A bug’s life: more than 15,000 species of arthropods on one hectare of rain forest

FAU researchers discover unexpected diversity of arthropod species

Approximately 25,000 species of arthropods live on 6000 hectares of rain forest – more than 60 percent of these can actually be found on only one hectare. This is one of the results of the international project ‘Investigating Biodiversity of Soil and Canopy Arthropods – IBISCA’, in which researchers from Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) teamed up with experts from various countries to examine the diversity and distribution of arthropods (the name meaning ‘joint legs’) in forests in tropical as well as milder climates. The research results were published in the journal Science with the title ‘Arthropod Diversity in a Tropical Forest’ (Basset et al., Dec 2012) on 14 December, 2012.

In addition to the core team, a total of 102 researchers were involved in the project and spent altogether 24,354 worker-days between 2003 and 2005 collecting arthropods according to a certain protocol. They have since then identified an impressive 129,494 arthropods from various orders. These current results are based on the research conducted at San Lorenzo National Park in Panama. Until now such projects have been carried out in Panama, Australia, Vanuatu, and France. One such project is currently underway in New Guinea, and there are numerous subprojects in other countries. From the ground to the tree tops, the researchers covered every square centimetre on twelve sample areas within the rain forest, each 400 square metres in size – about the size of a small one-family plot of land. In the process, the scientists found exactly 6,144 species of arthropods. Using different calculation models, they arrived at a total sum of approximately 25,000 arthropod species in the entire 6000-hectare forest. A remarkable fact is that, according to the scientists’ extrapolations, more than 60 percent of these species can be found on as little as one hectare, meaning there is an immense diversity in a very small area. However, FAU researcher Dr. Jürgen Schmidl says it is important not to be misled by these findings: ‘Even though we have observed an incredibly diversity of species on only one hectare of rain forest, it would not suffice to protect only one hectare of rain forest to preserve this diversity: over the course of time, the individual species move around different areas within the entire forest, for example because they follow their food supply,’ the researcher explains. ‘Like mammals, arthropods require what is known as a minimal area – depending on the resources they need. In other words, the entire forest area needs to be preserved to ensure their survival.’

In the calculation models used, the diversity of plant species found in the respective sample areas served as an excellent explanation for the diversity of arthropod species, and this goes for the herbivorous as well as the non-herbivorous species: the researchers were able to show that, in order to get reliable data on species diversity, it is vital to determine the many different groups of arthropods since the individual groups (beetles, cicadas, spiders, etc.) have different diversity patterns. Beetles, for instance, are known to be a megadiverse group with very many different species – if extrapolations were limited to this group, it would lead to an overestimation of species diversity.

Another interesting aspect is the relationship with plants and other groups of animals: on a local level, San Lorenzo National Park has at least 17 and at most 20 arthropod species for every one of its 1294 types of vascular plants. With birds, the ratio is 306 to at least 71 and at most 83 kinds of arthropod. For the 81 mammal species, there are as many as between 270 and 312 arthropod species. On a global level, the results of the research project support current extrapolations stating that arthropod diversity is at approximately 6.1 million species; these are based on models with comparable patterns of beta diversity and guild diversity.

The original article ‘Arthropod Diversity in a Tropical Forest’ by Yves Basset et al. was published in the journal Science 338, 1481 (2012); (DOI: 10.1126/science.1226727)

Further information:

Dr. Jürgen Schmidl
Phone: +499131 85 28076 (Laboratory)