Climate change and threesomes: it just gets more complex

Photo Credit: gbohne via Compfight cc

Photo Credit: gbohne via Compfight cc

Growing up in New England you become very comfortable being surrounded by untraditional families and relationships. Brady-bunch-style blended families, with step-s half-s and semi-s are a dime a dozen. I’ve known more than one person who has accidentally dated a double-step-brother (step-parents step-child from previous marriage) and had to ask….is that legal? Turns out it is….at least in Massachusetts.

Meanwhile the younger set is happily redefining what a relationship means. This runs the gamut from: “We’ve been seeing each other for 5 weeks, can I call you my girlfriend?” to “We’ve been seeing each other for 5 minutes, let’s get married!” Relationships also come in all shapes and sizes, from people coupling up in a traditional two, to those who include three, four and even more in their relationship status.

I’ve always been impressed with those who were able to manage these multi-person relationships. I have trouble attending to one other person, I can’t imagine having to remember the birthdays of 2 or 3 others. And then there would be all of their families, and significant others and suddenly I would be completely lost in a web of people. Each time you add a person, you add a layer of complexity. Complexity is difficult for people like me.

It turns out though, that nature is very good with complexity, and the more complexity you add on, rather than making things too difficult to follow, it makes them more interesting to study. This is no more clear than with trophic interactions.

What is a trophic interaction? Well you see, when you are out in nature you tend to be either eating or being eaten. For example a carnivorous lady bug eats an aphid that eats a pepper plant. Yes, if you are the size of a pin head, lady bugs are terrifying, insatiable carnivorous monsters. Be glad you’re not so small.

The interaction between these munchers and munchees are called trophic interactions, and where you are on this food chain is your trophic level. The fact that I mentioned three organisms (lady bug, aphid, plant) means that it was a tri-trophic interaction. Tri, means three. Like tricycle, d’uh.

These kinds of questions get sort of cool when you ask what happens if there is a massive lady bug boom and all the aphids get eaten, do the plants do really well that year? Or maybe there is an aphid boom and all the lady bugs couldn’t possibly eat them all, do the plants suffer? What if all the plants die from a drought, does the system collapse?

And then what happens when you throw another variable into the mix, as will happen with climate change. Well actually with climate change there will be a zillion variables, like increased CO2 and warming temperature and water availability. But one thing we tend not to talk about, which is predicted with climate change, are heat waves. More heat waves.

So what happens if I expose that tri-trophic interaction I mentioned before (evil lady bugs, plump and delicious aphids and fresh, tasty pepper plants) to extreme heat waves. What would you predict? Would the plants just die from the heat wave, leaving the aphids and therefore lady bugs to suffer? Would the aphids get heat stroke, negatively impacting the lady bugs, but helping the plants survive? Would they all get sun tan lotion out and lie out on beach blankets?

These are all great research questions (except maybe the last one), but actually, this threesome, is a little more complex. You see, when there are just aphids and plants, a really simple system, the system can be heavily impacted by a large event like a heat wave. It gets hot, the aphids die, the plant cheers with relief…if it can survive the heat itself. But typically ecosystems are never so simple. More commonly there is an herb (plant), an herbivore (animal that eats the plant) and also, a predator (that eats the herbivore).

Think about it: spiders, tigers, wolves; these are all predators that feed on herbivores in different ecosystems. If you took out the predator, say like we did with the wolf, what do you think will happen to the herbivore, in this example the deer population? Well the deer just start marching around thinking they own the place, eating your flowers, crapping on your lawn….Jerks. Then if there is a major disruptive event, like a heat wave, the impact on the large, uncontrolled deer population is enormous. But if there was already a predator keeping their numbers within reason (whatever that is), then when an extreme event happens the impact is less severe.

The same is true for our predatory lady bugs; take them out of the system and the aphids go wild, so when an extreme heat event happens there is a minor aphid apocalypse. Leave the top predator in and a major heat event has a lesser impact. A little counter-intuitive, I know.

Now we know that most systems are even more complex than this simple tri-trophic interaction with plants being eaten by bugs that get eaten by other bugs that get eaten by spiders that are consumed by birds that are eaten by house cats that are eaten by coyotes that are eaten by your weird neighbor….making the web even more complex. But it’s this complexity that may be protecting the system from extreme events associated with climate change.

So, complexity in some relationships can actually be a good thing, protecting a system from major upheaval and weakening the impact of large disruptive events. Perhaps there is a lesson I should consider for my own life – maybe more complexity in my relationships could help me buffer against great upheaval as well. I’m willing to give it a try if nature predicts it will be better for me….only…who is going to tell my husband? Will you?

Further Reading
Effects of simulated heat waves on an experimental plant–herbivore–predator food chain

Minda Berbeco is the programs and policy director at the National Center for Science Education and a visiting scholar at the UC Museum of Paleontology. She would like to apologize if her post this week is a little incoherent, she is up at the AGU Chapman conference in the Rockies and there is just not a lot of oxygen up here. You can follow all the excitement of the conference on Twitter with #climatechapman

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