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More bang for your bugs: quantifying the arthropod species of a tropical rainforest

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Most multi-cellular species on Earth are arthropods living in tropical forests. Yet, given the difficulties involved in just counting them, we know very little about their exact numbers – even at the scale of a single forest.

A University of York biologist is part of an international team which has completed a new study of the rainforests of Panama which provides an unprecedented level of detail on the diversity and distribution of arthropod species from the soil to the forest canopy.

Our results confirm that small areas in the tropics – here just 23 square miles – can indeed harbour as many species as entire temperate countries

Dr Olivier Missa

Dr Olivier Missa, of the University’s Department of Biology, was a member of IBISCA-Panama, an international project led by Dr Yves Basset, from the Smithsonian Tropical Research Institute. The project sampled, sorted, catalogued, and finally estimated that a 6,000 hectare forest hides a total of around 25,000 arthropod species – a figure vastly outnumbering that of better-studied organisms. The study is published in Science.

To sort the arthropods, a massive collaborative effort was necessary, involving a total of 102 researchers from 21 countries. During 2003-2004, the field team spent a total of nearly 70 person-years’effort sampling the rainforest canopy from cranes, inflatable platforms, balloons, climbing ropes through forest layers, as well as crawling along the forest floor to sift soil, and trap and bait arthropods. Over the ensuing eight years, the team sorted and identified 130,000 arthropods, to a total of more than 6,000 species.

By scaling up the diversity values obtained from twelve intensively-sampled sites, the research team was able to calculate that the rainforest reserve harbours in excess of 25,000 arthropod species.

“To put this number into perspective, the United Kingdom, a country with one of the most complete species inventories in the world only has about 26,000 species of terrestrial arthropods,” says Dr Missa who contributed to data analysis for the project.

“Our results confirm that small areas in the tropics – here just 23 square miles – can indeed harbour as many species as entire temperate countries.”

“This high number also implies that for every species of vascular plant, bird or mammal in this forest, you will find 20, 83 and 312 species of arthropods, respectively,” explains Dr Basset.

“If we are interested in conserving the diversity of life on Earth, we should start thinking about how best to conserve arthropods,” adds Dr Tomas Roslin, from the University of Helsinki.

“What perhaps surprised us the most was how large a fraction of all species in the forest was detected in our smaller samples”, says Dr Basset. “Another exciting finding was a close correspondence between the species richness of plants and that of both herbivorous and non-herbivorous arthropods.”

Image: Jürgen Schmidl releasing a cloud of insecticide in the forest understorey (R. Le Guen)
Image: The elephant beetle (Megasoma elephas) crawling in the understorey (N. Winchester)
Image: Dawn Frame and Alexey Tishechkin in the crane gondola netting insects attracted to flowers of Nectandra purpurascens (J. Schmidl)
Image: The canopy raft in position at San Lorenzo (R. Le Guen)

“By focusing conservation efforts on floristically diverse sites, we may then save a large fraction of arthropods under the same umbrella. Further, this strengthens past ideas that we should really be basing estimates of global species richness on the number of plant species,” adds Dr Roslin.

Further information

  • The paper 'Arthropod Diversity in a Tropical Forest' by Y. Basset et al is published in Science.
  • IBISCA-Panama
  • Department of Biology
  • Banner photo shows a "psychedelic" species of grasshopper, Arachnoscelis magnifica,
    Tettigoniidae (Photo by M. Leponce)