Distribution and Diversity
Beetles are by far the largest orders of insects, with 350,000–400,000 species in four suborders (Adephaga, Archostemata, Myxophaga, and Polyphaga), making up about 40% of all insect species described. Even though classification at the family level is a bit unstable, there are about 500 recognized families and subfamilies. One of the first proposed estimates of the total number of beetle species on the planet is based on field data rather than on catalog numbers. The technique used for his original estimate, possibly as many as 12,000,000 species, was criticized, and was later revised, with estimates of 850,000–4,000,000 species proposed. Some 70–95% of all beetle species, depending on the estimate, remain undescribed. The beetle fauna is not equally well known in all parts of the world. For example, the known beetle diversity of Australia is estimated at 23,000 species in 3265 genera and 121 families. This is slightly lower than reported for North America, a land mass of similar size with 25,160 species in 3526 genera and 129 families. While other predictions show there could be as many as 28,000 species in North America, including those currently undescribed, a realistic estimate of the little-studied Australian beetle fauna's true diversity could vary from 80,000 to 100,000.
Patterns of beetle diversity can be used to illustrate factors that have led to the success of the group as a whole. Based on estimates for all 165 families, more than 358,000 species of beetles have been described and are considered valid. Most species (about 62%) are in six extremely diverse families, each with at least 20,000 described species: Curculionidae, Staphylinidae, Chrysomelidae, Carabidae, Scarabaeidae, and Cerambycidae. The smaller families account for 22% of the total species – 127 families with fewer than 1000 described species and 29 families with 1000–6000 described species. So, the success of beetles as a whole is driven not only by several extremely diverse lineages, but also by a high number of moderately successful lineages. The patterns seen today indicate that beetles went through a massive adaptive radiation early in their evolutionary history, with many of the resulting lineages flourishing through hundreds of millions of years to the present. The adaptive radiation of angiosperms helped drive the diversification of beetles, as four of the six megadiverse families of beetles are primarily angiosperm-feeders: Curculionidae], Chrysomelidae, Scarabaeidae, and Cerambycidae. However, even without the phytophagous groups, lineages of predators, scavengers, and fungivores are tremendously successful. Coleoptera are found in nearly all natural habitats, including freshwater and marine habitats, everywhere there is vegetative foliage, from trees and their bark to flowers, leaves, and underground near roots- even inside plants in galls, in every plant tissue, including dead or decaying ones.
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