30 min read

The War on Invasive Species Is Making Things Worse: An Interview With Erick Lundgren

On feral ecologies, the failures of invasion biology, and the blurred lines between introduced and native species
The War on Invasive Species Is Making Things Worse: An Interview With Erick Lundgren

Saul here. Sometimes in science, there are things that everyone knows with such uncontroversial certainty that no one bothers to check.

At Heat Death, our house example for this is the long-held belief that Komodo dragons didn't have venom, but killed their prey with a bite from their mouths which were swimming with septicemia-inducing bacteria. But as leading nature journalists Ed Yong wrote in National Geographic, this was something people were so sure of that for decades no one actually bothered to test whether or not it was true. When they did, in 2013, scientists were very surprised to find that the dragons had venom glands which could pump out toxins powerful enough to kill a water buffalo.

With that in mind, let's turn to another idea that's so uncontroversial as to not seem to be worth arguing about: that invasive species are on the march throughout the world, spreading chaos to native ecosystems.

You’ve heard the stories: a vast and verminous rogues gallery, introduced or unshackled by human hands, pushing into ecosystems where they never were before — and where there are no predators to control them. Donkeys in Death Valley. Rats and goats on windswept Pacific islands. Asian carp in the Great Lakes and lion fish in the Gulf. Feral hogs across the U.S. Cats and rabbits and god knows what else in Australia.

The idea is that these animals are all, in their own way, fundamentally alien to their new homes. And in the name of conserving the environments into which these new migrants are pressing, wildlife conservation officials around the world argue, they therefore have to spend a lot of time destroying wildlife.

The result is essentially a long term counterinsurgency against the streams of animal migrations, as species jump aboard human transport or cross our infrastructure or simply walk away from climates and ecosystems we are helping to destabilize. And the tactics of that counterinsurgency — carried out by government employees and contractors — look rather similar to the ones once seen in Iraq and Afghanistan. Australian hunters bag and poison feral cats in the bush with high-powered rifles. Texas government officials proposed spreading poison across the whole landscape to kill hogs. National Park service officials in Death Valley, in liberal California, continually round up feral donkeys, who they say have no natural predators and trash the water holes for other species.

All of this happens, the thinking goes, because it must happen. Because there is no other way.

But what if there is? What if that whole model is bunk, and the difference between invasive and native species is far blurrier than we've been told? What if it's less about any scientific principle of wildlife or ecosystem management then a pseudo-religious desire to return us to Eden? And what if all the killing isn't helping ecosystems reach equilibrium, but instead pushing them ecosystems farther and farther away?

Welcome to Heat Death, the newsletter that seeks to broker a peace treaty between the so-called natives and the invasives. Our guest today, Dr. Erick Lundgren, is an ecologist with Sweden’s Aarhus University who specializes in unseen and feral ecologies. He’s also a wildlife biologist who’s spent his career pushing against the the idea that you can simply kill your way to a balanced ecosystem.

We're running this piece today in conjunction with Asher's new piece, out in the New York Times, which incorporates Lundgren’s research on how mountain lions are regulating one invasive species in a particularly delicate ecosystem, and how the full weight of the US government is preventing that balance from being established rather than encouraging it.

In a wide-ranging and fascinating interview with Asher, Lundgren talks about the importance of predators, why feral pigs get a bad rap, and why much of the received wisdom around invasive species is a mixture of prejudice, folklore and a circle jerk of mutually-supporting citations unsullied by any actual contact with evidence. The interview has been edited for clarity and flow.

This is Heat Death. Stay with us.

Turn And Face The Strange

Erick Lundgren, with cup.

The position that “native” vs “non-native” is a false choice isn’t that common a position in conservation work. What sparked your thinking on this?

After my undergraduate, I spent five years as a field biologist, field technician, doing seasonal jobs, with the USGS, with the Institute For Wildlife Studies, working on endangered birds. That was galvanizing as well, because we kept being in these situations where our knee-jerk action was just to kill things.

I was trying to be a biologist. I was asking questions like “what’s this plant’s relationship with these introduced organisms?” The responses from my bosses and from other biologists was always angry dismissal—this fervent religiosity that introduced organisms are fundamentally bad. And if I pressed them on that, with questions like “could you tell if this organism was introduced by its actual effects?” They would eventually freak out and say things like: You know what? Native species are just sacred. Or: Introduced species just don’t belong. Which are not scientific claims. Those are just value statements.

It just became increasingly clear to me that conservation was spending all of its resources in these landscapes, and many of these projects were just killing things—and we didn’t monitor to see if those killings led to any benefits.

Can you give me an example?

I was working in Maui, and we were mist-netting [putting up fine nets to catch and band birds -ed] for Maui parrotbills, this endangered bird. And if we caught a red-billed leiothrix, this beautiful frugivore from China, we were forced to cut its head off with scissors. This is one of the only frugivores in that forest! All the other frugivores in Hawaii are extinct.

Red-billed leiothrix, Arnie Kaiser

And just…what are we doing? Is cruelty to this organism that doesn’t belong somehow helping us care more about the parrotbill? It just seemed so blatant, this cultural disregard for non-human life. Like it’s all just machines. And if it’s all just machines, why the fuck do we care about the native parrotbill? Is conservation no more than antiquities collections? Are we protecting antique coasters? What’s the point, if they’re all just a bunch of automata that have no value as living beings?

There does seem to be this idea of redemptive violence in conservation. The idea that you can kind of kill your way to a better world.

It’s very odd. I think in some ways, it’s a type of bloodletting because we feel so helpless in actually helping the Earth. It’s kind of cathartic in the face of policy that we can’t change, global forces that we can’t change. I think a lot of the energy behind killing comes from — as my PhD advisor put it — us externalizing our own guilt onto other animals.

But that’s very common in conservation! And I think it has really problematic consequences, because it reinforces human exceptionalism, which many would argue is the very reason we have such a deleterious relationship with the planet. It turns a lot of people off of conservation. I’ve met random people that are carpenters now, and I tell them what I do, and they’re like: Oh, I was working in conservation, but I just fucking couldn’t stand killing things anymore.

It’s also funneling money and energy into something that we really don’t have any evidence is  effective. If you eradicate rats from an island, yes, there might be some benefits for the seabirds. But there’s almost always a lot of inadvertent consequences which require further management, not to mention being deeply, deeply disrespectful to non-human life.

What are the ripple effects of those kinds of elimination policies?  

It’s actually really interesting. Rats on an island are embedded in a network of relationships to survive there. If they're eating seabirds, that's seasonal, when the seabirds come to breed. The rest of the year, they're eating other things.

In one case, rats were eradicated and then an introduced species of ant—that was super rare on the island—somehow exploded in abundance. Exactly how the rat was influencing the ant, nobody knows. It could be like, three ecological steps away. But the ants then started eating the seabirds at the same predation rate as the rats. So then you have to put pesticide over the whole island.

They removed the cats from Macquarie Island in the Indian Ocean — it’s an Australian managed island — and it led to rabbit populations exploding and completely denuding the place. They finally removed the rabbits, but then the jaegers, a native seabird, began predating on the chicks of other seabirds, leading to like a similar mortality rate as with the cats, and the rats, and rabbits. So what’s the appreciable benefit? You’ve just created a bunch of piles of dead bodies.

Meanwhile, we know that overfishing is another major stressor on seabird populations, and also a stressor on coral reefs, on fish themselves, on sharks. So maybe we could take responsibility for our own actions and focus on overfishing as opposed to just killing things on islands.

You’ve also focused a lot on lingering holes in modern ecosystems left by Pleistocene extinctions.

I got to go to Tanzania for study abroad through the college. That was really formative, seeing what African ecosystems are like.

How so?

Well, the Pleistocene never really ended in Africa. These big animals are still around. Growing up in upstate New York, like many people in the developed world, or anywhere outside Africa, you have an animal community where your biggest animal is one deer species. If you're lucky, you might have three.

Go to Africa, and there's 11 antelope species, and then elephants, hippos, rhinos, and giraffes. There’s this gigantic cacophony of big animals. I had learned in high school that all the continents of the world had once been like that, and the reason that’s often given is that humans left Africa and over hunted them. But most of those big animals survived in Africa, which is very interesting. And so you can think of Africa as a sort of  window into how the Earth looked for 35-40 million years.

And it's very different than the quiet, pristine nature that we have in North America where these big animals are thought of as elusive ghosts. In Africa, big animals are powerful forces. Like lightning on the landscape.

It’s the difference between a deer scraping a tree and an elephant knocking one over.

Exactly. Just a totally different scale of relationship.

The North American conservation that I had been raised into, is very plant focused: the idea that a healthy ecosystem is an undisturbed plant community. But you go to Africa, and that's completely out the window. People, of course, value and are interested in the plants, but the animals are clearly this huge elemental force, like rain. A huge driving influence on the landscape. And they cause things that we consider ugly and unhealthy in North America.

Like what?

Places in North America that we would call disturbed, overgrazed or ruined. You see landscapes that look similar to that in the most wild national parks in Africa. In the Serengeti, you'll see waterholes that are completely trampled barren — something that in North America would lead to a call to arms. Which I’m sympathetic to, especially when it's done by unregulated livestock grazing.

Seems like the difference there is that livestock generally doesn’t range widely around on the landscape. You spent some time in Australia as part of your graduate work, right? How did that compare?

I didn't spend as much time in Australia as I'd have liked to! I wanted to do fieldwork there. Despite having such a small population size, the human impacts on that continent are really profound. [Laughs.] It's really hard to find a system that isn't an intensively grazed livestock system. There's actually very few, and almost the entire continent has poisoned baiting for dingoes. You have a population smaller than the population of California, that has nearly converted Australia to what we've converted North America to. Not intensive irrigation, but you could drive out into the Outback, and it's just millions of cows, and poison. It’s pretty depressing. [Laughs.]

Saul and I have sort of talked a lot about this concept of “Cattle-land” as discrete ecological unit. “Cattle-land” being a specific kind of environment that’s completely dominated by largely sedentary cattle herds, with ripple effects on plant communities.

Plus the other associated aspects of that. The supplemental water, fencing, the predator control. It’s a very different ecosystem than an ecosystem with feral cattle. I don't think it's a species identity that matters as much as the way we're managing them.

And also that these cattle are in female-only herds, it really changes the dynamic of what a wild feral cattle population would do.

How so?

My advisor in Australia spent a lot of time in the Simpson Desert, this very wild place—very hard to get to, no domestic livestock. But it has feral camels, feral cattle, and it has protected dingoes. And the feral cattle she describes as one of the most wild things she's ever seen, including in Africa and Yellowstone.


You don’t see the cattle. They're like ghosts. And then at dusk, they come to the water. And because the population structure is pretty much evenly mixed sex, it’s this extremely tense and violent affair. There are bulls with huge horns that are stampeding and charging each other and then bellowing, and the females come in and get a drink of water in their small herds and then they get the hell out and go back to the desert. It’s a totally different dynamic. It's not the 30 females sitting at the waterhole all day long until someone moves them.

Right. In these domestic systems, there’s absolutely no reason not to hang out by the waterhole all day.

And they don't necessarily know any better because they're not allowed to build a culture on the landscape. So responsible cattle management is the cowboys have to come and push the cattle to a different waterhole. And then at the end of the season, they put them on a truck and ship them somewhere else. So to say that domestic cattle are equivalent to feral cattle makes no sense.

For so long, ecologists have essentialized the impacts of organisms, as if they're essential to the species’ identity. But those impacts actually emerge in relationship to context, predation, and in the case of cattle, the tensions of a sexually dynamic society. Those things push organisms around. And it has nothing to do really with their essential traits, which, of course, are controlling what they can eat, and how they move, and all that other stuff. But the actual effect on ecosystems is much more complex and contextual.

You ended up carrying those questions into your fieldwork in the desert southwest, which turned into a long study on feral donkeys, or burros. What about them interested you?

I was working in the Bill Williams River in Arizona, one of my first field jobs in 2010. I was there looking at plants, and there were wild burros all over the place. These animals are like strange desert ghosts. It felt like being in Africa again at night, really wild and dynamic; coyotes howling, these donkeys screaming at each other. You come across them in the desert and they just stand in these small groups and watch you with these dark eyes. They're very enigmatic. But I was working with biologists that were like “Man, I wish you could shoot these guys.”

On a similar trip to that region, I started finding these wells dug by the wild burros to get at groundwater. So that was kind of this burning question for me: What are burro wells doing to water availability?

Tell me about the burro research.

Well, they intrigued me in part because I’d read Paul S. Martin's work about the Late Pleistocene (129,000—11,700 years ago). He noted that equids, the broad family of horses and their relatives, like donkeys, had been in North America for something like 40 million years. During the Late Pleistocene, we had desert-dwelling, ass-like horses and equids in the southwest. There were three to five species of equid across North America, maybe even more. So that’s a really interesting scientific handle—What are these reintroduced equids doing? He suggested that they might be recreating Pleistocene food webs.

Feral donkeys and horses digging wells in dry streambeds. Public domain, Erick Lundgren

You and your colleagues had a paper that came out last year showing the equid wells served as potentially important oases and germination nurseries for native species of desert plants and animals. What was the response?

That got contentious. Some people argued that the cumulative effects of wild donkeys are negative, therefore any digging — I think they called it a few holes — is irrelevant. The claims were that wild burros and horses out-compete native species, drive native species away from water, and then graze and disturb the landscape. So they feel that any claim that these animals are helping native species by increasing water availability is meaningless.

But wild burros are the subject of so many pseudo-scientific claims by federal agencies, state agencies, and by scientists.

What kinds of claims?

Some people have also claimed that because burros have incisors, that plants they graze on just automatically die. [Laughs.] That the damage just causes system-wide shutdown of plants, which is just insane. These plant species emerged about 2 million years ago in the fossil record. And until a blink of an eye ago, geologically, they were being eaten by equids.

A big one is the idea that feral animals reproduce more rapidly than native animals. There's no evidence of that. I’ve talked to my African ecologist friends, and they've pointed out that  20 to 30 percent population growth rate, which is described as this aberration among feral horses and donkeys, is exactly what any ungulate population of that size does in the absence of predation.

Honestly, a lot of effects that they're talking about are the effects of any big animal. Studies have shown horses out-competing native species at water, but that’s likely because the horses where those studies were carried out were at the springs for 12 hours a day in the summer, because there were no predators to scare them off.

The idea that wild horses and burros are out-competing native species for water is built around the theory that in Africa, ungulates coexist because they've co-evolved, and so they all have very specific, ingrained times when they go to the water. And that's why they don't compete with each other. But that’s totally ludicrous. You have an ungulate species in Africa, which overlaps with 50 other ungulates species in different parts of its range, and half the time it’s migrating.

Do you think it's co-evolved with every single one of them in some way? And do you think they've coexisted in that exact community for millions of years? No, they've been moving around independently and showing up in all sorts of places. Organisms are adaptive in response.

Right. There’s constant negotiation between these different animals.

We don't know any species that is threatened or endangered by wild burros. What has actually been published, counter to the NPS claims, is that the removal of burros from this region at Ash Meadows National Wildlife Refuge led to the extinction of several endemic fish populations.


Two pretty famous ecologists at the University of New Mexico looked at this in the 1990s. You have these spring systems once connected in lakes during the last glacial period. Now they’re isolated little water bodies. Most of them are fed by the ground and don't receive overland flood disturbance. And because of that, vegetation will just fill in these areas if it can. And even if water remains in the spring, it often loses the dissolved oxygen because of the amount of dead-leaf litter going into it. Or they can entirely dry up because of the evapotranspiration of the plants. What's really interesting is that for a very long time, native peoples there  were clearing out vegetation and using it for things. And before humans arrived in these continents, big animals were as well.

But systems like in Ash Meadows National Wildlife Refuge—and also in Australia, incidentally—they fenced out and eradicated the wild donkeys. And within around 10 years, many of those endangered fish endemic populations have gone extinct, because the springs had filled in with vegetation. These landscapes are managed based on the fantasy notion of a non-peopled landscape that has no big animals. Land managers think they'll just go and manage these places themselves.

If you want to make the argument that these landscapes should be managed extensively by people, that is, of course, an argument you could make. It’s interesting to me that such a position usually doesn’t translate to, say, returning land to the peoples who have a long cultural history of doing so.

I mean, that racism is baked in now. The Timbisha Shoshone in Death Valley, they have a little placard that describes their relationships to the landscape there, their cultural practices, and it includes going to the wetlands and clearing out vegetation for wildlife, something that the burros are doing right now for free. And it's the same activity that the Park Service considers to be so abhorrent and unnatural.

How much of that resistance is rooted in aesthetics? Like, are park managers going out to the springs and saying, this place is a dump, look at all these fucking donkeys around?

I think that happens, sometimes. There are some springs that are legitimately trashed, and I'd never seen a place trashed like that by donkeys when I first came to Death Valley. These springs are right by these campsites, so they’re the things that the National Park staff see, and the things that they put on their websites to galvanize support for removing burros.

But then you walk or drive to the next spring, which is just like a kilometer away, and it's a dense willow forest with one or two trails that go in toward water.  And if you start crawling around the vegetation, you'll find signs that mountain lions are hunting these donkeys at a massive rate and it’s changing the donkey behavior. They don’t stick around for hours and trash everything.

(a) Wetland lacking both cougars and kills compared (B) a similar sized wetland nearby where cougars and kills were present. Photos were taken at a similar distance from water's edge. Public Domain, Erick Lundgren 

Your team’s most recent paper lays out pretty clearly that in areas where mountain lions are active predators, a lot of the worst impacts of burros just don’t happen, because rather than hanging around wetlands day and night they’re coming in, snatching a drink, and getting the hell out.

It’s like we talked about the cattle earlier, you know? The effects of donkeys are not fundamental to them as a native or non-native species, or to their biology. It's a response to the conditions they're living in, to predation, to social dynamics.

There seems to be a lot of resistance to the idea that mountain lions could be important predators for feral donkeys and horses, in part because—the thinking goes—they’re too small. Which seems reasonable on the face of it, but also doesn’t recognizing the possibility that ecosystem interactions can change. That the cats can learn, for example.

Definitely. The weird thing is that people have known that burros have predators, but they still claim they have no natural predators. It's a bunch of doublespeak. There have been studies showing that mountain lions can basically prevent population growth in wild horses. But those studies just don't get cited. Instead you get a ton of papers claiming that they have no natural predators and thus need to be removed by humans—and if they have a citation, they're citing someone else's introduction from decades ago. It's just not true.

I've had these conversations with biologists, smart biologists, where they'll say things like: Oh, there's no way there would have been wolves in this landscape. Or: There's no way mountain lions can hunt horses effectively, because horses’ eyesight is too good. They’re making these statements, but with nothing to back it up. And to give them some benefit of the doubt, a lot of the research done on these animals happened in the 1970s in Nevada and Arizona, where mountain lions were heavily killed to protect the livestock industry. So it was done in contexts where there weren't predators, because we had killed them all.

Today, mountain lions remain heavily persecuted in many areas. So it's not surprising if you’re studying a population of wild horse or wild donkey that they aren't experiencing predation, even if there are mountain lions in the landscape. That doesn't mean mountain lions wouldn't be able to hunt them if we stopped killing those lions.

A mountain lion crouches over a feral burro. Michael Lundgren.

In Death Valley they certainly do, as your team’s recent paper shows.

There was a remarkable, really exciting paper that was published in The Journal of Wildlife Management. They had collared lions in the desert in Nevada, and found these lions—the females especially—were specializing in wild horses, the females especially were almost exclusively eating wild horses. And that’s a landscape where we're still killing mountain lions at heavy rates to protect livestock. So if it can happen there, it’s probably happening everywhere. And it feels like the false claims may start to become harder and harder to make, hopefully.

Could you talk a bit more about the idea that feral equids are rewiring ecosystems?

Prior to widespread human impact, ecosystems were far more connected. There were far more interactions, energy flows, in organisms that were in relationship with each other. And introductions have put these animals back into these places, but some of them are disconnected, energetically, from predators, because we're killing those predators, or maybe the landscape’s predators are too small to hunt them.

So rewiring is the idea that connections and relationships start to emerge between these isolated animals. And that has implications for how those organisms affect the environment, what happens to the energy in those organisms’ bodies: you have predators that are killing those donkeys, and then those donkeys are becoming this food for mini-scavengers, and nutrients for trees, and for vegetation. Rewiring is the idea of those connections rebuilding themselves, even in a novel system.

I recall reading that mountain lions probably weren’t hunting equids much in the Pleistocene, because there are all these other big predators on the landscape—saber-tooth cats, for example—that were.

That’s our best understanding. Mountain lion fossils are pretty rare, relative to things like saber-toothed cats and dire wolves. Mountain lions were probably restricted to really rocky, steep, high elevation terrain, or rough terrain. I bet they were hunting equids every once in a while, but they probably weren't a major predator at the time, which supports people claiming that mountain lions wouldn't be able to influence horses or donkeys. The fact that they are suggests that things are way more flexible and fluid and dynamic than we usually think.

So I think all of this kind of comes down to divergent worldviews in ecology and evolution. On one side, you have people that insist that ecosystems and organisms are the product of millions of years of coevolution, which created these very rigid relationships between organisms and capacities within organisms — that mountain lions co-evolved with deer, and that's all they eat, and they won't learn to eat something else. And, in this worldview, if a new species shows up, or you take one species out, the whole system falls apart.

But another worldview is that these relationships are far more dynamic — that mountain lions are actually cultural beings. They have certain capacities physiologically, but they can learn how to hunt harder prey, if given the chance.

And we're also seeing that evolution in terms of physiological traits of organisms is way more plastic than we think. There's a great paper recently from Florida where a large snail got introduced and pretty much replaced a snail that was about 25 percent smaller. And it was going to cause the extinction of the snail kite in Florida. Snail kites dropped [to] almost nothing in population. Then, within 50 years, snail kites were about 25 percent larger, and all they eat is this introduced snail, and they actually have way better reproductive success in areas with the introduced snail than in areas with only the native snail.

Snail kite, Andreas Trepte.

A 25 percent body mass increase in 50 years in a vertebrate is quite incredible. So I think this other worldview—that relationships can be really dynamic—is more supported by evidence. I think that the idea of rigid and slow evolutionary history, with organisms as artifacts of these deep-time processes, is more of a cultural reflection of certain ideas about Eden, purity, and about stasis. I don't think they're actually biologically grounded.

There are interesting claims coming out of Australia, around the notion that feral outback cats are potentially growing to larger sizes and tackling larger prey. There’s some genuine scientific work that needs to be done to clarify whether that’s happening, and certainly some of the photos employ a lot of camera trickery. But it doesn’t seem impossible for feral cats to go off on their own evolutionary trajectory.

What do you think the evolutionary possibilities are for some of these animals once they’re out on the landscape?

It’s such an interesting question. Not to circle back too much, but back when I was an undergrad, I was a fervent, rabid invasion biologist.

Define that term real quick?

There's a discipline called invasion biology which studies introduced species, particularly species that are introduced and that are doing really well, which are called invasive species — invaders. The anthropomorphic and emotive language in the field is quite astounding. A lot of the work of invasion biology has been to document the effects of introduced species, and then to figure out ways to kill them better.

And I was an invasion biologist. I was out there with my ax, chopping out introduced honeysuckle from these nature preserves in Indiana feeling really proud of myself. I was putting my own ego into that work, the way I was scapegoating these plants for what else was happening in the world.

But what really changed my view on invasion biology was my dad. I pointed out a span of invasive honeysuckle on a nearby property to where he lived, and how we should go and kill it. And he was like: Well, I wonder what their future here is? And that completely changed my intellectual stance toward these organisms. What is their future? We’re not going to get rid of them. There's not going to be an upwelling of all the citizenry of the world going out and chopping and poisoning all these introduced plants, and introducing organisms like donkeys. So what is their future? What does the world look like in the future?

An Australian feral cat takes a wallaby, NT Department of Environment and Natural Resources

It's nothing new for organisms to disperse across all geographic barriers. In fact, that's how biodiversity emerges. The processes that engender new species are the processes of immigration, which you could call invasion. So what does the future of biodiversity look like if we actually treat these human-introduced organisms as organisms?

To bring it back to the cats in Australia, I’m fascinated by that question. The only way to get rid of them is something really barbaric and draconian, like gene editing technology, or paintball machines that identify cats and then shoot them with a poison-filled paintball. Which they’re putting out in Australia. We could spend billions of dollars doing that and maybe, maybe we could eradicate cats. Probably cats are there to stay.

And I don't know about you, but I find it very discomforting that we unleashed technology, like CRISPR gene editing to cause extinctions. Once we start doing that, we've opened Pandora's box to a type of relationship with a world that I think is really, really dangerous.

We're pretty good at wiping out species already. Anything that makes that easier I think is worth viewing with real alarm.

One of the crazy things is that feral cats and introduced red foxes in Australia are considered some of the top invasive species, and are blamed for causing the endangerment and extinction of small mammals there. And there might some  truth to that.

But remarkably, my colleagues and I are working on this evidence review right now, where we’re going through every single citation making that claim. And there is no actual evidence! It's all papers citing other people's claims. It's just a big circle of claims of people saying that these cats are a leading cause of extinction. But it doesn't go back to any data.

There isn't even evidence of cats being removed from a given island and the native species increasing. And if it did, that's exactly what you'd expect with any predator being removed, whether native or introduced. That’s the major philosophical issue in invasion biology: because the species is introduced, you act like its effects are aberrant, but its effects are actually exactly the same as any other similar species, native or otherwise.

I’m very curious—and I’ve written about this in the past—about the exotic animal ranches in Texas, which have a ton of different herbivores out on the rangeland. There are introduced herbivores like Axis deer in the Hill Country, or these big Indian antelope, nilgai, that live out on ranchlands and parks in the Lower Rio Grande Valley. Which, anecdotally, mountain lions seem to target as well.

But there doesn’t seem to have been much practical fieldwork done on these rangelands that now host multiple species of ungulates, and some large flightless birds. What are the relationships happening on those landscapes?

No, I don't think it's being done, remarkably.

A Nilgai on Cotton Mesa ranch, Texas.

Really? Because it just seems like a killer PhD project.

Especially if you had ranches with differing assemblages that were in the same landscape, which would be awesome. There would be so much good science there. When that Pleistocene rewilding paper came out in 2005, people called for these types of research questions, but no one picked it up. They were just widely ridiculed and attacked for asking these questions, and then no one followed up on it.

Do you think that there are any circumstances in which targeted culls have some value?

I—well. I would love to say absolutely not. But I think ungulates on islands can lead to an island that was once lush becoming a desert. Like feral goats.

But the thing is, that process has never been studied to my satisfaction, because there's all sorts of variation in that. You have islands with feral goats that are still super lush. How? Where goats are low density, there's no predation, super lush. How is that? If you look at the fossil record, we know that ungulates got to the islands without predators many times in the past, and they evolved in all sorts of wild ways to reproduce less frequently, to have fewer babies, and to live longer.

There's this conflict, I think, in ecology and conservation between research and management. And we frequently just jump to management and we don't ask questions. We stop being curious and wonder about these systems. Like what is the future of those feral goats?

For six million years, there were these goat-like animals on barren islands in the Mediterranean that grew like reptiles—intermittent growth—which no mammal has. When a species of deer got to Crete it split into eight species, from 10 kilograms to 300 kilograms. No predators on the island as far as we know, and they got by. Those are the processes that are so interesting.

But if you love a place and you see goats turning from a forest into a dusty, dry landscape with much less biodiversity — it's really hard to just accept that out of academic curiosity. So I think it's a complex thing. But we often knee-jerk resort to killing even if there isn't a problem.   There's an island off in Australia, super-lush, low-population of goats, no evidence that they're harming anything. No science has been done on it. But they captured some dingoes from the mainland, injected little poison bombs in the bodies of the dingoes that would go off after six months or a year, and then introduced them into the island to kill the goats. That is just — that's like, sadism. That's just absolutely sociopathic to me!

Obviously ecosystems aren’t mechanized and predictable, but if you're worried that there's nothing there to control the goats, then theoretically, you could just introduce the predator and wait to see what happens.

I’m not against that. San Nicolas, one of the Channel Islands off California, had feral sheep and goats, but it also had feral dogs until the ranchers killed them all. And then the island became de-vegetated. In Hawaii, there are feral dogs up in the mountains — the future Hawaiian Wolf, you could say — that hunt the feral goats and sheep. But the conservationists go and shoot them first.

I'm fascinated by that future ecosystem where there's Hawaiian goats and Hawaiian wolves. That’s so interesting.

Yeah, they're not going anywhere. They're on an island. They’re stuck. That makes me wonder—what are some other ecosystems you’d like to study if you had a time machine?

I would love to study feral pigs! [Laughs]

A small sounder of feral hogs. Public domain, U.S. Fish and Wildlife Service

Talk about a maligned species.

I think feral pigs are really fascinating. They're one of the most hated animals. You can't read about them without reading the words: “devastate”; “destroy”; “marauders.” Everything about them is dripping with animosity. But these are very intelligent animals.

You know, I’m working on this huge meta-analysis actually comparing the effects of introduced herbivores versus native herbivores, and the results are pretty astounding. Nativeness does not matter one bit. One of the most remarkable things about it is how different the actual effects of pigs are from our description of the effects of pigs.

How so?

In the Smoky Mountains in Tennessee, pigs were found to increase tree growth rates by increasing nutrient availability by turning leaf litter into the soil. In Australia, pigs root these areas under these fruiting, masting trees, and because they did that, the fruits and the termites and the bugs become more available to birds. So you get these huge flocks of birds that forage selectively in these areas of pigs have rooted.

Most studies show if you look at an area that was rooted by pigs versus an area that wasn’t, and you track it over time, you get these kinds of results. People say that they reduce plant richness to zero. Well, yeah! They had just rooted it. But if you look back in a year, that place that they rooted is three times more diverse in terms of plants than the place next door that wasn’t. So there's evidence actually points to most of their effects [being] quite positive in all the ways we would call something positive. But yet we hate them so much.

They do eat a couple billion dollars worth of crops, which tends to really annoy people in my experience.

So let's be honest about that! If it's a human-wildlife conflict, it’s no different than elephants and crops. And let's leave the invasion biology rhetoric out of it. I guess a future ecosystem I would be fascinated in studying would be the Hawaiian islands with feral pigs and feral dogs, and nobody messing with either of them.

I would love to see the evolutionary trajectory of feral pigs on an island. Give it a million years or so and things would get wild.

I know. Actually, preferably it would be an archipelago. Some of the islands have wolves — the future wolf, former dog — and some of them don't. And what happens with the pigs when they don’t? Are they gonna evolve to breed more rarely? To live longer? Do they get smaller or do they get huge? What happens?

The elephant pigs of the future Hawaiian archipelago.

I like that! What you're broaching, too, is really important: ecologists have been so backwards looking. But we need to think about the future. And conservation, too, should think about the future. Like, is it worth doing things that won’t make a difference in 1000 years?

I think that's such a difficult thought, just because everybody in conservation feels very squeezed. The seems to be that, well, there’s so little left. So how can you even think about taking a chance on the stuff that isn't currently a housing development?

Well, instead of trying to purify what isn’t housing development, stop making new housing developments! Put that energy into real urbanism. Our suburban growth is killing us and destroying these landscapes, and conservationists are out there spraying herbicide in wild landscapes instead of stopping them from becoming another suburb. I just think it’s a distraction from the fundamental drivers.

But also, I think we should recognize that any native wild landscape that you care about is not going to look like that in 100 years, at the rate climate change is going. We’re heading towards a world like the Eocene, when there were temperate forests in Greenland, and Northern Europe was tropical. So we’re going toward something very different. [Laughs.]

“Turn and face the strange,” as the poet said. So what’s next on the docket for you?

I’ve got one more paper from Death Valley that I need to finish, as well as the big meta-analysis  on introduced herbivores versus native herbivores.

I've also got some really interesting field projects. I’ve got a project with feral donkeys, which are displaying some capacity to revegetate abandoned farms through seed dispersal. Abandoned farms in the desert really do not recover quickly, and they've turned an abandoned farm into a mesquite forest in like 10 years, which is unheard of.

I’m also interested in migration, which is one of the things—like predation— that structures how herbivores impact a place. It’s a cultural phenomenon of knowing the landscape at a large enough scale to actually move across it. So you can have 10,000 horses graze a place for a week, and then they go somewhere else for the rest of the year. And that both engineers local systems and reduces overall grazing pressure.

I've seen some preliminary field observations of these huge mobs of wild horses  moving across these Nevada deserts en masse, going somewhere, and then disappearing off into the fucking vastness again. I want to study that!

Dinosaur paleontology is my first love, so that just makes me think of these Mesozoic ecosystems where—presumably—truly enormous sauropods could roll in, wreck everything, and maybe not return for years at a time.  

Right?  And that kind of episodic disturbance seems to be really key for many things. A lot of plants require disturbance to germinate, so you have this break in the forest, so other plants get a chance to grow up more competitively.

There’s also nutrient movement and seed movement, which is really critical right now with climate change. Someone in my lab in Denmark did an analysis, and I believe their results showed that plants need to move some 40 kilometers a year to keep up with climate change right now. And native deer and pronghorn, as it stands, I don't think they’re going to do that.

You feel like horses might?

These movements I’ve been seeing in wild horses are huge, and they're moving lots of material. Pronghorns and ruminants also don’t digest things the same way—their systems process things much more thoroughly. There are many seeds that aren't going to survive that, compared to their chances with a hindgut fermenter like a horse. I think that that is an interesting component.

What I find most exciting about all of this is that people have started bringing animals into how we understand the earth as a  system. And in that system, animals are kind of the blood in the veins, moving nutrients and seeds that would otherwise just flow downhill, or where the wind takes takes them. But animals are able to go against these natural gradients and pump things across the landscape.

The heart, you might say.

Yeah. The heart and the blood of the earth.

Thanks so much for joining us, Erick.

Any time.

Erick Lundgren is a wildlife biologist at Denmark's Aarhus University. You can read his papers at his website, follow him on twitter at @ejlundyyy, or shoot him an email at erick.lundgren@gmail.com.

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