#1: the mystery of the rainforests...

2/1/2014

(from commons.wikimedia.org/)

Hello! I'm Patrick, and this is my blog. I'm an English biology student who's entirely new to blogging (I thought a blogroll was something *completely* different), so I am, genuinely, very sorry for whatever is about to follow. I'm taking to the internet to chronicle my imminent adventures in the rainforests of Central America - into which, in the vague spirit of a bespectacled nineteenth-century naturalist, I will shortly be plunging armed with welly boots and the odd moth-bitten Spanish phrasebook...

The unsolved riddle of rainforests

Nobody knows why the tropics are hyper-diverse. There are more tree species in a single measly hectare of the Amazon than in the whole of North America... It's one of the great unsolved mysteries of ecology, and, excitingly, it's what the project I'll be joining is attempting to answer. As you travel from the poles to the equator, the diversity of life around you burgeons and skyrockets, eventually peaking in the damp, humid, miasmic, thunder-cracking, leech-lurking extravaganzas that are tropical rainforests. Earth is the most complex thing in the known universe, and tropical forests are the most complex things on Earth, so that makes tropical forests the most complex things in the known universe. So why are the most complex things in the known universe the most complex things in the known universe?

Genipa americana (from http://en.wikipedia.org/wiki/Genipa_americana)

Does the answer lie with pests and pathogens?

An irrelevant picture, but I like it. (Wikimedia)

The project I'm joining - a collaboration between the universities of Oxford and Sheffield - is pinning its hopes on an exotic and powerful phenomenon, a process formidably termed 'the Janzen-Connell mechanism'. The J-C mechanism suggests that the hyper-diversity we find amongst rainforest trees arises because there's simply a greater capacity for species to coexist in tropical forests - and it claims that that greater capacity for coexistence emerges from a strange and beguiling interplay between tree species and host-specific pests and pathogens. Around a tree, it imagines a zone where life is hard; let's call it the 'ouch zone'. In the 'ouch zone', any aspiring trees of the same species will suffer from pathogens and herbivores that specialise on that species. Saplings of the same species as the tree at the centre of the 'ouch zone' will be more likely to cop it within the 'ouch zone' than their heterospecific colleagues will be. That's all very sad, but it does mean there's an exciting career opportunity in the 'ouch zone' for seeds of other species - which aren't as affected by those specific pests and pathogens - to grow into mature trees themselves. This means that as a species rises in local abundance, it's members are more likely to die. Therefore, there's a negative feedback mechanism preventing a handful of species from crowding everyone else out. Got all that? The J-C mechanism says that tropical diversity is all about life and death, parasites and predators, tragedy and triumph, and the heart-wrenching woes of adolescent trees in a world that seems weirdly out to get them.

Does water have a role to play?

If you read the last paragraph carefully, you'll notice something odd, which is that it didn't actually explain why the J-C mechanism would be any more likely to operate in tropical forests than in the temperate zone. Why, you cry, isn't Milton Keynes teeming with thousands of species too? The answer is this: for some reason, the J-C mechanism might be operating at crazy levels in the tropics, meaning the capacity for species coexistence is wildly greater in tropical forests.

One of these drivers of the J-C mechanism may be humidity/moisture content/rainfall/dry seasons, that sort of thing. And that's the idea that's behind this project. In dry sciencey language, the first key question is: 'does the intensity of pest pressure, the driving force of the Janzen-Connell mechanism, rise along a latitudinal gradient of increasing humidity?' In human terms, the question is essentially this: 'are tropical forests the most complex things in the known universe partly because... they're damper?'

In the rainforest understory... (Wikimedia).

Oropendola! (Wikimedia.)

Wait a sec... What if climate change affects water?! It might have knock-on effects for the diversity of rainforests...!

Right. So this project is trying to help answer one of the greatest mysteries in ecology. Hurrah! But that's not its only commendable feature. Thanks to humans, Earth is teetering on a precipice, dangerously close to major climate changes. In an era of climate change, what will happen to tropical forests? They are, after all, the most complex things in the known universe, so we had better care. As climates change, humidity is likely to change too, and if humidity is the elusive missing link in the Janzen-Connell mechanism, that could have major implications for the dynamics of tropical rainforests. Knowing how the J-C mechanism works might be rather important in understanding what'll happen to the tropics through this century and beyond.

To Panama!

Panama! (Wikimedia.)

So that, in a nutshell, is why I'm off to Panama. For four months, I'll be enthusiastically counting seeds, spraying fungicide, and, in particular, rearing the larvae of insect seed predators (basically things wot live in seeds). I'll be regularly blogging about it all, including my enthusiastic misadventures in Spanish. I look forward to seeing you here!

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