The team assembled data representing 500 species of caterpillars, ambrosia beetles and fruit flies in the undisturbed lowland rainforest of the Sepik and Ramu river basins in Papua New Guinea.
They collected insects and plants from eight study sites across 75,000 square kilometres of the contiguous forest and noted the variation in species makeup among the different sites.
Most previous research has focused on diversity "hot spots," such as upland rainforests in the foothills of the Andes, where steep gradients in elevation, temperature, rainfall and other environmental factors boost diversity by creating diverse habitats within a short distance.
Such change in a region's species makeup between sites is called beta diversity: some rainforests have steep environmental gradients and high beta diversity.
However, a large proportion of the world's remaining rainforests are lowland forests in New Guinea, Borneo and the Congo and Amazon Basins, and many researchers have speculated that such lowland rainforests also would have high beta diversity, though this has not been rigorously tested.
The new data showed low beta diversity across the study area for all three groups of insects as well as for plants, indicating that species tended to be widespread and the biological communities changed very little even across large distances.
"Some spend their entire lives on a single plant, but they've got wings. They may not want to fly, but they can if they need to," said Scott Miller from the Smithsonian Institute.
The insects also showed limited specialization in the plant species they fed upon, in contrast to the common assumption that tropical species tend to be highly specialized.
The study appears in the August 9 issue of the journal Nature.