The world in a pitcher plant
Provincial flower key to climate study
The ant crawls up the outside of the pitcher-shaped leaves, is drawn inside the “pitcher,” lured by nectar to its death. Decomposing, its body ultimately provides nutrients for the carnivorous sarracenia purpurea — the provincial flower of Newfoundland and Labrador.
The flower’s leaves contain a tiny world, where ants are really not the only things to die, and more than just the flower is given nourishment.
Ecologist Aaron Ellison was able to see pitcher plants up close in this province in 1982. He was in Gros Morne at the time, as part of a vacation around Atlantic Canada, but didn’t know the species would become a centerpiece of some of his work as an ecologist. Specifically, they became key to investigations aiding scientists’ understanding of rapid change, of climate change.
Ellison is now a senior ecologist at Harvard Forest, a research centre on 4,000 acres in Massachusetts and a department in Harvard University’s faculty of arts and sciences. His branch of biology is focused on the interactions between different organisms, and between organisms and their environment.
“What I study is how systems, ecological systems, fall apart under a variety of pressures … and then how they reassemble themselves into something new,” he told The Telegram during a phone interview this week.
Along with Jennie Sirota at North Dakota State University, Nicholas Gotelli at the University of Vermont and Benjamin Baiser, also at Harvard Forest, Ellison was part of an investigation into ecological “tipping points,” leading to a 2013 paper on the subject: “Organic-matter loading determines regime shifts and alternative states in aquatic ecosystems.”
The team used pitcher plants for the study.
Pitcher plants collect rainwater, and they collect prey, but they also hold other things — bacteria, protozoa, microscopic animals (bdelloid rotifer) and maggots (Diptera larvae). They all interact, together making up a food web in a complex, micro-ecosystem (the same way a lake would be a larger, complex ecosystem).
“When I was looking around for good experimental systems to study these kinds of questions with, of course you gravitate to coral reefs or mangrove forests where I was working, or something that I can see and work with that’s big,” Ellison said, before adding, “I don’t have that many lifetimes.”
Studying the world inside a pitcher plant, as opposed to a lake, or something larger, offers the benefit of fast life cycles, faster turnover. Essentially, it’s the benefit of time.
“If we were studying lions or wildebeests on the Serengeti, or if we were studying lynx and snowshoe hares in tundra, or if we were studying moose and trees on Newfoundland, you have to study these for 10, 20, 30, 40 years to really understand the dynamics of the system, because the generation times are pretty long, of these animals,” Ellison explained.
“The generation time of a bacteria is 20 minutes. The generation time of a mosquito is a couple of months. And so we can get the same kinds of dynamics that we get in big animal food webs, we can get (them) in pitcher plant food webs in a tenth or hundredth of the time. So we can actually watch these events unfold in my lifetime, instead of across my lifetime, or multiple lifetimes.”
It doesn’t hurt that humans don’t bother much with the tiny world inside the pitcher plant. When it comes to being a subject of study, there’s less fretting (read: permitting) than there would be with, say, an entire lake.
“Every pitcher is like one lake, and I can do an experiment on that pitcher, then I have lots and lots and lots of replicates, so that I have good power in my experiments, good statistical power, to actually detect facts,” Ellison said.
Settled on the system to use, the team put some theories — largely based on mathematical modelling or study of single organisms — to the test.
The theory centred around what a system should look like as it approaches a tipping point, or period of rapid change, moves through it and then settles in another state.
One of the things it says is you should see, when in one state, a relatively low variance.
“So that this year should look a lot like last year. Of course, it’s going to be (somewhat) different. We always say climate is what you expect and weather is what you get, because there’s always some random fluctuation in it, but that random fluctuation should be relatively small,” Ellison explained. “As you’re approaching a tipping point, the random fluctuations get much bigger.”
He suggested thinking of a bell. When rung, there’s movement, it sounds loudly and vibrates, but then less and less, the sound dying off until it disappears and the bell settles.
“With the pitcher plant system, we’ve been able to actually show it. We’ve been able to say: if you do something, in this case give it too much prey to eat and give it too much nutrients, that we can induce a regime shift in the system,” he said, referring to some of the measurable changes noted in the study paper. “And the dynamics of that change really shows you go from low variability, through high variability, back to low variability, in ways that are very close to how it is predicted mathematically.”
Beyond supporting the basic theory, Ellison’s team has looked for markers that might help in detecting and identifying these ecological tipping points. They’ve looked at what might be required, in terms of time, for complex ecosystems to complete their change, to settle, even after stressors stop.
Imagine it in the context of climate change — if humans stop all emissions tomorrow, how many generations before the world might settle again?
On the other hand, beyond the study, Ellison has noticed just how fast change can hit a complex ecosystem.
“I continue to be surprised the systems tip as quickly as they do,” he said.
“Things happened much faster than we expected in the pitcher plant system. And I think, by extension, when things are changing in this way on a climate scale, or on a planetary scale, my hypothesis is they’re going to go much faster than we expect.”
More recently, Ellison has completed research focused on ant colonies — again using smaller systems to explore the issues facing the larger world.