Biodiversity metrics on ecological networks: demonstrated with animal gastrointestinal microbiomes

Biodiversity has become a terminology familiar to virtually every citizen in modern societies. It is said that ecology studies the economy of nature, and economy studies the ecology of humans; then measuring biodiversity should be similar with measuring national wealth. Indeed, there have been many parallels between ecology and economics, actually beyond analogies. For example, arguably the second most widely used biodiversity metric, Simpson (1949)’s diversity index, is a function of familiar Gini-index in economics. One of the biggest challenges has been the high “diversity” of diversity indexes due to their excessive “speciation”—there are so many indexes, similar to each country’s sovereign currency—leaving confused diversity practitioners in dilemma. In 1973, Hill introduced the concept of “numbers equivalent”, which is based on Renyi entropy and originated in economics, but possibly due to his abstruse interpretation of the concept, his message was not widely received by ecologists until nearly four decades later. What Hill suggested was similar to link the US dollar to gold at the rate of 35 per ounce under the Bretton Woods system. The Hill numbers now are considered most appropriate biodiversity metrics system, unifying Shannon, Simpson and other diversity indexes. Here, we approach to another paradigmatic shift—measuring biodiversity on ecological networks—demonstrated with animal gastrointestinal microbiomes representing four major invertebrate classes and all six vertebrate classes. The network diversity can reveal the diversity of species interactions, which is a necessary step for understanding the spatial and temporal structures and dynamics of biodiversity across environmental gradients.