Mark Davis is the DeWitt Wallace Professor and Chair of Biology at Macalester College, Saint Paul, MN, where he has taught since 1981. His teaching and research interests include both plant and animal ecology. For more than twenty years, Mark has conducted research at the Cedar Creek Long Term Ecological Research site in east-central Minnesota, where his invasion research has focused on the invasibility of grasslands. In particular, he has studied how non-native grasses may influence the ability of woody plants to spread into grassland environments.
To date, Mark has written numerous articles and contributed chapters to various publications on the topic of invasion biology. More recently, he completed his own book, Invasion Biology (Oxford University Press, 2009). Deemed “a bombshell of a book,” by Scientific American, Invasion Biology has caused quite a stir among ecologists. In it, Mark discusses the history, philosophy and language that have defined and influenced the field of invasion biology. Highly critical of the dichotomous “native vs. alien” embraced by so many ecologists, he poses questions such as, “What if species were not labeled as native and non-native?…Instead, what if ecologists had taken a more quantitative than qualitative perspective, emphasizing a continuum rather than categories, and referring to the new species as ‘new species,’ or ‘recently arrived species,’ or ‘new residents’ to distinguish them from ‘longer term residents’? Might researchers have asked different questions?” He then proposes a variety of options for improving what he still believes to be a robust field. This past spring, Mark and others communicated a similar message to a broader audience, with the publication of an essay entitled “Don’t judge species on their origins” in the journal Nature (Davis et al 2011). While some may view him as a maverick, many of his ideas seem to be gaining support within and outside of the field.
We were thrilled to have a chance to chat with Mark to learn more about how he views novel ecosystems, non-native species and the future of invasion biology.
You have been teaching biology for nearly three decades. How did you become interested in invasion biology?
I was a history of science major at Harvard, but I took lots of courses in humanities and in the social sciences. I got a Masters in education at Harvard, and my specialty was human development, so that also involved social science. A couple of years later, however, I felt that my strengths lay more with science, so I went to graduate school for biology at Dartmouth. I focused on ecology. Then I came to Macalester.
I’ve always been very self-conscious, as a scholar and a person; always thinking about what I’m saying, why I’m saying it, and why I’m thinking this way. When restoration ecology really began to emerge in the 1990s as a distinct and popular field, it became very obvious to me that it was a very value-based field. There were assumptions being made about what the target ecosystems should be, and they were so obviously culturally-based. For example, in Minnesota in the 1990s, if you were restoring habitat, that meant you were restoring it to the way it was in the mid-1800s, which is when Europeans arrived to settle the area.
An explicit part of restoration ecology in the 1990s-and actually into the 2000s-meant getting rid of non-native species and restoring native species. There were a number of people who saw this arbitrary, non-scientific, ideological dimension to restoration ecology, but most ecologists never did. It just really started to bother me. I remember going to a restoration ecology meeting in the early 2000s and, to be perfectly honest, I was embarrassed by what I was hearing. People were presenting ideas as if they were scientific, when they were clearly culturally value-based opinions, perspectives and frameworks. The speakers didn’t seem to recognize or acknowledge that. In my mind, this is very bad science-when practitioners are not conscious of the social context influencing the frameworks, policy decisions, management goals and objectives they present
At this time, I was doing ecological research at the Cedar Creek Long Term Ecological Research site, about 30 miles north of the Twin Cities. My work there was straight data-collecting field experiments. Some of it did involve non-native grasses, but my critique of invasion biology was independent of this research. It really arose from my own observations of what was going on, which I felt was bad science and bad for the field. I was not alone. There were not a lot of us, but there were a number of people who were making the same observations and conclusions. A number of them were outside the field of science. There were some philosophers and sociologists who recognized immediately this kind of cultural value bias that most scientists seemed not to acknowledge or even recognize was happening.
Who were some of these other people?
They included philosopher Mark Sagoff, landscape architect Paul Gobster, historian of science Matt Chew and sociologist Brendon Larson.
The problem is that disciplines are rarely open to criticism coming from outside the field. (I don’t view this as a shortcoming of just ecology. It is common throughout academia.) So people like Sagoff and others were dismissed as not knowing what they were talking about because they were ‘outside of the group.’ But I couldn’t be dismissed that way because I was part of the group.
For readers who may be unfamiliar with the history of the field of invasion biology, can you summarize the field’s current status, and provide a brief history of how we got here (including how was it influenced by people like Charles Elton, and entities like the Scientific Committee on Problems of the Environment)?
Charles Elton wrote his famous book [The Ecology of Invasions by Animals and Plants] in 1958. In this book, he used lots of incendiary language and military terms [when describing] the movements of species (e.g., “explosions,” “invasions,” “invaders”). Interestingly, the field of ecology didn’t respond in any significant way for almost a quarter of a century. In the early 1980s, a group of ecologists began to become concerned about the continued and accelerated movement of species by people around the world. They organized a number of meetings, some of which were funded by the Scientific Committee on Problems of the Environment (SCOPE), and they really defined the field of invasion biology. They also determined [the field’s] key questions and gave it its vocabulary.
I doubt it was a conscious decision, but a choice was made to frame this phenomenon of species being moved around the world as “invasions” and to call species that were being moved from one place to another “invaders.” In the 1980s, the term “invader” meant any species that was moved and was not native, not just non-native species that were causing problems. The phenomenon did not have to be framed this way. It could have been framed as “species additions,” for example. Species were taken from some parts of the world and added to communities and ecosystems in other parts of the world. The phenomenon could also have been called “global mixing of species,” a more neutral characterization that does not embed the phenomenon into this highly value-based language. That language set the tone for decades. It was obvious that non-native species were not desired, as you don’t call something an “invader” unless you have a negative opinion about it. Most ecologists and most of the public embraced this notion that we were being “invaded.”
People love to hate an enemy. I think we are predisposed to think that way as a result of evolution. If we don’t have an enemy, I think humans will create one. The enemies we really don’t like are the newcomers. It was so easy to get people to view introduced species negatively. There is great value to a society in having a common enemy because it’s a bonding device. Dictators do this all the time. When things get bad in their country, they’ll start emphasizing that they are being threatened by an enemy abroad.
So invasion biology thrived, particularly in places like the U.S., Australia and New Zealand. This is ironic because these are countries where the vast majority of people living in them are relative newcomers themselves. (That’s a question for someone to answer: Why do so many people who are immigrants themselves hate this different kind of immigrant?) At that time, the field was very black and white. Natives were good. Non-natives were bad. For most managers and people working in the field, there wasn’t much distinction between “non-native” and “invasive species.” The terms were used interchangeably. Some people still use them interchangeably today. That’s one of the big problems.
There are thousands and thousands of species that have recently been introduced, but only a small portion of them have been deemed problematic by society. According to U.S.law [Executive Order 13112, Signed by President Clinton in 1999], the term “invasive species” is supposed to be reserved only for non-native species causing what society has deemed to be “harm”. The fact is that an awful lot of people-including professionals-don’t always make the distinction. They use the two terms interchangeably. Non-native species as a group are still generally lumped with species that are doing things we don’t want them to do.
Beginning around the year 2000, there began to be more frequent criticisms of the field [of invasion biology]. Again, much of this was coming from outside the field from Sagoff, sociologists, and another historian of science, Matthew Chew. The criticism became more common, but we were still a small group. Either we were ignored, or, if we did publish something, immediately in the next issue would be a rebuttal. Frankly, that’s still going on. It’s a slow process. In this country, it’s probably going to take a generation to get away from this ideological perspective that whether a species is desirable or not depends on how long it has been here.
This is a highly emotional topic, which itself is interesting. Why would people who are being criticized for their general dislike of non-native species become so defensive and emotional? To me, that means that there is a much bigger, underlying narrative that is being threatened. It’s difficult for people to change very fundamental beliefs. For some, it has a religious-like aspect to it. It does make things very clear: there are good species and bad species. Humans like things to be clear.
To what extent do you think the field of invasion biology has been influenced by nostalgia and by human tendencies to categorize the world around them?
They play a huge part. We are predisposed to think in particular ways. Our human brain has evolved to characterize the world. I don’t think anyone who has studied the brain or human behavior would question that. Moreover, most of the people who study this believe that we are not only predisposed to categorize the world, but we are predisposed to do so in a dichotomous way: us vs. them; in vs. out; good vs. bad; immigrant vs. citizen. Anthropologists say that all cultures tend to have these dichotomies, particularly “us vs. them.” I think because we are all mortal and our identity and meaning for life is often rooted in the past, humans aren’t very good at adapting to change. The world we knew, which was important to us, seems to be getting lost or replaced, and that’s a difficult thing for humans to reconcile.
Can you elaborate on the “underlying narrative” about being threatened that you mentioned a moment ago?
I think this is all part of a defensive human reaction against the very rapid globalization that Earth and all humans are experiencing right now. That includes cultural, political, and biological globalization. Things have changed extremely fast over the past generation or so. The world that those of us who are 40 and older knew growing up doesn’t exist anymore-culturally or biologically.
Cultural historians have observed that when things change too rapidly, a very common response is to try to slow things down. There is a feeling that things are getting worse and that the desirable days of the past are being defiled by new ideas, new people, new species. There is a rising sense of insecurity about the future. When things are changing very rapidly, there are often very strong efforts by groups of people to reverse that, to try to push back the new stuff in order to re-establish the beliefs, cultures, or ecosystems of the past. That’s fundamentalism. Whether it is religious fundamentalism or ecological fundamentalism, the desire to make things like they were in the past and view agents of change as villains who are somehow polluting what had been so pure in the past, is a fundamentalist view.
What do we know about the amount of resources devoted to battling “invasive species,” both here in the U.S. and worldwide?
It is clearly billions and billions of dollars. At the same time, there is no question that some of these species together are causing billions and billions of dollars of harm. The issue is this: to what extent is the money we are spending being directed where there really is harm being produced?
It’s the same for native species, though. Every year, billions of dollars are spent trying to control native species.
Why put these species into two groups? We have species that are causing what society deems as problems, and we spend society’s resources to try to make them less of a problem. Some of those species are native and some are non-native.
Rather than continuing to allow the “native vs. non-native” dichotomy to guide conservation and restoration management, you urge people to prioritize efforts based on the “level of harm” a non-native species poses-to biodiversity, human health, ecological services and ecology. So how do you define harm?
Harm is in the eye of the beholder. One of my criticisms of the field is that society was never really given the opportunity to decide what was harmful or not. The scientists told society which species were good and which were bad. When scientists communicated to the public and policy makers about this issue of species being moved around, they didn’t just come with the information, they came with a value-based agenda already decided. Non-scientists played a minimal role in deciding what, from society’s perspective, was harmful. That’s something that needs to change. It’s not just an issue in invasion biology. I think the same is true in climate science. By no means should scientific findings and discovery be put up for public vote; however, whether these findings or changes should be considered harmful or worth spending money on preventing…that is not something scientists should do by themselves. Those decisions need to be made in a collaborative way with the general citizens.
By “citizens,” you obviously mean humans. You say that harm is in the eye of the beholder, but how would your respond to someone who might ask, “Why do humans get to be the beholders? By letting novel ecosystems flourish, you are no longer protecting the rights of all species.”
First of all, there’s no way anyone can take a non-anthropocentric view. We’re humans, we’re thinking, and we’re the ones making the decisions. Even if you’re saying you’re doing something for another species, that’s still an anthropogenic perspective. Nature doesn’t care. Nature’s just out there. Any management is going to be an anthropogenically-based activity, even the decision not to manage.
Valuing diversity is a human, anthropogenic perspective. Nature doesn’t care if it’s diverse or not. Personally, I love diversity. It’s what I teach in my classes, and what I enjoy in my spare time by bird watching and looking at spring flowers. But I don’t have this big distinction between whether a species has been here 50 years or over a thousand years.
I have never said that we should not do anything. That is completely not what any of us was saying in our Nature essay (Davis et al 2011). In fact, we were as explicit as possible that we were not saying: “Yeah, just throw up your hands, let all species go wherever they want.” Not at all. There is no question that there are many introduced species causing threats to human health, and there are species causing great economic damage to societies. There are also native pathogens that can kill people, and there are native species causing billions of dollars of economic harm.
If we were to take a vote, I think there’d be little disagreement about whether or not human pathogens are harmful. What about this insect that kills hundreds of millions of ash trees? Is that a harmful species or not? I don’t think there’d be much disagreement that this is a harmful species and we should try to do something to mitigate the damage and reduce the effect. But let’s say you have species coming in, and a native species might be becoming less abundant. Is that harm or is that change? Again, that’s what society has to decide. Invasion biologists have typically presented the decline in the abundance of native species as harm. I don’t buy it. If you’re working on your own land and using private money, do whatever you like. But if you’re using public resources and public monies? Boy, I find it very difficult to [favor] trying to reduce the abundance of species that have come in when their only effect might be changing the relative abundance of other species (not driving them to extinction).
It’s all in your point of view. Here inMinnesotain the 90s, [descendants of] Europeans were running the DNR. The Twin Cities area now has big Somali and Hmong populations. What if the Somalis or Hmong were in charge? Species that Europeans think shouldn’t be here were here when these other groups arrived. The argument has often been that we need to get rid of non-native species so we can develop a better sense of place? Well, not to the people who arrived here recently. Those species are part of their sense of place!
Do you think that many who oppose the idea of novel ecosystems are simply not thinking in long enough time scales?
I don’t even think it’s a time scale phenomenon, because these novel ecosystems are happening very fast. Novel ecosystems do not just consist of a new mixture of species. Novel ecosystems are usually getting double the nitrogen input they were 100 years ago. The climate is changing. Disturbance regimes are different. The new species coming in are just part of it.
If there were to be a novel ecosystem poster, what would be an ideal “poster species?” Can you tell us about one species that you feel has really been falsely vilified in the native vs. non-native paradigm?
It really varies from place to place. Here in theMidwest, you could think of garlic mustard and purple loosestrife. They have been vilified as out-competing the native plants and driving them to extinction. In the 1990s inMinnesota, a great deal of money was spent on eradicating purple loosestrife. Most of that was based on a very basic misunderstanding, particularly with garlic mustard, which is a wildflower in the forest. Scientists saw two things happening at the same time. They saw native species declining in abundance and they saw some species like garlic mustard increasing in abundance. It’s a fundamental, junior high school level mistake of assuming cause and effect. Studies that have since been done (not only on garlic mustard and purple loosestrife) have found that in many cases, these new species had very little and sometimes nothing to do with the decline of the native species. The environment was changing in various ways that was not to the benefit of the native species and that’s why they were declining, and the non-native plant species were adapting to this changing environment so they moved in. So here, garlic mustard would be a classic.
What was the reaction to your article, “Don’t judge species on their origins,” which appeared in the journal Nature this summer? How did that reaction differ from reactions to your book Invasion Biology?
Invasion Biology was written for a peer audience. All of the reviews I saw were very favorable. Obviously there were certain people who didn’t like the message that was coming out. [Reaction to] the essay was just what I expected. I received emails from colleagues that were very supportive. Some saying, “I wish you would’ve contacted me. I would’ve loved to have been associated with the essay.”
I got a number of emails from general citizens saying, “Thank you, thank you, thank you for bringing some common sense and rationality to this non-native species issue.” Some citizens been really upset with the dominance of this nativism paradigm. When a group wants to characterize something as the enemy, they can vilify it to such an extent people are willing to do almost anything to get rid of it, including spraying chemicals into the environment. A lot of citizens have been very upset with eradication programs, which in their view are doing much more harm than the claimed harm of the species. Because the native/non-native perspective has been so dominant, they’ve always felt they’ve been the minority voice. So I have received a lot of positive feedback from peers and the general public.
On the other side, I got an email or two from peers that were almost threatening. It’s not surprising, really. The fact is that people, organizations, and companies have a lot invested in the native vs. non-native characterization of nature. For the scientists, this is how their careers have been defined. They’re invasion biologists. There are companies out there for whom a big part of their business is spraying to get rid of non-native plants. Some conservation groups have raised lots of money by communicating to their followers what a threat these non-native species are. It’s not exactly at the level of the military industrial complex, but there is a lot of momentum out there that isn’t going to be stopped easily.
Science writer Emma Marris says there are two questions she is always asked by those who oppose her point of view about nature. One is, “How can you say invasive species are not bad?” The other is, “Although baselines may be arbitrary, and some non-native species may be useful, if you say that out loud, aren’t you giving ammunition to the forces of evil?” Did you get any of that kind of reaction?
Oh absolutely. I’ve been getting that for years. When I criticize the hyperbole, the militaristic language, the black and whiteness, the non-recognition that so many of these non-native species are either benign or doing good things, the most common argument is, “We can’t say that! That’s going to give ammunition to the other side!” Getting that reaction very much depresses me.
Frankly, I think this is a big problem within the various sciences that deal with the environment. Some scientists seem to be more interested in communicating a particular message than in communicating the whole story. There are efforts to manipulate and massage the message to the public and to policy members. That can get you short term gain, but it almost always backfires in the long run. At some point, the word is going to get out that the scientists have not been telling the whole story. Then, you are threatened with losing your whole legitimacy, which can take decades to regain.
I’ve always felt that the best approach is to tell the whole story to the public. Massaging the message shouldn’t be the role of the scientist. The scientist should collaborate with the public to decide what these findings mean. The public does not like to be told from the experts on high what to value and what not to value.
Do you feel like you heeded your own advice regarding communication when you and your colleagues wrote the essay in Nature?
We did. I’m always very careful to emphasize that there are absolutely some non-native species that are causing great harm, but that’s just part of the story. The whole story includes also communicating that nonnatives are just species. Some we’re going to like; some we’re not going to like; some won’t be on our radar.
You discussed the role of the scientist in communication. What about scientists’ responsibilities regarding communication?
A scientists’ responsibility to the public is to communicate his or her findings. Then, the scientist has a responsibility to collaborate with citizens to determine what should be valued and what should be considered undesirable. Scientists should not tell the public what the social consequences of their findings are and what required social response should be. The public does not like being treated like children. I don’t think scientists in the environmental field have done a good job of bringing the broader community into the discussion of what these findings mean in terms of society’s values.
In your book, you encourage invasion biology researchers to think of their work in a broader conceptual context. Can you give an example of someone who has done this effectively? If so, has that translated to any community or entity adopting a “level of harm” vs. a “non-native=bad” approach in the management of non-native species or of natural resources in general?
I’d say we’re in a period of transition. There’s definitely part of the old guard that still holds strongly to this native vs. non-native [viewpoint], but they are now being contested by a growing number of people who think we need to take a much more pragmatic (and scientifically sound) approach where we’re not so preoccupied with where a species is from. There are also community groups who are becoming more organized and standing up to oppose traditional eradication efforts of non-native species. This is happening around the country. There are a number of citizen groups in California, for example, that are contesting eradication programs-the amount of chemicals used, or the number of trees cut down-in the name of restoring more native environments.
It’s like most things. There is a large group of people that will never be convinced; eventually their message will diminish over time as more and more of them die. This will not be an issue in 2050 because those people are not going to be with us anymore. The people alive and active in 2050 are now growing up in this globalized world. They’re not going to be threatened by rapid globalization. That’s the only world that they know!
What about more research of novel ecosystems? The authors of the article that appeared in Trends in Ecology & Evolution two summers ago Novel ecosystems: implications for conservation and restoration (Hobbs, Higgs & Harris, 2009) recommend: “More detailed ongoing examination of novel ecosystems, and how to recognize, quantify and manage them, is required to equip us to deal effectively with the new ecological world order.”
In early September, I went to a meeting/workshop in Switzerland dedicated to the topic of “Ecological Novelty.” A lot of ecologists are thinking very explicitly about this new perspective that needs to be taken. Richard Hobbs himself, who was actually one of the leaders in restoration ecology, told me he is getting flack from some of his colleagues because he has become more critical of the restoration perspective, advocating that we should possibly even drop the term [restoration]. Just as the choice to use the term “invasion” was unfortunate because it set the field on a particular track, so was choice to use the word “restoration,” because it immediately causes you to have the past define the goals.Hobbs is suggesting changing “restoration ecology” to “intervention ecology.” That is a neutral term. It doesn’t have an implicit agenda, as there is with the words restoration ecology and invasion biology. Values were being cloaked in pseudo-scientific terminology with the usage of those terms.
Emma Marris believes we should view nature as the living background to human lives. Would you agree?
I agree with Emma on just about everything. I guess I would say we need to view nature as constantly changing, and that there is no prescribed way that nature is supposed to be. There is no such thing as a healthy ecosystem or an unhealthy ecosystem. That’s another example of cloaking values in pseudo-scientific language. An ecosystem is just an ecosystem. It’s not an evolutionary entity. When someone refers to a “healthy ecosystem,” what they’re really saying is, “That’s the way I want the ecosystem to be.” That’s fine, but that’s how we should state it. We shouldn’t pretend that we’re doctors making ecosystems “healthy” again. Ecosystems don’t care what they are.
Nature doesn’t have a direction, function or purpose. Humans decide that. It’s up to us to decide what we want nature to be like.
What does the future look like for your field? What are you working on? What are your students excited about?
The field of invasion biology isn’t going to exist in several decades. A couple of months ago, when I was flying back from the Switzerland meeting, I was reading a newspaper and it was quoting an urban sociologist on his views of some of the findings of the 2010 census. Some were remarkable. For example, something like one in every seven committed relationships consists of people from different cultures or ethnic groups. Also, in the last 20 years, the number of Hispanic people that have moved into the country is equal to the current population ofVenezuela. [The urban sociologist] said that in 2050, people are going to look back and wonder what all this talk and concern was about diversity and immigration. That’s just going to be the world then. When you fill out forms, you’re not going to be asked to check your ethnic background because it’s going to be meaningless then because everything will be so mixed. It’s the same thing with respect to species. This native vs. non-native notion is not going to hold up. Our biota will be such a mixture of long term and recently arrived species, and for the people who grew up with this mixture, it’s going to seem ridiculous to continue to characterize some species as native and some as not.
I view the concept of invasion biology as a 20th century concept or enterprise, which is in the process of losing its meaning and will continue to do so in the coming decades.
Do you see growing acceptance of idea of novel ecosystems among your students?
Most of the students come in with the native/non-native idea. That’s been the dominant perspective they’ve grown up with in theUS, and they’ve drunk the Kool Aid. After spending a class or two with me, though, they recognize the cultural dimension to that perspective, and they begin to take a much less ideological view of species.