What do you think is the biggest recent conceptual advance in ecology?

What new idea has emerged recently that is likely to revolutionize ecology?

Of course, it depends in part on how you define “recent”. I’ll intentionally leave that vague here. I’d say that the concept of trait-mediated effects has already revolutionized ecology, but I don’t know that it counts as recent. The Werner and Peacor review of TMIIs is from 2003, so this idea isn’t new enough to count as recent in my book.

Instead, I think my answer to this question would be the idea the microbes associated with larger organisms (that is, the microbiome) are what’s really driving much of what we observe out in nature. A series of papers on aphids and their parasitoids provides a good example, I think. As a beginning grad student, I read this 1995 paper by Henter and Via showing differences between aphid genotypes in their susceptibility to a parasitoid wasp. It was a really neat result, and showed clear differences between aphid genotypes. But then, when I was finishing up grad school, this 2005 paper by Oliver et al. came out showing that that variation in susceptibility was actually due to bacterial symbionts carried by the aphids. Whoa! That was neat. The hosts weren’t really in charge; their microbes were instead. And then it got even crazier (in a good sort of way) when it was later shown (in this 2009 paper by Oliver et al.) that, actually, those bacteria weren’t in charge, either – what was really controlling resistance were phage carried by the bacteria. So, in the end, the susceptibility of an aphid to attack by a wasp is determined by whether its gut microbes carry a phage. How cool is that?

The finding that susceptibility to parasites is controlled by microbes has been found in other systems, too (e.g., bumble bees, frogs). How general is it? It’s too early to know, but people now routinely think about the role of commensal microbes in determining disease susceptibility and tolerance, which is a pretty huge shift. This includes in humans, too. The human gut microbiome affects all sorts of things: two great, accessible reviews are this NY Times piece by Michael Pollan and this one for National Geographic’s Phenomena site by Carl Zimmer.* This knowledge is affecting how we treat people (fecal transplants are a very effective treatment for people suffering from recurrent C. difficile infections) and I think is probably one of the most promising avenues for trying to get people to stop overusing antibiotics. If you knew that taking a course of antibiotics increased your risk of debilitating diarrhea or might favor obesity (antibiotics are used as a “growth promoter” in agriculture), you’d think twice before taking them, right?

People who work on plants have been focusing on the role of mycorrhizal fungi for a while now, but, even there, fundamental breakthroughs are still occurring. A prominent recent example is this recent paper by Averill et al., which found that the type of mycorrhizal fungi that dominate an ecosystem determines soil carbon storage, with very important consequences for the global carbon cycle. There’s also a lot of interesting recent work being done on how soil microbes that are associated with plants influence a plant’s ability to tolerate heat and drought (as reviewed here).

Even behavior can be controlled by microbes, as reviewed in this recent Ezenwa et al. article (which also lays out a lot of interesting avenues for future research on the microbiome and animal behavior). As one example, Drosophila mating behavior was influenced by commensal bacteria, as shown in this Sharon et al. study. There’s evidence that human behaviors and mental health are also influenced by the gut microbiome, which has the potential to influence how we treat things like anxiety and depression.

All of which is to say: I think the role of the microbiome in mediating ecological processes and interactions is the recent advance that is in the process of revolutionizing our field. I also think the links between the human microbiome and health are fascinating and have the potential to strongly influence how we treat infections and chronic diseases.**

What about you? What do you think is the biggest recent conceptual advance in ecology?

Postscript: After putting this in the queue, Jeremy, Brian, and I had a brief email exchange related to what counts as a ‘conceptual’ advance. You could argue (as Jeremy originally did) that a ‘conceptual’ advance would be something that is rooted in theory, which this isn’t. But, while I agree that that might often be the case, I think the microbiome is something that, while empirically based, has fundamentally changed how we view the natural world. That, to me, is a major conceptual advance; we think about the world differently now that we know about the microbiome.

* Both of those focus primarily on the gut microbiome, but there’s also work on the lung microbiome (including asking whether it might influence the risk of asthma), the vaginal microbiome (which seems to influence the risk of preterm birth, HIV, and HPV), and the skin microbiome.

**I’m teaching a class this semester on how ecology and evolution are relevant to human health and disease, so this is a topic I’ve been thinking about a lot.