... Beetles and Biodiversity...
by Infocostarica Staff

Ever since we first developed rudimentary speech, our species has been giving names to other organisms. There was obvious survival value in being able to transmit information such as, "Saber-toothed tiger behind palm tree," and not have it misinterpreted as, "Sure is a pretty palm tree."

With technological advances during the last 150 years permitting access to every conceivable portion of the globe, from the highest mountain peaks to the deepest ocean trenches, and the adoption of a worldwide standardized labeling system, taxonomists have now provided scientific names for more than 1.5 million of Earth's organisms. And still, by many estimates, this colossal task of cataloguing our fellow creatures is far from completion.

One poignant example to illustrate this assumption is the research carried out by Dr. Terry Erwin of the National Museum of Natural History. In the early 1980's, he and a team of researchers sampled arthropod diversity (insects, spiders, mites, centipedes, etc.) in the canopies of rainforest trees in Panama and Peru. They used a powerful motorized sprayer to send a cloud of insecticide up into the treetops. Traps were laid out just above the ground to catch a portion of the intoxicated invertebrate fallout.

When the specimens were sent, group by group (e.g., mosquitoes, dragonflies, jumping spiders, etc.), to specialists for identification, the results were hundreds of previously undescribed species. The tallies for the beetles alone led Erwin to produce some staggering calculations.

Beetles, the largest order of insects, account for about 40% of all known arthropod species. Assuming that this percentage would hold as new species of invertebrates are discovered, and given the number of new kinds of beetles that came plummeting out of the rainforest canopy in his experiments, Erwin extrapolated that the true total of arthropods could be in the neighborhood of 30 million species!

Whatever the final number may be -- and it's not the sort of thing that we can expect will ever be known with complete certainty -- it's only logical that tropical rainforest insects should account for a significant percentage of the total. This is due in large part to the diversity of plant life found in these warm and humid environments.

Plants, excluding algae and fungi, make up about 18% of the world's currently named organisms. And nowhere are there more types of plants to be found than in a tropical rainforest. Not only are the trees themselves more diverse than in any other habitat on earth, but they come festooned with epiphytes and vines which add to the species total.

Among insects, roughly half feed on living plant tissue, the rest are scavengers, predators, or parasites. As a group, those that feed on plants extract their sustenance from the roots, trunk, stems, bark, shoot tips, leaves, flowers, fruits, and seeds, or in short, from every portion of their hosts. Some insects are quite specific about the species and part of the plants they consume, others are generalists.

The result of this is that the wealth of plant life in tropical rainforests can support an enormous number of arthropod species. Returning to the Erwin study, they discovered 163 species of beetles (not to mention all the other kinds of invertebrates) living in the canopies of just one tree species. Multiply that by the hundred other tree species to be found on an average hectare of tropical rainforest and you've got a lot of bugs!