Erwin and scott used an insecticidal fog to knock down insects from the top section of a l. seemannii tree. the researchers identified over 900 species of beetles among the individuals that fell. erwin also projected that this entire tree from top to bottom is host to about 600 arthropod species that are unique to this tree species and not found on any other tree species. there are approximately 50,000 species of tropical trees. although it could not be entirely accurate, what would be the best way to estimate the total number of arthropod species?