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
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
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
"In this context, I have difficulties understanding the
enthusiasm of the public for the search for extra-terrestrial life," Basset
said. "Are we not wasting dollars on a doomed quest, whereas with a fraction of
these funds, we could easily, as our study indicates, unveil a substantial
amount of the Earth’s biodiversity before it is too late?"
Top photo: Scarab beetle (Megasoma elephas, Dynastinae) in the understory of the San Lorenzo forest. Credit: Thomas Martin, Jean-Philippe Sobczak & Hendrik Dietz, TU Munich. Middle Photo: Dawn Frame and Alexey Tishechkin in the crane gondola netting insects attracted to flowers of
Nectandra purpurascens. Credit: Jürgen Schmidl, Laboratory Copyright: University of Erlangen.