The ComPOSTer: Interview with Professor Daniel Rubenstein

Professor Daniel Rubenstein is the Class of 1877 Professor of Zoology in the Department of Ecology and Evolutionary Biology. Last month, I interviewed him about the intersections between food, agriculture, and the environment and how these topics related to environmental justice.

Professor Daniel Rubenstein
Photo Source: Department of Ecology and Evolutionary Biology

Interview edited for length and clarity

Q: Why are you interested in food, agriculture, and the environment?

A: I’m a behavior ecologist and what that means is you look at how the environment shapes animal behavior. So you’re looking at how changes in environmental factors, ecology, climate, etc. affect different species and in different environmental contexts. I’m interested in unraveling those patterns and I use a lot of modeling and comparative analysis to try to find general rules.

The species that I have studied most extensively are the equid, or the horses, zebras, and the wild asses. They’re all very closely related evolutionarily because they’re all the same genus. There are very few species left on the planet (only seven) and are not particularly numerically abundant anymore anywhere but they’re widely distributed.

Now, when they cover the planet, everyone who is a farmer who has livestock cattle, sheep, and goats believes that every grass blade in the environment belongs in the belly of their livestock and when they see horses, zebras, or wild asses eating the vegetation, they are very unhappy. And they want them gone and so they persecute them and cause the extinction of these equids. Since I study them and people consider them vermin, I got involved in farming. I needed to talk with the pastoral people and the commercial ranchers who didn’t like the animals that I studied. In order to find out why they persecuted them, I started doing experiments to demonstrate that in fact there’s not so much competition between them. It’s actually mutualism because the equids can eat the stems in the straw that the cattle find difficult to eat and therefore they open up the grasslands, take away the negative foods, stimulate the growth of the good, highly nutritious foods as long as there’s moisture in the soil and therefore benefit the cattle. And so the “vermin”, all of a sudden now are facilitating the growth of the cattle and the cattle — by feeding with their tongue — are stripping away the larvae that parasitize the guts of the equids and so as a consequence, there’s a joint mutualism using different currencies.

And so this experience made me interested in farming and I teach a course on agriculture, human diets, and the environment, precisely to talk about these issues and other issues like where did farming come from? Why did it supplant hunter-gathering (which was a perfectly good lifestyle)? How do you deal with the fact that you have no nitrogen in your soils or water? What are the resulting impacts on biodiversity? I set up the course so that the students would need to play with and analyze farming data to really sink their teeth into what evidence exists that explains how different types of farming have different impacts on the landscape, lead to different productivities, profits, and also to different distributions. Who can afford organic foods? If you’re poor, you can’t. And so now you have a social equity issue as well playing into it. 

Q: How does the S.C.R.A.P. Lab relate to your course?

We received a grant from the university to examine different farming practices on several farms around Princeton. In the summer, we put out sensors in the field to measure metrics like evapotranspiration which is a measure of plant metabolism via water intake. If the water is going up through the plants it means the plants are photosynthesizing so via evapotranspiration you know how hard the plants are working effectively in terms of productivity. The students in the class pick different projects so they can compare commercial industrialized farming with organic farming,  biodynamic farming, or precision agriculture which puts the artificial fertilizer in places where plants appear are needed rather than blanketing the landscape. 

On Princeton University-owned farmland, we’re also interested in top-down pressures of herbivores eating the maize or soybean since the farmers leasing the land predicted that 30% of their crops were disappearing due to deer. So we sent out experiments to test whether that in fact was true by fencing off some of the lands with an electric fence at the same time that we are assessing the bottom-up factors (e.g. soil fertility). And that’s where the composter comes in. We can apply artificial fertilizer, which is what the farmers currently do, or we can have the soil additions be the compost. Each of these has different effects on the outgassing of CO2 as well as energy inputs. It turned out that the main cause of the loss of food was the herbivores or the deer but the nutrients do matter. We will be examining the effects further along with cover crops as well. 

Q: Why is it important that we study the intersections between these three fields at Princeton University?

A: I think it’s important for us to study it on campus because we all bring slightly different perspectives to the notion of how plant productivity in general operates. One of the things about food is that students love food. It becomes a touchstone, a magnet that brings people into understanding – well, what am I eating? Is it healthy? What impact is my diet having? Everyone has strong beliefs about this. Some say “I’m a meat-eater because humans evolved to be meat-eaters”. Others say “I’m going to stay as an omnivore”. And others say that the footprint is too great, therefore, I’m going to become vegetarian, in fact, I’m going to become vegan. And so people come in with these really strong beliefs. It turns out there’s no perfect way to eat. That each one of these diets has issues and difficulties in one way or the other.  When you do a life cycle analysis with all of the inputs, it turns out that what you think is the best type of farming often has hidden costs that you don’t appreciate. So there’s a lot of issues and my course brings out these issues to force people to rethink their beliefs. 

Others who are biogeochemists and genomicists can really look at biology or chemistry and bring in the understanding of different breeds, different genetics, and the relationship between the genetics of the plants vs the insects and pests. So when you can start to look at genomics, you can start thinking about ways in which you can build better plants that get into GMOs (Genetically Modified Organisms). Crop engineering has very low impacts on the environment, both in terms of maintaining biodiversity and in managing water and gas production, but brings up issues questioning if GMOs are healthy for you and others, so there are unintended consequences. And the more we can bring knowledge to dealing with these trade-offs and preconceived notions, we start to make better decision-makers by sharing the knowledge with students and colleagues.

Even if we can’t agree on the right answer, the more information we can give students, the more skills we can give them to think through these wicked problems which are not easy to solve. That’s why the introductory, environmental nexus course was created which was based on the four pillars of Climate, Food, Water, and Biodiversity. We had to make sure in the Environmental Studies program that there were upper-level courses to build upon the themes that were being introduced in the foundational courses. And so that’s how my course arose, and then there are other courses such as history and literature courses that deal with farming, diets, and self-worth. We’re trying to think about putting together a food certificate program that would bring these together going forward.

Q: How is the work that you are doing related to environmental justice?

A: The justice implications are very real. Organic produce is much more expensive. If I go to the supermarket, I can get an ear of sweet corn for 30 or 50 cents depending on whether it’s on sale. If I go to an organic farm or a farmers market, that same ear of corn is going to cost me 75 cents or even $1, and that’s much more expensive. If you’re limited on money and you want to eat natural foods you’re going to go buy food at the grocery store and not at the organic farm. And there may be pesticides on that food. Are you washing it carefully enough? If not, then you’re ingesting chemicals that will impact your health. The organic farmer would have grown it without chemicals or a different set of chemicals that are deemed to be safer for you than the ones they use in industrial agriculture. So right away, the limits in your income and the ability to get out to a community-sponsored agriculture location are very, very different.

When I conduct different livestock rearing experiments in Kenya’s 55,000-acre, Mpala Conservancy, we open them to the pastoral herds in the community and hire the children as the herders. They’ll live at Mpala, earn some cash, and in doing this new type of herding they are seeing the difference in the growth and health of their cattle. I can publish a paper on it and do a community presentation, but the telegraph from child to father is much faster and much more effective. By participating, you take ownership of the experience and you can spread it much faster because you become an ambassador. 

At Princeton, we hope to create a farm and invite kids from Trenton and Ewing, who may not have really healthy diets and engage them in actually growing and tasting vegetables. In doing so, they may experience something novel, and probably compel them to switch their diets. But most importantly, we will give them the crops to take back and sell within their communities. And that’s our belief that if we bring kids from urban centers and bring them into farming, not that they’re going to be farmers in the future, but they will start to appreciate and become aware that diet is something they can choose if they have access.