinea. In all, some 850 insect species were recorded.

The research showed that insect species in tropical and temperate forests dine on about the same number of tree species, despite the more diverse menu in the tropics.

"The tropical forest cafeteria offers many more options than the temperate forest," Weiblen said. "Our study confirms that the choices tropical insects make are quite similar to those of insects in less diverse forests of places like Minnesota."

The study rejected an alternative theory that tropical insects are actually picky eaters who prefer fewer host plants than their temperate counterparts.

"Theory predicts that similar species coexist by dividing up resources like food and space," Weiblen said. "The unparalleled diversity of plant-eating insects in the tropics could be explained according to this theory if tropical insects were more choosy than those in temperate forests. But it hasn't been possible to compare what's on the menu until now."

Identical experiments on tropical and temperate insects were unknown until Weiblen developed a technique to control for differences in food plant diversity.

"It turns out that insect appetites aren't all that different near the equator but the tropical smorgasbord brings more species to the table," Weiblen says.