Why Bugs Outnumber Us (And Other Mammals) 312 to 1

A headcount of arthropods, a group that includes insects, arachnids and crustaceans, finds that these creatures outnumber mammals -- including humans -- by a ratio of about 312 to 1.

The scrappy organisms also outnumber plants 17 to 1, the study, published in the latest journal Science, suggests.

"There are different reasons to explain this," project leader Yves Basset told Discovery News. "They are small and can make a living out of nearly everything, including other arthropods, decomposing matter, plant tissues, etc."

Basset also pointed out that often bug larvae don't compete with adults since they feed on different foos resources.

Basset is scientific coordinator of the CTFS Arthropod Initiative at the Smithsonian Tropical Research Institute. To better understand arthropod diversity, he and 102 other researchers looked for the organisms in the San Lorenzo forest reserve of Panama.

Bugs tend to thrive in tropical rainforests, but the population at this particular reserve in Panama is thought to be average. The scientists chose to work there because the Smithsonian has a canopy crane and other devices at the site that facilitate access to everything from the canopy forest to the substrate below.

Using this crane, inflatable platforms, balloons, climbing ropes, and by crawling on their knees to get a better look, the researchers sorted and identified 130,000 arthropods. These represented more than 6,000 species.

By scaling up the diversity values obtained from twelve other intensively sampled areas, the team calculated that the 23.2-square-mile rainforest reserve harbors an excess of 25,000 arthropod species. These calculations, in turn, contributed to the estimated ratios comparing numbers of arachnids to plants and mammals.

Basset thinks that these ratios hold true for cities as well, and may even skew higher in favor of arthropods at urban settings.

"The mammal fauna in cities is rather depleted, but not necessarily that of arthropods," he explained. "For example, a small urban park may not host many mammal species, because it may be a too small area to sustain species requirements, such as food and living space. However, let's say you have 10 species of trees in this park, then they may well support as many as 200 arthropod species, according to our data."

Humans tend to view insects mostly as being detrimental. They can at times spread disease and destroy crops.

"But we forget that these represent only a few species in comparison to the whole of arthropod biodiversity," Basset said. "The majority of insects live in forests and are responsible for the maintenance of these forests via the different services of pollination, decomposition and herbivory. In addition, many arthropods are efficient predators or parasites that suppress the levels of herbivores."

Outbreaks of pests do not exist in tropical forests, he pointed out, suggesting that arthropods help to keep ecosystems in balance.

These organisms additionally "represent a formidable, but untapped, reserve of DNA, genes and molecules -- again about 20 times more species-rich than plants from which we nevertheless get most of our medications," he continued. "Who knows what may be concealed in these arthropod molecules and how we could use them? We also need to discover most of these species/molecules before they disappear from Earth."

This latest study and others indicate that we may be sharing the planet with about 6 million arthropod species. Out of these, we only know about 1 million, with the rest  and many others possibly threatened by pollution, habitat loss, and other human-related problems.

Read more at Discovery News