A team of 102 scientists spent a year surveying a small area of the San Lorenzo rain forest in Panama to count the number of species of arthropods living there. After collecting 129,494 specimens—using nets, traps, shovels, tree-climbing harnesses, helium balloons, and other creative gear—it took the team eight years to sort and identify the arthropods. By comparing the number of arthropod species that were common among the 12 plots sampled, the researchers estimated that the total number of arthropods in the whole San Lorenzo forest is 25,000 species. To come up with this estimate, what's one assumption the researchers had to make about the forest?