iNaturalist can be used to compare biodiversity in different locations.
To do this, it is important to allow for different search effort in different areas: for example, a search of the middle of the Amazon might not return many species, not because there aren't many, but because people haven't observed them.
For the U.S., we will assume that search effort is at least somewhat comparable. We will also look at total observations and divide them by total species to get some idea of the effort required to document a new species in that area.
We decided to investigate my home town in Washington State, Alexandra's home town in Ohio, one of our favorite places: Maui, and our current home in Arizona.
A 100 km search radius includes most of Puget Sound, the Olympic mountains, and Seattle.
A 100 km search radius includes most of central Ohio creeks, woodlands, agricultural lands, and all of Columbus OH.
A 100 km search radius includes canyons and mountains between Flagstaff and Phoenix.
A 100 km search radius includes all of Maui as well as ocean channels and nearby islands.
Summary Table
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According to this analysis, Washington is most biodiverse, followed by Ohio, then Arizona, and in last place is the island paradise of Maui.
Island biogeography teaches that islands, although unique for their level of endemic plants and animals, should be deficient in overall biodiversity if there hasn't been enough time for biodiverse taxa to colonize or evolve on the island. This seems to be the case with Maui, which is especially depauperate in insects, given its tropical location.
Arizona, despite its diverse environments, is significantly lacking in Fungal diversity, which could be due to the arid climate.
The American Midwest, with its perfect seasonal growing climate, is remarkably biodiverse, and would probably surpass Washington if this search had included a more varied part of the Midwest with more mountains and/or rivers and lakes.
Washington tops the list as most biodiverse, probably because of the presence of diverse environments, with everything from alpine mountain tops to ocean kelp forests, and everything in between. This is despite the lower number of insect species compared to a lower latitude place like Ohio.
A caveat to this entire analysis is revealed by the Total Observations in each area and the resulting Observations per Species. While I had assumed that search effort would be equivalent across the US, it is evident that many more people are using iNaturalist around major cities like Seattle and Columbus. Arizona is more sparsely populated and has many less observations, and Maui, despite the huge numbers of tourists, is even less populated. This means that is only takes 20 or 27 new observations (on average) to observe a new species in Maui and Arizona, respectively, while it takes 47 or 72 new observations in Ohio and Washington, respectively, to observe a new species. So even though Washington has the most observed biodiversity in iNaturalist, it may be easier to find new, previously-unobserved biodiversity in Maui or Arizona.
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