Thursday, February 21, 2019

How do you measure biodiversity?

A friend sent me this image that purports to show the number of "vascular plant species per 10,000km". The automatic assumption is that this is a map is a reasonable proxy for biodiversity.

Looking at this map, I am suspicious based on the poverty of biodiversity in Florida and Texas. That just doesn't seem right.

Doing a reverse image look-up yields a website that also lists the number of genus and families per unit area.

Map of Genus diversity. If you expand this map you will find "specks" of super-diversity. They roughly correlate with Ann Arbor, Michigan, Columbus, Ohio...and other college towns. What a coincidence!
For those who are not familiar with the terms: Species is a cluster of plants with more-or-less fixed trait that easily interbreed with each other. Genus are clusters of species that share many fixed traits and can sometimes breed with each other.

Families are one more step up the hierarchy.

The density of species is roughly correlated to the density of Ph.D students needing thesis material.

It is not difficult find enough variation in a widespread population to justify a "new" species. In fact, it was rumored that two botanists "created" two new species of Hawthorn from the same specimen based on the location they were examining. Shade leaves vs. sun leaves and rainy year vs. sunny year will cause significant differences of appearance in many plants.

It is a much, much bigger deal to "discover" a new genus and it generates a serious amount of scrutiny.

Compare northern Georgia and northern Alabama. Look at the map showing the number of species per 10,000 sq-km map and then look at the number of families.

Look at coastal Georgia and Carolinas (current borne species), eastern Texas (flowing out of Central America), central Florida (confluence of sub-tropical and continental) and southeastern Arizona (same as eastern Tx). That is where the rubber hits the road for botanical biodiversity, not California and Calvert, Anne Arundel and Prince George's counties Md.

A tip of the fedora to Lucas Machias.


  1. Interesting point. I've been suspicious of some of the very small species that I've heard recently that are claimed to need protecting; there seems to be no appreciable difference between them and a much large species nearby.
    I read recently about a 'species' of turtle in the Galapagos Islands that was thought to be extinct for over a 100 years, until one was found alive last year. It turns out that only ONE animal had previously been found, dead, in 1906, and that one animal was observed in 2018. They appear to be assuming that the turtles on one island are a distinct species from the turtles on a neighboring island, ignoring the fact that the turtles can and do swim between islands...



Readers who are willing to comment make this a better blog. Civil dialog is a valuable thing.