My first year of graduate school, I set out to complete an independent field project in the hill country of Western Massachusetts. In all my clever, pre-doctoral planning, I did not account for an unexpected outbreak of the hungry, hungry tent-caterpillar that summer.
These caterpillars completely took over the forests of the Berkshires, consuming any greenery they could get their little munchy mouths on. They covered everything from top to bottom, leaving tacky streams of silk between trees. I learned not to touch anything, sit anywhere or walk with my mouth open (seriously). There were so many of them that the sound of their chewing and the pitter patter of their scat hitting the forest floor became a deafening echo. Gross.
A few weeks before the caterpillars made their cocoons, friendly flies arrived (no really, the common name is “friendly fly”). These flies are known for laying their eggs in caterpillar cocoons, using them as incubators for their little babies. When the larvae hatch, they eat their way through the caterpillars, leaving the shell of caterpillar corpses lining trees. If you happen to trip and grab a tree for support after the flies have made their way through, you’ll end up with a handful of mushy orange caterpillar squish. The thought still makes me sick. You’re welcome.
The lesson of this story though is not to gross you out, but really to demonstrate the importance of timing between species in ecological systems. The timing of the flies’ arrival was extremely important. Can you imagine if they had arrived after the caterpillars had pupated and started to mate? What would the effect have been the next year? Could the forest survive multiple years of caterpillar invasions? What would all that caterpillar poop do to the soil?
This is the sort of thing that ecologists get totally worked up about (poop included). The timing of life cycle events (when trees flower, when caterpillars pupate) is actually fundamental to ecological systems. Since these organisms don’t have calendars, watches or Siri to direct their activities, many use temperature as an indicator of when to start growing, migrating, hatching, laying etc. This has been observed in all sorts of organisms, from plants to butterflies to birds to newts (1, 2, 4).
‘Great’, you might think, ‘Spring is coming earlier, so what is the problem?’
Well, if all the plants and animals in the forest are shifting their life cycle events earlier, you will be a sore loser in the game of life if you are the one species who can’t keep up. This inability to shift your life-cycle events when all the other organisms are doing it is called an ecological mismatch.
Basically in the natural world, keeping up with the Joneses (or the caterpillars, the flowers, the other birds) is exceptionally important. Imagine if you will, a teenage yellow-bellied marmot whining to its mom, “everyone else is doing it…” but instead of responding with the typical “if everyone jumped off the bridge, would you too?” the marmot mom would say, “oh yeah? Get your bungee cords honey, because we got to get jumping!” Not jumping in this case means not eating and this could definitely impact your survival. In the case of the marmot, they have not only jumped the bridge, but swam the river, made it to shore, completed a 10K and caught the new Borne movie (i.e. climate change has done them well). Too far-fetched an analogy?
How about a more straightforward example—researchers found that between 1988 and 2005, caterpillar and insectivorous bird (i.e. birds that eat caterpillars) hatching dates have advanced, but the big-ass sparrow hawks that eat the insectivorous birds have not advanced their hatching dates (“hatching dates” are when the baby birds hatch, you dig?). This means that the little insectivorous birds are happily readjusting when they are having babies to match when there are the most caterpillars, but the big, scary carnivorous sparrow hawks are not (5). Sucks to be the sparrow hawk.
In the case of some animals, adapting to a changing climate and “getting there early” is greatly to their advantage. This is the case for frog-loving newts (no, not frog “loving”, it’s newts who eat frog eggs). These newts have started entering ponds earlier than before (due to increases in temperature) and have a buffet of frog eggs (who have not shifted their laying or hatching behavior) to munch on. This is great for the newts, but pretty terrible for the frogs (1,3). And since frogs eat bugs that annoy me when I’m hiking, I’m sort of sad about this.
So it turns out your freaky yoga teacher was right. Timing is a central part of living systems and many organisms are dependent on this for their survival. Not all of them will be able to adapt to the temperature changes that come with climate change, and this puts them at great risk.
Being Humvee-driving, frog-baseball-playing, marmot-loving homo sapiens, this might not bother us too much. But since you now know that all of these systems are connected, one little frog out of sync or one bird species down could have major impacts for the organisms themselves and us in the end.
The future is looking very mismatched, and that is not going to be good for any of us. Having survived one epic caterpillar invasion in the forests of western Massachusetts, I just don’t think I can handle the next. And after hearing my description, could you?
Minda Berbeco has a PhD in Biology from Tufts University and is a science writer in the Bay area. In addition to the caterpillar apocalypse during her first field season, she also had to contend with mice in her sleeping bag, a disgruntled field assistant, chewing-gum sized mice babies in her cabin, 16-hour work days, ticks in unexpected places (behind the ear?!?! Really?!?!) and head lice (thanks mice!) The next time someone calls ecologists a bunch of lazy hippies, she encourages you to accidentally punch them in the nose.
(1) Ecological responses to recent climate change
(2) Warmer springs lead to mistimed reproduction in great tits (Parus major) (It’s a bird, your pervert.)
(3) Amphibian breeding and climate change
(4) Climate warming, ecological mismatch at arrival and population decline in migratory birds
(5) Climate change and unequal phenological changes across four trophic levels: constraints or adaptations?