Biodiversity is short for the diversity in biology, from genes to species to habitats. Why do we care about the diversity of genes, species or habitats, rather than just the extent of natural areas, or the number of species?

The famous ecologist G.E. Hutchinson gave a talk in 1959 called "Homage to Santa Rosalia, or Why are there so many kinds of animals?" He recounts how he visited a shrine to Santa Rosalia in Italy, which had a pond. In the pond he observed certain water insects and, like a good naturalist, his mind wandered and he asked himself various questions about them. His famous question was, "..why there should be 2 and not 20 or 200 species [of that type of insect]...in the pond." Why indeed? Answering this question, of why there are more of some kinds of related organisms and less of others--in other words, the diversity of species-- has been a major theme of ecology ever since.

Currently, ecological theory suggests that the higher the diversity of species (many species, of many kinds), the better the ecosystem functions. While every species has a slightly different function, many species have similar functions. This creates redundancy, a bit like a factory that has many lines of production going at once, and its own generator. If something goes wrong in one part of the factory/ ecosystem, there may be another part of the factory/ ecosystem that can take up the slack and keep functioning.

What happens if you have a simple ecosystems with very few species and not of many different kinds? You may be in one of two situations. In some rare cases, your simple ecosystem is almost completely resistant to external shocks (droughts, floods, heat waves, earthquakes, lava flows, and other kinds of natural disasters and climate change impacts)-- because the species in your ecosystem all have basically rock-like resistance to the environment (think water bears). More likely, if your ecosystem has become simple, you are in a precarious situation, one or two natural disasters and extinction events away from ecosystem collapse. Humans are not like water bears. We are highly fragile and destructible, dependent on and interlinked with other species, which is why we think biodiversity is important.

Image credit: By Schokraie E, Warnken U, Hotz-Wagenblatt A, Grohme MA, Hengherr S, et al. (2012) - Schokraie E, Warnken U, Hotz-Wagenblatt A, Grohme MA, Hengherr S, et al. (2012) Comparative proteome analysis of Milnesium tardigradum in early embryonic state versus adults in active and anhydrobiotic state. PLoS ONE 7(9): e45682. doi:10.1371/journal.pone.0045682, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=22716809

--Meredith Root-Bernstein