East Coast - An Ecosystem In A Pitcher
Life in the coastal barrens is tough - and that breeds ingenious adaptations in the animals and plants who call them home. Maybe none more so than the purple pitcher plant, a carnivorous bit of flora who’s unusual digestion gives rise to a whole hidden ecosystem in a few centimetres of water - and incidentally an incredible miniature laboratory for scientists.
EPISODE NOTES
The lichen inserts for this episode were shot on the Rideau Canal, at Davis Lock.
Pitcher plants, especially younger ones, do produce some digestive enzymes to help with breaking down their food, but they produce less and less of these as they get older and still have to rely on their on-board ecosystem to do most of the work.
In 2023, scientists discovered that pitcher plants were able to adjust the scents they gave off to attract particular kinds of bugs.
There will often be one piece of research that has an outsized influence on a given video. In this case, that was Tracey Switek’s beautiful blog post about pitcher plants.
TRANSCRIPT
The coast of Nova Scotia can be a rugged, windy, harrowing place. Cold Atlantic waves crash against massive, sweeping tracts of granite, carved smooth by glaciers and stripped bare of soil by erosive wind and salt spray, leaving us with this eerie, otherworldly landscape.
It’s known as the coastal barrens. And the carpet of plants that clings to it is stubborn, short and stunted. But it also has to be very well-adapted for an unforgiving life.
That adaptation can take a lot of different forms.
Lichens have evolved so many tricks for obtaining nutrients - including dissolving rocks with acid - that they can live directly on the granite.
Plants that do make use of the thin layer of soil that’s available, like blueberry or juniper bushes, deploy wide shallow root systems to anchor themselves and grow small waxy leaves to conserve water.
But then, scattered across the landscape, you’ll also see these: clusters of little maroon umbrellas popping up above the scrub.
They’re the flowers of the purple pitcher plant, which might win the contest for wildest adaptation to life in the coastal barrens.
Faced with so few nutrients available in the soil, they’ve turned to another source: bugs. They’re one of the few carnivorous plant species, like Venus fly traps or sundews. That’s why they hold their flowers so high up on stalks - and why they give off a citrus-y smell - to guide helpful pollinators and make sure they don’t end up in the ‘pitcher’ below.
That pitcher is the really astounding part. It’s built of specially shaped leaves to catch and retain rainwater. The rim is covered in a sweet nectar to attract other bugs. When they land to eat it, the waxy, sloped surface slides them down into the water, and downward facing hairs on the inside of the pitcher keep them there… trapped.
Already, pretty cool for a plant. But that’s barely breaking the surface. Pitcher plants just get more amazing the closer you look.
Because what we’ve got right now is… a bug in some water. How does that translate to this plant getting the nutrients it needs?
That’s where things get really nuts. It turns out there is a whole world in that couple inches of water. A complete, multi-layer ecosystem entirely within the pitcher plant’s pitcher.
That ecosystem is built around three larvae - of a mosquito, a midge and a fly.
They each inhabit a distinct layer. At the top are the more aggressive fly larva who go after the bugs that have just landed in the water. As they tear apart the prey, pieces fall to the bottom where the midge larva go to work on them. And in between, any bits tiny enough to float up - or down - through the middle get picked off by mosquito larva.
And it might seem like they’re all stealing the plant’s meal, but its actually a symbiotic relationship. They break down the pitcher plant’s prey for it, both by tearing it into smaller pieces and, yes, excreting it.
But even that is just one layer of the pitcher plant ecosystem. See, those mosquito larva may be last in line on the larva food chain, but zoom in again and they’re the apex predator in a whole smaller world of critters - rotifers, mites, protozoans, bacteria, all in their own complex web of predator, prey and detrivore, all contributing ultimately to the pitcher plant’s digestion.
Pretty incredible plant. And incidentally, an incredible resource for scientists.
See, ecosystems are really hard to study. They’re chaotic, enormously complex, and impossible to isolate. Meanwhile science needs clean, replicable experiments to prove or falsify hypotheses.
But on an ecosystem level you can’t, say, just take all the elk out of Alberta to see what happens. Or, suddenly double the amount of sunlight while maintaining all other factors. And do it repeatedly to verify results.
Pitcher plants, though, kinda give you that opportunity. They’re obviously not gonna be perfect analogues for any ecosystem, but they provide a tiny experimental world where you can actually say ‘what happens if we remove the apex predator from this system’ or ‘what if we suddenly provide it with double its usual nutrients?’ and usefully extrapolate the results.
After more than a century of study, pitcher plants are still surprising us, and are still capable of helping us answer huge ecological questions - all in just a few centimeters of water.