Fieldwork in Aspen, Colorado
Fieldwork in Aspen, Colorado

In our latest Insight, Pierre Gauzere, a postdoctoral researcher at the LECA (CNRS/Grenoble Alpes University), talks about his new paper, Vacant yet invasible niches in forest community assembly.

About the paper

What’s your paper about?

Our paper is about the existence and emergence of vacant niches in communities: Do vacant niches exist? How can we detect them?  Under which community assembly processes are they more likely to emerge?

What is the background behind your paper?

The paper focuses on the active debate about the saturation of ecological communities. A large part of ecological theory has historically argued that species interactions lead to the saturation of niche space, and therefore that there is little or no “free” space left for species occurring outside of the community. On the other hand, many recent studies support the view that niche space is largely unsaturated, meaning novel species could fit into empty niche space, while niches occupied by existing species do not necessarily have to shrink.

How did you come up with the idea for it?

Assembling the team at Arizona State University
Assembling the team at Arizona State University

When I began my postdoc with Dr. Benjamin Blonder at Arizona State University in 2018, I was thinking about the fact that we have a lot to learn from “what is missing” in biodiversity patterns. This “missing biodiversity” is linked with the concept of dark diversity and functional hypervolume holes. Because the hypervolume analysis developed by Ben (Blonder) can detect “holes” in the functional space of communities, it seemed like the perfect moment to begin a research project focused on the study of such holes in hypervolumes. The idea that hypervolume holes could be a “Eltonian proxy” of vacant niches in communities quickly emerged from my first thoughts.

What are the key messages of your article?

Our study brings four key messages. The first is that vacant niches might be very common in plant communities. The second is that vacant niches can emerge from both abiotic (environmental filtering) and biotic (competition for resources) assembly processes. The third is that vacant niches are more likely to be found under harsh (cold) climates. The fourth key message is that vacant niches are invasible, which means that they represent viable ecological strategies in the community.

Does this article raise any new research questions?

There are three main questions raised by our article. First, are our results transferable to real world communities? Even if our simulation approach mimics observed forest dynamics, our results need to be confirmed with empirical data. Second, how general are the results? Here, we focused on temperate European forest, but we don’t know if we might obtain similar results in savannah, or tropical forest for example. The last research question raised by our article is: can vacant niches predict the invasibility of communities?

What is the broader impact of your paper (outside of your specific species/study system)

The broader impact of our paper is linked to the general debate on community saturation in ecology: our study supports the view that communities are not saturated with species. This idea is important because the fact that communities are unsaturated should push us to “reconsider” some ecological paradigms, such as the importance of competition in plant communities.

Who should read your paper (people that work in a particular field, policy makers, etc.)?

Insights brought by our paper may be of interest for a broad readership of community and functional ecologists. Our study addresses a broad and controversial topic, which is crucial in the debate on whether ecosystems can reach equilibrium or could theoretically become maximally saturated with species. Moreover, it could also be interesting for conservation biologists, as the existence of easily invasible vacant niches might provide some insight on invasive species ecology.  However, I think that our study is too “conceptual” and too far from empirical observations to be useful to policy makers or to be applied in the field. I hope that in the near future, we could work on similar questions using empirical data, and provide advances to better understand and predict alien species invasions in the light of vacant niches.  

Did you have any problems setting up the experiment/gathering your data?

Hiking in Grand Canyon with the Macrosystem Ecology Laboratory
Hiking in Grand Canyon with the Macrosystem Ecology Laboratory

The first main challenge was handling the model used to simulate forest community dynamics. The second main challenge was finalizing the development of the model to include individual trait variability (a condition sine qua none for our study), which took several months. It was finally overcome by Xavier Morin and the team working on the development of the model (including Francois de Coligny). The third main challenge was increasing conceptualization and efficiency when using the hypervolume analysis approach (our brain is not made to think in more than 3 dimensions  and running the analyses can take a lot of time!). Thus, I was quite surprised when I saw the shape of the regional hypervolume XD when projected in 3 dimensions! (see supplementary in the paper)

What is the next step in this field going to be?

One of the next steps would be to gather enough data across a broad range of environments to estimate the prevalence of vacant niches in different ecosystems. Personally, using empirical data of alien species invasions in grassland communities, I would like to compare the characteristics of the resident community’s functional hypervolumes with the invader’s traits. The idea is to test (1) if communities exhibiting hollow functional space are more susceptible to invasions from alien species, (2) whether invasion events fill the hypervolume holes of communities, and (3) if functional trait values of invasive species are consistent with the characteristics of invaded holes.

About the Author

How did you get involved in ecology?

As far back as I remember, I have always been sincerely attracted by the exploration and understanding of nature (the fact that I grew up in the middle of a forest might have helped). I was later trained as a conservation biologist with the aim to work in natural reserve management. But at some point I became increasingly interested in understanding rather than managing nature, so I switched to an academic research path in ecology.

What are you currently working on?

Right now, I am focused on the concept of functional rarity and distinctiveness, trying to identify the processes driving the variation of species’ functional distinctiveness in space and across scale (with an empirical approach this time).

What’s your current position?

Since February 2020, I have been working as a postdoctoral researcher at the LECA in Grenoble with Dr. Tamara Münkemüller and Dr. Wilfried Thuiller.

What project/article are you most proud of?

This one, of course! I’m kidding… that’s like asking parents which is their favorite child.

What is the best thing about being an ecologist?

Social time with the lab at ASU mountain (Tempe)
Social time with the lab at ASU mountain (Tempe)

Unravelling and understanding the hidden complexity behind something that has always been so close to us (Nature).

What is the worst thing about being an ecologist?

Working within a field with such a huge level of complexity that reaching a decent amount of predictability and understanding is almost impossible.

What do you do in your spare time?

I love outdoor sports, especially those that include riding stuff. I am bad at everything, but I do a lot of different activities including mountain biking, kitesurfing, snowboarding, mountaineering… It is crucial for my personal balance, so I tend to devote a lot of time to it outside of work.

One piece of advice for someone in your field…

Don’t forget that we do the most wonderful job in the world.