Is humanity the most damaging predator on Earth? Many experts say yes and that its predatory practices maybe disrupting evolution. Maria Armoudian speaks with three researchers who have looked at this issue: Chris Darimont, Tom Reimchen, and Heather Bryan.
Chris Darimont is a Conservation Scientist at the University of Victoria, BC.
Tom Reimchen is a Professor in Evolution at the University of Victoria, BC.
Heather Bryan is a Postdoctoral Fellow in Applied Conservation Science at the University of Victoria, BC.
I thought perhaps we could start with the origins of the study which I understand is from this history of the idea of sustainability. Tom Reimchen this is your area. How did this originate?
Tom Reimchen: It sort of his rooted in a field study that I began in 1975 in a very remote lake on the west coast of Canada. I was trying to basically evaluate some pretty basic ecological processes in this lake where I was studying this small fish called the stickleback. And I found that there were about 22 species of predators that were utilising this small fish and they included…trout and otters. And I built up quantitatively a sort of a total consumption for each of these twenty-two species of predators. And very simply I found that none of the predators really took even up to five percent, it was usually one to five percent of the prey population. And I thought that was sort of interesting that there were so many predators but they were taking such a small amount when it seemed they could have taken a lot more. And also, virtually none of them were taking the adult fish, they were always taking the young ones. This seemed to contrast dramatically with what I could see in adjacent marine waters where human fishers were taking individually about fifty percent of the total prey biomass of herring, salmon, and we were targeting the reproductive adults. And this fundamental disconnect between us as a predator versus all these natural predators which obviously had persisted in these communities for a long time set in motion the origins of this paper.
One of the ideas is how we define sustainability and how we research sustainability according to your paper. What had been the general definition of sustainability with regards to these ecosystems before and how had they been studied?
Chris Darimont: When a new student in a fisheries class, for example, first hears his or hers first lesson on sustainable exploitation, what he or she listens to is a model or idea that speaks to sustaining the yields to humanity, that is harvest, that is maximising the long-term steady-state bio-mas that flows out of ecosystems into humans. And that has served humanity awfully well in the past few decades, but it is becoming clear that that sort of bio-mass removal clearly has cost to ecosystems and it contrasts very much with the ideas that Tom just spoke to, and the idea that non-human predators, these natural predators can serve as models of sustainable exploitation. After all they have stood the test of time in by and large not having the drastic impacts on populations that we humans do.
When you study the predators in terms of human predation it seemed you focussed primarily on non-huge commercial types of farms, right? This is out in wild areas?
Heather Bryan: This again comes from Tom’s original idea that we might shift our idea of sustainability to one that involves looking at natural predators that have evolved for millennia with their prey as examples of sustainability. And so what we did is we compared the rate at which humans exploit wild species and compared them with the rate at which natural predators in both marine and terrestrial ecosystems exploit wild species. And we looked at ecosystems spanning the entire plant, drawing on published studies mostly from the 1990s and we were able to compare both marine and terrestrial systems which is something that many other studies haven’t tackled.
Human predators they tend to first of all be more damaging than other predators. Let’s go through why that is.
CD: Humans have evolved culturally, technologically, economically insofar to become to what we refer to as the super predator, this predator of predators which is a key finding in our paper: a predator with remarkable ecological and evolutionary costs to ecosystems. And there are several tipping point moments over time, probably starting a long, long time ago with the development of projectile weapons, starting with simple throwing utensils that could despatch an animal without having to engage with it. Predators lead very dangerous lifestyles in that they often have to physically interact with prey and that can sometimes lead to their demise. So that was an early game-changer. Fast forward to say the 1940s and 50s where marine technology, industrial fishboats had the capacity to stay out at sea and freeze fish out at sea, was another game-changer in that no longer would they have to cut their predatory mission short and head back to market so the fish could be frozen. And it just hasn’t stopped since then with global trade in seafood products. Some remarkable technologies allow us to search, pursue, and capture prey. I’m thinking for example of spotting planes that fly above the oceans in Alaska looking for herring balls that direct boats on the waters to those schools of fish; thinking of giant nets that can scour the ocean floor; I’m thinking of large projectile weapons that can bring down a large carnivore from almost half a mile away. These are remarkable technological accomplishments but they have had enormous ecological costs to the prey we exploit and the ecosystems that ultimately support us.
TR: There are two additional issues and that is the millions of years of adaptation that prey have coexisted and coevolved with their predators have led to this sort of litany of huge behavioural adaptations, morphological activity all basically to cope with and minimise the likelihood of a sort of successful predatory event. But as this works, predators coevolve. And so what we see in the real world is this balance, this sort of equilibrium and there is no adaptation that any prey have that basically is free of our skill set. So basically, these prey here have now encountered this predator from which the last million years have provided no sort of capacity to cope with.
And the other thing that makes us a particularly dramatic predator that differs from so many others which we have alluded to here and that is that we tend to target the reproductive capital is this disconnect with what we find with the vast majority of these other predators which have targeted the reproductive interest. An obviously the metaphor here is not that complicated but is quite profound: no system will persist if the capital is continually targeted and that is the main target of our capture. And so this is ultimately part and parcel of the complete lack of sustainability.
One of the things that you have found in your paper is that people target the large, the big, rather than the juveniles. Is that what you are talking about when you talk about reproductive capital?
TR: Yes, it is. In fisheries we have this concept called ‘yield per recruit’. It doesn’t make any sense to catch a baby because if you let it live another year it would be much heavier and if you let it live another year it is going to be even heavier yet. So you can very easily model a situation in where what is most cost effective is where you have the maximum yield basically for any individual. And that basically is coincidental with the entry into the adult-sized classes, which is the reproductive capital. So it is the nature of our fishing science that almost invariably demands that we target the reproductive classes.
That has a negative impact on culling than other animals. This is primarily hunters and fishers, but what if we extended that out to other ways that animals were used by humanity?
HB: I guess if you think about it from the perspective of how we use domestic animals, we have selected for desirable traits over hundreds of years that allow us to benefit from products like milk, selecting for higher milk production and traits that ultimately benefit us. Whereas, in wild populations we can see some of the facts of our harvesting that have potentially negative evolutionary effects on populations. So the sort of comparison but also the example of how we differ in terms of different types of impacts that we can have on animals.
And what about the quantification? You have some numbers in terms of how different the rates are between us, the super predators, and others.
HB: The most striking findings were from marine systems where we take about fourteen times higher prey from the oceans compared with single species of natural predator, which is fairly dramatic. And in some cases, we take much higher than single species of natural predator. What was interesting on land was that although we didn’t take more overall compared with single species of natural predators we differed in how we take species on different trophic levels. So if you actually looked at some of the large carnivores we take up to nine times the typical rate of natural predators, and natural predators that are large carnivores tend to be other large carnivores.
There are two types of impacts that we have been talking about. One is about the evolutionary shifts, another is potential extinctions, and then a third one seems to be about global food chains. So how can we break out these consequences from this super predator type of activity?
CD: Well, clearly human predators have emerged as a pretty potent agent of evolution both in the macro sense in that over-exploitation has led to a major evolutionary process, that is extinction over the last few thousands of years since we have evolved as proficient hunters. But you mentioned something really interesting and that is the more subtle microevolutionary changes, that is to say changes that happen on contemporary sort of timescales. In fishes we are seeing effects like shrinking size and age, that is fishes are getting smaller at a given age than they once were even a decade or two ago, or effects like shrinking horns on big-horned sheep and so on. And also in the marine world, shifts in reproductive schedules: fishes are beginning to breed at younger ages and at smaller sizes and all this is precipitated by the very different phenotypic targets or targets of selection that hunters and fishers impose on that reproductive capital which gives a selective advantage to those individual fish that grow slower, that reproduce early and get some reproduction done before they enter the large size classes, and they have very low probabilities of surviving another year. And another interaction between evolution and ecology is when fishes in particular are breeding earlier and at smaller sizes they tend to have less offspring and that can have a demographic effect on populations – populations that breed earlier because of our evolutionary forcing tend to be less resilient in the face of continual heavy harvest.
Lets bring this back to where we started. Given the study’s findings should we redefine sustainability and if so how?
TR: Well, if we continue to harvest the capital at the rates we are there is no such sustainability possible at the community level. We will probably likely have seen the gradual erosion of the numbers of all the competitors so we can contain high levels at the expense of these other species. So if we are talking about ecological sustainability in the long-term where the entire community persists, clearly what we have to do is we have to shift down to quotas that are representative of what we find in other predators and that is typically less than five percent, and we have to shift to obviously the size classes that are in fact representative of the typical set of what we call the J-shape survivorship curve is in so many fishes. And so if we embed ourselves among those, then I believe long-term sustainability is probably a fait accompli, but without those changes you can micro-manage indefinitely but there will also be no solutions without those two initial changes that we have talked about.
CD: Tom brings up some excellent points and some guidance from non-human predators, that is: target the young if possible and don’t take too much, these are simple rules that most non-human predators that have persisted in ecological communities for millennia or millions of years demonstrate for humanity. And I acknowledge, and we all acknowledge, that there are enormous cultural and economic barriers against such shifts. But that being said some fisheries show great promise in for example shifting the harvest target to juvenile size classes.
Towards the end of your paper you had a list of potential solutions and some of them would probably need some explanation, like cultivating tolerance for carnivores which I thought was interesting. Why don’t we talk about that as well within this context. What do you mean by tolerance for carnivores?
CD: We think the solutions are much more clear cut in terms of safeguarding large carnivore populations into the future. Although there are economic drivers of those harvests, there is much more opposition to harvests. That is to say the social licence that society once granted to trophy hunters is quickly eroding, and the global moral outrage shown after Cecil the lion was killed sends a signal that this is indeed true. So what managers and campaigners and conservationists can do is help society change policy about large carnivore hunting to reflect what most members of societies believe to be a hunting activity that belongs in the history books and not in a day and age where large carnivores are so quickly disappearing.
And another potential solution that you put forward in your paper was supporting community leadership in fisheries. What does that mean?
CD: In fisheries management you can study the fish till the cows come home – or the salmon come home – but often good management comes down to managing people and in a global meta-analysis published three or four years ago the common denominator in well-managed fisheries that haven’t been diminished like so many others is local leadership and management on local scales, decentralised management so that humans are managing resources in their backyards or back lakes or near shore waters, for example. And they will tend to make good decisions when there are leaders and communities that recognise the long view, a view that doesn’t overexploit the reproductive capital at the expense of that capital for the future of human generations. That would be another step in the right direction.
Would it also be a step in the right direction to decrease the consumption of these animals? I have read in some of the IPCC and other climatology reports that our desire for eating so much meat is actually bad for the climate, it sounds like it is also bad for our fisheries and everything else. What about some proposal to that effect?
CD: Clearly, especially set against the background of a still rapidly increasing human population that in fact is not decreasing its demand for meats, any social management or marketing process that can ease the demand for wild food will certainly do our populations a favour. But there are some awfully big economic and cultural processes happening that make that unlikely. So I am afraid my view on that is not overly optimistic, but I expect, and this was not the intention of our paper but I expect when people think about predators now I hope they think about humanity and they think about what maybe staring at them from their dinner plates and might start to ponder what some of the ecological and evolutionary costs of those meals might be.
This interview was originally aired on the Scholars’ Circle. To access our archive of episodes and download this interview click here.