Gravity's Rainbow

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The crisis: put down the pruning shears


Part of applying to graduate school is figuring out who I want to work with and what questions I want to try to answer.  To do this, I’m reading a lot of papers.  I’d hate for all this paper reading to keep me from blogging, so I’ve decided to share some of the more interesting papers I come across.

The best paper I’ve read this week is almost 10 years old, but is still quite relevant, especially for the International Year of Biodiversity.  Michael Novacek and Elsa Cleland summarize the current threats to biodiversity and detail our options for trying to preserve biodiversity.  I don’t think much of what they cover will be surprising to any of you.  However, seeing all of the threats outlined with connections drawn between them alongside our (very few and very daunting) options for saving biodiversity clarified the situation for me.  Hopefully it’ll do the same for you.

I’ll be doing several posts over the next week or so addressing the three main parts of the paper: How bad is the biodiversity crisis? What’s causing it? and What can we do?

It’s a well written and fairly accessible paper and is publicly available, too, if you’d like to read it yourself.  The main benefit to reading my summary of it is that I’ll be including pictures.

The Biodiversity Crisis: How Bad Is It and Why Do We Care?

The biodiversity crisis is very, very bad.  Species are going extinct much more quickly today than they did a long time ago and the extinction rate is only expected to increase if we keep on with business as usual.   Up to 40,000 species go extinct in the rainforest alone every year.  A quarter of all of mammal and flowering plant species are currently at risk of extinction along with more than a tenth of all birds and a third of amphibians. Many of the large carnivores we so admire and who play absolutely critical roles in their/our ecosystems are beyond hope.

extinction rates

Past, recent, and future extinction rates

You may not really care about extinct begonias, but living through a mass extinction event (think The Land Before Time) isn’t pleasant for anyone, except perhaps the fungi and scavengers.  Of course, you’ve heard all this before.  Right now you’re expecting me to go off about how we rely on biodiversity for clean water, clean air, and other ecosystem services.  If you’ve read this blog long enough, you’re likely wondering how long it’s going to take me to pull out that Jared Diamond quote about the airplane.  Not this time!

This paper makes a point I’d never considered:  When we cause extinctions, we don’t just change the earth now, we change it forever.  The “recovered” earth won’t be an earth we recognize.

Every time a species goes extinct, it’s like chopping a twig off of the tree of life.  At normal extinction rates, just a few twigs are lost every year, but extinction rates now aren’t anywhere normal.  The evolutionary future of a world with a tree of life like this:

A good tree of life

is very, very different from a world with a tree of life like this:

The future tree of life

Losing any species could have a very dramatic effect on the future of life on Earth.  Consider this phylogenetic tree:

In a phylogenetic tree, the nodes (branching points) represent the most recent common ancestor.  A long time ago, the most recent common ancestor of chickens and people wasn’t a branching point yet – it was just a leaf on the tree.  Imagine if that ancestor was wiped out by dinosaur farming (or maybe an asteroid).  What would our world look like now?  Would there be people, or even mammals? What about birds?  Could they (we) have evolved from a closely related species of that ancestor?

This brings up a second point related to biodiversity conservation: We have to prioritize species for conservation.  If the most recent common ancestor of chickens and humans had gone extinct but a closely related species survived, there’s a chance that evolution would have proceeded along similar lines – maybe we would have still gotten birds and mammals.  If all of the closely related species had gone extinct, too, evolutionary history would for sure be VERY different.

So in order to limit how much we change the evolutionary future of the earth, we need to save as much taxonomic variety as we can.  That is, we have to focus on keeping the tree branches intact – not the little twigs and leaves at the end.

Perhaps if we’d acted sooner we wouldn’t be in a position of having to choose to save 1 species from a small branch over potentially hundreds from a large one.

Novacek, M. (2001). The current biodiversity extinction event: Scenarios for mitigation and recovery Proceedings of the National Academy of Sciences, 98 (10), 5466-5470 DOI: 10.1073/pnas.091093698

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