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Fact and fiction in tropical forest insect diversity

Beetles: what we know, what we don't know and what we think we know but don't

by Eric Jackson

On March 6 veteran entomologist Nigel Stork spoke at the Smithsonian Tropical Research Institute's (STRI) Tupper Auditorium, with the announced topic "Insect diversity in tropical forests: sorting the fact from fiction."

Dr. Stork, who has his PhD from Manchester, would be good at sorting insects and facts related to them. He was a curator of the insect collection at the British Museum for 17 years, taught at the James Cook University in Australia, and for 12 years managed a tropical resource center in Queensland, where Australia's northeastern jungles stand opposite the Great Barrier Reef. He was in Panama (not for the first time) in between jobs, as he's just about to take over as head of the University of Melbourne's Natural Resources Department.

So has Dr. Stork sorted the fact from the fiction about the biggest issue raised? He noted that Dr. Erwin, working mainly out of STRI in 1982, estimated that there are about 30 million tropical insect species. "My best guess," Stork opined, "is somewhere between five and 10 million species." But he quickly added that a paper he wrote on the subject was rejected for publication.

Insects, you see, comprise about half of all species described in scientific literature, fewer than one million of such in all. But the great majority of species are not described. Of those found in literature, there are as many different beetles as the next three orders of insects combined, about 150 families in all.

Erwin, Stork noted, fogged 19 trees of just one species here in Panama and found some 1,200 species of beetles living on this one kind of tree alone.

From his own four-year study of tropical tree beetles' distribution in Australia, Stork encountered about 29,000 species. In the canopy and on the ground the assortments of beetles are different, although about half of the species don't specialize in any particular part of the tree. There are more rare species up in the canopy than at ground level, but there isn't much difference in the percentages of described versus undescribed species up high or down low.

And what about the seasonality of tropical beetles? It very definitely does exist, with changes in canopy and ground assemblages taking place in phase. Over the years most studies have found that beetle populations are richer in diversity during the rainy season, but Stork found that, contrary to those expectations, more beetle species were found in the dry season.

The rainiest part of the rainy season was the lowest period of beetle activity, but is that a sampling effect, for example by the rains inhibiting flying so fewer individuals getting caught in flying traps? And don't flying traps inherently discriminate against those beetles that prefer to get around by crawling?

And what about the synchronicity in the seasonal changes in beetle populations? Is it about life cycles, disease, predation or migration? Or is that, too, affected by some sampling effect?

Those things need to be looked at, Stork said. You see, when you sort fact from fiction in science, you generate a whole new set of questions for each fact that you establish, or think you establish.

Gender and health
Fact and fiction in tropical forest insect diversity