Nacho Villar: the challenges of experimentally resolving the functional roles of large tropical forest herbivores

Nacho Villar, a post-doc at the Netherlands Institute of ecology, remembers the good times he had at Brazil, the challenges of running an animal exclusion experiment in the Brazilian Atlantic forest and how persistence, hard work and a little of cachaza are the key for a successful research.

Nacho Villar in the Brazilian Atlantic Forest
Nacho Villar in the Brazilian Atlantic Forest

Frugivory underpins the nitrogen cycle. That’s what our latest work published at Functional Ecology shows. A game-changer for tropical forest ecology, this work highlights the importance of large frugivores (such as white-lipped peccaries and tapirs) and their resources on the dynamics of nutrient cycling in tropical forests. However, I won’t elaborate further on our study or its implications, you can read a plain language summary here. If you never heard about a “fruiting lawn”, you should read it. Or you can email me if you please. For now, I prefer to concentrate on sharing some of the many challenges behind setting up and running our long-term experiment, including some of a personal nature. I believe this might be quite instructive and would help to permeate how hard it is to do the experimental work we do in the critically endangered and mostly defaunated Atlantic Forest, and how difficult it is to replicate and work with experimental designs tailored to other ecosystems.

Working with large mammals on tropical forests is not easy. At all. And carrying a long-term replicated multisite experimental exclusion experiment in the Atlantic Forest of Brazil requires high doses of blind commitment to it. To endeavour such work in the Brazilian jungle, you need a dedicated team, a long-term ambitious vision, a lot of patience, and a bag full of resilience and perseverance to deal with the unexpected day in and day out. The kind of qualities found at LaBIc Conservation Biology Laboratory at UNESP (Brazil). Mauro Galetti, lab leader and a genuine naturalist (now at University of Miami), has dedicated his entire career to the ecology and conservation of the Atlantic Forest. In the early 2000’s he realised that to fully understand the consequences of defaunation in tropical forests, exclusion experiments were badly needed, so he started to mastermind the largest exclusion experiment in the Neotropics.

So what is this experiment I am talking about? Well, the experiment runs 43 exclusion-open control pair plots (86 in total) through a gradient of defaunation on 4 different sites across the Brazilian Atlantic Forest, a major biodiversity hotspot. I am pretty sure all of you have heard in the media about the current rates of deforestation and fire outbreaks in the Amazon, but I am also quite sure few of you know much about the Atlantic Forest. Well, only 12% of the original Atlantic Forest is left, mostly in small fragments. Illegal hunting and harvesting is widespread. To put it graphically, this fascinating ecosystem it’s at the Intensive Care Unit.

Despite the areas where we work are not utterly remote, setting the experiment up was not easy task. For starters, before setting up the experiment, previous team members walked thousands of kms and conducted various preliminary studies so as to identify sites with large vertebrate communities of interest. This involved several graduate, master and PhD projects. I have heard many extracurricular stories from this early work, including attacks by lethal Africanized bees and tense negotiations with heavily armoured illegal hunters on the field. Not for the faint hearted.

White lipped peccaries

Once the sites and experimental design was decided, then came the logistical challenge of building the plots. Sergio Nazareth, our fantastic super-field technician, managed to hire hardcore local workers willingly to carry by hand up all the tons of wood, wire mesh and all other necessary material uphill to the location of each plot. I can reassure that a lot of cachaça was involved. I recall one of the workers badly damaged his back, and was hospitalized and went through surgery to recover. The rest just slept for weeks after the work. But I am also quite sure Sergio didn’t: most likely he woke up next day, cooked breakfast for everybody, and drove many hundred kms ready for his new assignment. But he had left his legacy: by 2010, the largest exclusion experiment in the whole of the Neotropics was ready to walk on its own.

For many of the years to follow Sergio and Valesca Zipparro, our expert botanist, were in charge of learning and identifying every one of the >7000 seedlings in our experiment every 6 months while the rest of the crew sat and waited, or, more precisely, focused on other projects. In the meanwhile, the forest took some revenge, and swallowed some 17 paired plots, so that 43 remain to the present day. That’s almost 30 % of the plots (and data) lost in less than 10 years. Not an easy plate to swallow.

Setting up the exclusion experiment

And there is when I enter the equation. In 2015 I flew from Aberdeen (Scotland) to Brazil and parked in the drawer my experience as population ecologist, and moved to investigate the functional role of large tropical forests herbivores and their impact on ecosystem functions alongside Mauro, Sérgio, Valesca, and the rest of the crew. In the subsequent years, I have come across many of the joys of conducting research in the jungle: I have run dozens of hardcore field campaigns and tasted the treats of getting lost in the forest, of sleeping on mosquito hell for countless occasions, of being flooded and sick and tired to exhaustion, so many times. I saw many weeks of planning flushed down the loo due to contingencies in the field. Hard-knitted student projects frequently failed, and then were reinvented or relocated to succeed. So, when conducting experimental work in the jungle, be ready to take failure as a regular sleeping mate. The level of bureaucracy involved is also substantial, to say the least.

And that is just a part of the job. Anybody who has worked with datasets of tropical forest communities, with intractable high levels of diversity where a bunch of dominant species coexist with hundreds of rare ones, knows that there is a very limited amount of generalities about the mechanisms operating that can be unequivocally inferred from the analyses of these. For example, it’s very difficult to do population level analyses for 99% of the plant species present, and equally difficult to find information on seedling traits of these.

Animal exclusion plot

Another critical burden is that the amount of trophic and non-trophic interactions involving large vertebrates that can be directly observed on tropical forests is also very limited. I can’t help feeling jealous when I read studies reporting behavioural observations of large wildlife in savannahs. On the Atlantic Forests, this is simply impossible. You can make hundreds of kilometres on foot without spotting a tapir or a band of white-lipped-peccaries. They might be there, but you can’t see them, partly because they’re elusive, partly because they are not within spotting distance, and partly because densities are thought to be much lower (I say thought because actually methods for estimating densities of most vertebrates in tropical forests are still utterly inaccurate). You can’t follow them and observe them from the distance with your “binos” sat on a Land-Rover. This is why we have been working with camera traps lately so as to explore alternative hypotheses and study coexistence between large vertebrates (Akkawi, Villar, Mendes, & Galetti, 2020), yet there is a very limited amount of information that you can extract from those, nothing compared to e.g. direct observations on grassland or more canopy-open systems. We have also used telemetry and radio-collars attached to white-lipped peccaries to track their movements and use of the plots, but again this technology is designed for more open ecosystem types, where collars just don’t break or stop working after a few weeks. That is, assuming that the animals are not illegally hunted before, which happens quite frequently on some sites.

In the context of the article published in Functional Ecology, the hardest part was to organise and improvise a lab to extract nitrogen within few hours from collection. We were hours away from any civilized prospect of extracting nitrogen using sophisticated methods, so we had to do it “in-situ” using alternative methods. But together with Claudia Paz and Leticia Bulascoschi, co-authors of the study, and the help of Carla, Natalia and Fulbert (graduate students), we managed to do it successfully without further traumatic consequences.

Luckily all that sweat is starting to yield its results. All the effort cast by generations of LaBIc students, core project staff Valesca and Sergio, all those relentless and frustrating fieldwork campaigns, all those marathonian evenings examining the patterns behind the datasets, all those glasses of cachaça, and the many thousands of hours staring at the forest and wondering “how does this really work?”, are starting to pay-off. Last year we published our first work with the long-term dataset where we showed that large frugivores regulate recruitment and (spatial) beta diversity of seedling communities  (Villar et al., 2020). This year, our new study on nitrogen cycling published on Functional Ecology is set to establish a new fresh view of how tropical forests work. It sets strong departures from classical hypotheses such as the elegant Janzen-Connell model or the famous Neutral Theory of Ecology and Evolution, and poses large tropical frugivores as key players in global carbon and nutrient cycling dynamics. And there is more exciting research from the experiment on its way, being cooked churrasco style.

Brazilian Atlantic forest
Brazilian Atlantic forest

The majestic diversity of tropical forests has inspired some of the most fundamental paradigms in ecology. Yet, the inner mechanistic workings of tropical forests remain poorly understood. Our novel work in the Atlantic Forest truly embraces a combination of naturalism and the experimental method, and a stubborn sense of purpose. It’s ironic that in the era of big data, macroecological studies and sophisticated technologies, naturalism still has a role in inspiring ground-breaking fundamental discoveries. Ecology is still a young discipline, and there are so many lost paradigms out there ready to be found. We have to be open, and embrace constructively the wisdom hidden under the superficial canopy of still poorly understood ecosystems such as tropical forests. Be ready tough, for a rumble in the jungle.

Read the article in full here

Villar, N, Paz, C., Zipparro, V., Nazareth, S., Bulascoschi, L.; Bakker, E., Galetti, M. (2020). Frugivory underpins the nitrogen cycle. Functional Ecology,


Frugivory regulates the nitrogen cycle in tropical forests


Akkawi, P., Villar, N., Mendes, C. P., & Galetti, M. (2020). Dominance hierarchy on palm resource partitioning among Neotropical frugivorous mammals. Journal of Mammalogy, 101(3), 697–709. doi: 10.1093/jmammal/gyaa052

Villar, N., Siqueira, T., Zipparro, V., Farah, F., Schmaedecke, G., Hortenci, L., … Galetti, M. (2020). The cryptic regulation of diversity by functionally complementary large tropical forest herbivores. Journal of Ecology, 108(1), 279–290. doi: 10.1111/1365-2745.13257

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