Saturday, January 30, 2021

Barreling Towards Extinction: Plant Families in Peril

It's no secret that there are many endangered species among plants, but I was still surprised at how many are threatened by habitat destruction, invasion, and other anthropogenic factors. 

The International Union for Conservation of Nature (IUCN) is the global authority on the status of the natural world and the measures needed to safeguard it. This organization maintains a publicly accessible database of species which have been evaluated called The Red List, which you can view here

In this database, they have categorized species based on several criteria and grouped them according to their risk of extinction. For those species where enough data is available, the categories include:

  • Least Concern - species have been evaluated against the red list criteria and are not threatened or extinct
  • Vulnerable - species have been evaluated with the best data possible and are at high risk of extinction in the wild.
  • Endangered - species have been evaluated with the best data possible and are at very high risk of extinction in the wild. 
  • Critically Endangered - species have been evaluated with the best data possible and are at an extremely high risk of extinction in the wild. 
  • Total Threatened - a sum of the species in the Vulnerable, Endangered, and Critically Endangered lists.

I was reading about an endangered grass  in California, and this prompted me to see how many grass species are lumped into this bucket. So I took a look at the absolute numbers of grass species in the Red List database, subtracted those species which have not been fully evaluated (a grouping called  Data Deficient in the IUCN), and calculated percentages for each of the categories listed above.

It turns out that a bit more than 20% of the Poaceae species in the database that have adequate information are Threatened, which was a number that seemed a bit high to me.

But imagine my surprise when I decided to look at other plant families.

More than 50% of the species in the Orchid, Daisy, Palm, and Cycad taxa are Threatened, with the Aroids coming up to that percentage as well (45%). Indeed, an amazing 63% of Cycads are in the Threatened category! These are shocking numbers to me, and they shine a light on the need for more action in terms of preserving our plant biodiversity.

But before you go into full panic mode, it should be noted that there are caveats to the numbers calculated above.

1. The total number of species listed for many of the taxa in the Red List database is only a subset of the actual number of species in the world.

For example, although the estimated total species in the family Orchidaceae is around 30,000, only around 1400 are listed in the Red List with enough data to make a judgement call on their status (approx. 5%). In the case of the Araceae, only around 7% of the 3700 species worldwide have been fully evaluated, although almost half of that 260 species of Aroids are listed as Threatened.

However, balancing this is the fact that in some taxa, most of the species are already included in the database. For example, it seems almost ALL 300+ species of Cycads in the world are already listed in the Red List, which means these plants are really in dire straits, given that more than 60% are Threatened.

2. There might be a slight bias in the species included in the database towards those that are in peril already. That is, researchers might tend to focus on plants that they believe are in trouble when there are very large numbers of species in the world.

Thus, as more information is gleaned and more species are entered into the database, it is expected that the percentage of  Threatened species will drop lower.

Nevertheless, such data serves as a warning to us to be ever vigilant in protecting our plant biodiversity.

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