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October 18th, 2017

The Trophic Cascade

BY Christian Ford

What you eat is where you are — that’s the lesson of the trophic cascade.  This catchy term is the handle for discoveries that have rumbled through the life sciences in the past decade or so and they’re pretty revelatory. Trophic comes from the Greek for “nourish,”  and the term is a way of talking about food webs, only differently than we usually do.  The typical conception of a food web builds from the bottom up, assuming that it’s the availability of prey which controls the lives of the apex predators up top.  But the trophic cascade reverses the paradigm, and amazement ensues when you watch what happens when the waterfall of nourishment descends.

The signature example comes from Yellowstone National Park, where wolves were reintroduced to the park after an absence of 70 years.  Park managers didn’t bring back many wolves, but being at the top of the food web meant that the wolves had an outsized impact and particularly on the swarms of deer that had grown during Yellowstone’s wolfless decades.  After a time, all deer were presented with evidence that nibbling the sapling trees in the meadows along the edge of the river was a good way to get eaten. Some deer, distracted by their phones perhaps, kept snacking by the river and were turned into wolf chow.  Other deer, realizing that the rules were now different, changed their behavior, demonstrating a learning impulse which puts them one up on many humans.

The trees, no longer “hunted” by the deer, discovered that they could hang out along the edge of the river, growing larger and digging their roots deep into the bank. Bigger trees meant that beaver reappeared, because they needed the bigger trees to build their dams, which in turn created more habitat for birds, fish, muskrats, ducks, and otters.  Meanwhile, the wolves also reduced the numbers of coyotes, which meant that rabbit and mouse populations soared, which in turn brought more foxes, weasels, badgers, and hawks.  Wolf carrion helped feed the bears, and so did all the new berries now hanging from bushes that hadn’t been nibbled to nubbins by the landscape-consuming deer.  So there were now more bear, too, and they further reduced the numbers of deer, bringing them more in line with historic numbers.

Things really get interesting, though, when we look at the rivers themselves. It turns out that bigger riverside vegetation, along with an the absence of churning hooves, stabilized the water’s edge.  The river, responding to the new reality, dumped less silt into the water, which encouraged the water itself to run faster and clearer, too, much to the delight of fish.  The fast waters cut away the curves of the lazy silty river built by the deer and lo – the rivers of Yellowstone actually changed shape.  In other words, the wolves not only changed the entire animal population of the park, they changed its geography.

The trophic cascade is a sobering demonstration of the profoundly deep and mysterious ways that life works.  Many people, coming face to face with this sort of revelation, tend to feel a sense of wonder and an inescapable certainty that there is a larger order to the world they inhabit, the unseen hand of God or Gaia, depending on your predilections.

But isn’t it, in a way, curious that the trophic cascade came as news to us?  After all, top-down has been the golden rule of human society as far back as the dawn of agriculture and the headlines daily remind us that the powerful call the shots.  But if we combine the lesson of Yellowstone’s wolves with the broken record of the headlines, then a question emerges. What if it’s not just that the rich stay rich and the poor stay poor?  What if the wealthy change the entire social system — the economic system — in a fundamental way.

It’s fairly easy to accept that notion if we look backwards. We have little trouble understanding that the rich and powerful of Babylon shaped their city-state world, styling themselves as gods while compelling the peasants to pay tax in barley.  But we also note that ye olde Babylonian peasant, though oppressed, still had an option.  He could — as Huck Finn almost said —  light out for the territory. Not that far beyond the Babylon city limits, our peasant-on-the-run could find a world where the rules were not the same.  Sure, there was no guarantee that what he found would be better, but it would be different.

This is where the world-reshaping comes in, because we cannot say the same. Globalized trade has been in the offing for centuries now, but it’s taken the homogenizing mixmaster of the internet to truly globalize culture and economy.  Good luck finding the city limits sign these days and good luck again trying to find a different economic and social cascade other than the one where shit rolls downhill, and we are urged to celebrate the fact.

But setting that aside for the moment — not easy, I know — let’s go a little farther and see what happens if we assume that the human trophic cascade isn’t just metaphor, or culturally inherent, but applies completely.

This is a tricky thing for humans of the First World variety, rooted in their certainty that humanity and nature share neighboring abodes and aren’t members of the same family.  But let’s try to push the notion all the way to where the apex-predator-shapes-the-world-we-all-inhabit notion is not about laws and cultural norms, but just the blunt and literal truth.  What if the wolves eat and everyone else’s role is to be on the menu?

A raw deal, I’m sure you’d say, and I’d agree.  But Yellowstone poses awkward questions with its thriving ecosystem.  Surely that’s a sign that — however unfair this may seem to the individual deer ending his days as wolf chow — this is the way things were meant to be.  And if that’s the case, then maybe our problem is not grotesque inequality but really a refusal to adopt a Buddhist “life is suffering” mindset and accept our role in the greater scheme.

What’s interesting, if we look back to Western Culture’s previous organizing principle, religion, is that we used to do just that.  Kings, wars, plagues, famines — all of it was labeled “God’s will” and the survivors trudged on.  But there was apparently a fundamental dissatisfaction with that setup, at least for Western Europe and the cultures that emerged from it.  And that, not to put too fine a point on it, is a fairly profound existential fix, because as soon as you decide that there must be more to life than simply existing, you also discover that thinking that thought makes it impossible to go back to simply existing.  But that’s the road we went down and that’s where we have finally come to, where the toxins of our existential befuddlement now threaten all the other lives that never forgot how to be just what they are.

But as I was saying, how do we know that our current predicament — wolves calling the shots, everyone else catching the bullets — isn’t  exactly how it’s supposed to be and that all our complaints aren’t just the kvetching of a self-aware prey animal refusing to embrace our role?   Well, there’s an awfully big hint in the trophic cascade topped by the biggest animals ever to live — whales.

You’d think that, being huge and eating infinitudes of significantly tinier creatures, whales must be the overlording 1% of the sea and that wherever they go, the vacuum up the all the food and leave the sea less full of smaller things.  That, in fact, has been the operating assumption of fishermen and fisheries scientists for just about forever.  But it’s wrong.

The reason, amusingly enough, is that whales poop.  No surprise there, but here’s one that you likely don’t know — whales may feed at depth, but they return to the surface to flush.  This apparently irrelevant fact is a big deal, because by doing this, whales reverse the nutrient flow in the ocean, where everything tends to sink into the abyss.  That’s life messing physics, whales monkey-wrenching gravity, and scientists have taken to calling it the “whale pump.”  What’s more, whales don’t just pump nutrients back to the surface, they also move them thousands of miles laterally, by feeding in the high, cold, latitudes, and then returning to warmer, less productive seas, to breed.

What the pump most particularly moves is iron, returning it to the surface waters where it is urgently needed by phytoplankton.  These guys are the microscopic plants of the sea, capturing the energy of sunlight by photosynthesis and forming the bedrock of the entire oceanic food web.   The net result of all this, then, is that wherever the whales roam, no matter how much they eat, the sea itself becomes richer in in life, a lot richer in life, the entire food web thriving and burgeoning.   And if that isn’t cool enough, then look at the last little step this particular cascade enables.

When these greater clouds of phytoplankton die, they fall into the depths of the sea, a slow rain of microcrystalline “snow,” made up largely of carbon.  And that carbon stays down there for thousands of years, locked safely away from the atmosphere.  In other words, the great whales aren’t content to reshape mere rivers like the wolves do.  In their eternal orbit between the surface of the sea and its nocturnal depths, whales change the nature of the sea itself and the sea of atmosphere above it and in so doing, they change the climate.

Or rather, they did, before we hunted them to nearly to extinction.  There is even some reason to believe that the age of whaling was part and parcel of how we destabilized our climate, a process already under way when Melville wrote Moby Dick and the fabric mills filled English skies with coal smoke and both of those endeavors funneled their wealth upward to the creatures at the top of their trophic cascades.

All economics and all trade comes down to eating, and the world we live in is — literally, physically, and profoundly, on land, sea, and sky — shaped by those at the top.  Our wolves, the ones who haunt Wall Street, loudly insist that their version of the world is what nature intended.  But the wolves of Yellowstone and the whales of the Great Southern Ocean tell a different story with their trophic cascades, which don’t just rain down hurt on those below the apex — they also rain down life.  So that, I think, is the question, one one question that precedes all the others, the question humans need to ask: does our path through life make the world around us richer in other lives, whatever they be wolf or whale or tree or plankton? Or does it simply enrich ourselves in the form of a wealth that, as Chief Seattle once said, no one can eat.

 

Pix:
Physeter macrocephalus origamius by William Hartman
Phytoplankton (Coccolithophore) by NEON ja
Yellowstone Pack by Will
Sperm Whale and Calf by Oregon State University