The Hawaiian archipelago is a group of volcanic islands in the Pacific ocean. [Figure 4.1] shows the relative locations of five of these islands. Table 4.1 shows the size and age of these five islands and the total number of Mecyclothorax ground beetle species and their species density, on each island. Data for the island of Maui is shown as two distinct regions, West and Haleakalā. This is because they formed at different times from two separate volcanoes. Table 4.1 island area / km² age of island / million years total number of Mecyclothorax species species density / number of species per km² Hawai'i 10433 0.4 30 0.003 Lãna'i 364 1.3 3 0.008 Maui (West) 443 1.3 27 0.061 Maui (Haleakala) 1440 1.1 116 0.081 Moloka'i 673 1.9–1.8 43 0.064 O'ahu 1545 3.7–2.6 20 [Figure 4.2] shows a ground beetle of the genus Mecyclothorax. All the beetle species of this genus on the Hawaiian archipelago form a monophyletic group, descended from one original colonising species that reached Maui from Australia.