After a magazine dedicated entirely to particularly invasive plants and animals, it’s time to meet the people. We met up with Professor Yohay Carmel and Professor Assaf Schwartz to discuss invasive species – the damage, treatment, xenophobia, and myths.
Photo by Roni Frenkel
Professor Yohay Carmel – brief biography
Prof. Yohay Carmel joined the Technion in 2000 and established the Ecology Lab in the Faculty of Civil and Environmental Engineering. His research focuses on diverse topics, including natural resource management, spatial patterns of biodiversity, fire risk models and the evolution of human society. Many of his studies take place in collaboration with the Israel Nature and Parks Authority (INPA), Keren Kayemeth LeIsrael (KKL) and the Ministry for Environmental Protection. He has served as Chairperson of the Israel Society of Ecology and Environmental Sciences and Chairperson of the Scientific Committee of KKL.
Professor Assaf Schwartz – Brief Biography
Prof. Assaf Schwartz joined the Technion in 2014 and established the Human and Biodiversity Research Lab in the Faculty of Architecture and Town Planning.
Assaf’s research examines how human activity affects the natural environment, and the economic and other advantages of conserving nature, seeking to formulate solutions for sustainable planning and management of disturbed (farmlands, cities) and natural (nature reserves) environments for the shared benefit of humans and nature. In other words, this is interdisciplinary research that combines ecology with geography, sociology, psychology, economics, planning, and more.
When you’re pregnant, everyone arounds you seems to be pregnant, when you’re on a diet, everyone is suddenly on a diet, and when you write about invasive species – it seems that everyone is studying invasive species. It takes you a few moments to remember that until a few weeks ago, just like most other people, you didn’t know anything about them.
How do you explain this gap?
‘When a tractor comes to flatten the land, it’s clear that nature is being destroyed. When a plot of land becomes a building it’s clear that nature is being destroyed. But when something happens very quietly – a bird arrives, reproduces, and competes with local species, it takes us much longer to detect it,’ Assaf explains.
‘The myna, for example, which reached Israel 20 years ago, has become one of the most common species, in most parts of the country, while other species are in decline. It’s very difficult to prove empirically that the myna is the main cause of this decline, but cumulative circumstantial evidence causes us to think and realise that these species are completely changing the face of the ecological community.’
And now we must ask – is this is a good thing or not?
The life of an animal vs. biodiversity
Prof. Yohay Carmel and Prof. Assaf Schwartz share the same laboratory and generally share similar opinions and outlooks. The only subject that they disagree on is invasive species.
‘I don’t dispute the facts,’ states Yohay, ‘there are invasive species. Some of them cause a decline in the populations of other species, sometimes to the point of local extinction. We have no absolute proof that this is the reason, because there are other reasons for species decline and extinction, such as establishment of neighbourhoods and forest clearing, but undoubtedly the decline in the populations of local species, at least in part, is the result of invasive species.
‘If we were talking about a person, then based on circumstantial evidence we would not sentence him or her to death,’ says Yohay, ‘but since we’re talking about a bird, some people are trigger-happy. I want you to know that the myna is an intelligent being, probably no less than other birds (otherwise it wouldn’t be so successful), so we need to think about whether it’s legitimate to harm it. I believe not.’
‘So in fact we have a clash between two values,’ Yohay emphasises, ‘the first value is biodiversity and the second value is the life of an animal (an expansion of the value of human life). The value of an animal’s life changes with time just like the value of human life changes. For example, once the life of a slave had very low value; today this is not acceptable. This is clash between two values, because for nature lovers both of these values are important.’
‘In the context of harm to invasive species, I cannot unequivocally prove that their invasion causes humans to suffer, and no-one has been able to show that shooting mynas solves the problem entirely, thus the solution of killing mynas cannot be justified in my opinion. You can’t justify killing a species just because it’s invasive.’
We have only a small area in which we can protect nature, and if we don’t manage it, we’ll lose species. So we must manage actively.
It’s not easy to be a sparrow
‘And what about the animals that are harmed?’ asks Assaf and challenges Yohay, ‘Don’t they have any rights? The myna was introduced to the system by humans – don’t we have a responsibility to protect the sparrows from it? In the case of the sparrows, we’re talking about more than a circumstantial chain of events. The aggressive behaviour of the mynas towards the sparrows is known – predation on chicks, a decline in the number of sparrows wherever mynas are present (in a study in the Yarkon Park, the sparrow population declined from 400 in the past to only 16 currently, while the number of mynas keeps rising), so I ask, doesn’t the sparrow deserve protection?’
I want to answer you with a basic ethics principle,’ replies Yohay, ‘When I choose to shoot at a myna I am directly causing it to die. When humans brought the mynas, they did not directly cause death. No one introduced the mynas in order to harm the sparrows, there was no direct intervention here. It’s not easy to be a sparrow,’ emphasises Yohay, ‘even crows prey on sparrow chicks, as do cats. The life of a sparrow is challenging even without mynas; even so, we wouldn’t think of intervening. So is it only because humans brought the myna that we have to take responsibility and start managing the food web of the birds and determine who lives and who dies? The private life of the sparrow is none of our business, and from a scientific standpoint there is no reason to intervene. It’s not that the sparrows are endangered. Even if locally in Yarkon Park they have declined significantly, that isn’t the situation in general.’
We are obligated to try to protect the ecological balance in the nature reserves as much as we understand it, and intervene, but here too, it must be done as sensitively as possible without causing unnecessary suffering to animals.
The precautionary principle
In response to Yohay, Assaf says with a stiff smile, ‘Here Yohay and I disagree. In my opinion we must act according to the precautionary principle. If we wait until the last sparrows and tits remain, the species may go extinct and it will be too late to have any effect; therefore, we must be cautious. We don’t have the right to intervene recklessly, but I think we are responsible for the situation and we cannot remain indifferent and wait until it’s too late. We brought these species here, to a new environment in which they thrive, because we provide them with many resources and because they were able to get rid of competitors, diseases and parasites that naturally regulate populations in these species’ original habitats. The problem begins when some of these same species begin to displace local species and endanger them; as I already mentioned, this goes on under the radar.
‘Nevertheless, the point of contention between us,’ adds Assaf, ‘often relates to “whether”, when and how to act. For example, nature reserves are the main tool for nature conservation in Israel and around the world, and we invest many resources to ensure they protect local biodiversity. When we detect, in those same nature reserves, that there is a decline in a certain species vs. an extreme rise in invaders, and mounting evidence, even of the most circumstantial kind, of a mechanism that allows the invaders to displace the local species, in my opinion it is our obligation to consider intervention, even lethal action (including culling). Of course it is very important to monitor and study the effects, examine the effectiveness of the management tool and strive to reduce the spread of the invasive species as much as possible without culling. For example, let’s try to reduce rubbish before we try to eliminate some invasive species or another. Let’s try to reconsider gardening in the areas adjacent to the nature reserves; and many other creative ideas. But in the case where we cannot find an effective solution, we must also have mercy on the local species. We are obligated to try to protect the ecological balance in the nature reserves as much as we understand it, and intervene, but here too, it must be done as sensitively as possible without causing unnecessary suffering to animals.
‘At Ramat Hanadiv, for example, during the last year we conducted a research study which included an experiment that raised many emotions. Much circumstantial evidence had accumulated regarding harm caused by mynas to several other species, including the lesser kestrel, a species that Ramat Hanadiv is taking great efforts to protect. In the experiment we tried to determine whether mynas could be thinned effectively. Over a period of one month we removed a large number of mynas from the nature park; subsequently, we found that the number of individual mynas in the park decreased significantly, while the number of mynas in the region (in Zichron Ya’akov, for example) kept rising.
‘And how long will it take for the mynas to return to Ramat Hanadiv?’ Yohay counters with a smile.
‘The truth is, we thought they’d return very quickly, but we were surprised; for almost a year there were no mynas at Ramat Hanadiv. In addition, in a behavioural study that we conducted we found that monitored individuals were much more sensitive to human activity; this may affect their ability to survive and reproduce. Nevertheless, we did not study the effect of our management action on the local species and this is a very important point. It is relatively easy to remove the mynas from the system, but if crows or other local species take their place and cause ecological damage, our loss will exceed our profit,’ Assaf replies modestly
As humans we have created new environments and we must familiarize ourselves with and accept some of the species. Botanists do it better than us: the carob and the mulberry are also not local and they are accepted by botanists and that’s a good thing.
Learning from the botanists
‘I must mention,’ says Assaf, ‘that my opinions used to be very different to Yohay’s. In my opinion, the division was between goodies (local species) and baddies (invasive species). During my doctorate I was exposed to other opinions and approaches, and today I believe that as humans we have created new environments and we must familiarize ourselves with and accept some of the species. Botanists do it better than us: the carob and the mulberry are also not local and they are accepted by botanists and that’s a good thing. Today I think that we need to study each case on its own merits: [regarding] the myna, the rose-ringed parakeet and even the local crow, which demonstrate behaviour that systematically harms a certain species, I, in contrast to Yohay, believe that we should intervene, and if there’s no choice, even use lethal means (including culling).’
Is the disagreement between you about how to manage nature? About the role of humans as rulers, as the one that decides who is good and who is bad?
‘No,’ answers Yohay, ‘I’m with Assaf. In the situation that has developed we look at all of the human impacts. We have only a small area in which we can protect nature, and if we don’t manage it, we’ll lose species. So we must manage actively. The disagreement relates to what is allowed and what is forbidden in management. I want to raise a different topic,’ says Yohay.
‘Up to now we’ve spoken only about the ethical issue, but there is also the scientific aspect of invasive species. To my mind the issue of invasive species is a myth. There is one place in the world where invasive species will really cause irreversible extinctions of other species – small islands. If rats reach a small island with species of local birds or small mammals, the rats are expected to reproduce and the local species will disappear completely. This can happen on small, isolated islands, but they are more or less the only places on the earth where this can really happen.’
And what about the other places?
‘In the other places,’ answers Yohay, ‘there are almost no cases of an invasive species being the exclusive, sole reason for the extinction of a certain species. There are some examples, but they are isolated and negligible. However, maany ecologists present the opposite opinion, stating that “invasive species are the most severe problem after habitat destruction”, and presenting invasive species s terrible creatures; this is an absolute injustice.’
An invasive species is foreign to the landscape. We can say that we, humans, tend to label foreigners and those who are different as something bad. This, in my opinion, is the source of many conflicts between humans. Similarly, it seems that the negative attitude towards foreign species has the same origin.
How do you explain this?
‘Even scientists are not always rational,’ says Yohay, ‘An invasive species is foreign to the landscape. We can say that we, humans, tend to label foreigners and those who are different as something bad. This, in my opinion, is the source of many conflicts between humans. Similarly, it seems that the negative attitude towards foreign species has the same origin. By using the word “invasive” we have already defined the species’ role. These processes create a narrative that invasive species are a bad thing, but in fact the dialogue on invasive species is based on very little rational thinking and on a lot of emotion and prejudice.’
‘Yohay and I agree strongly on this point,’ says Assaf surprisingly. ‘I have published several papers on invasive species. My recent papers were against the mainstream; I levelled a lot of criticism at the tendency to exaggerate the danger of certain invasive species even when there is very little or no circumstantial evidence.’
‘I’m all for controlled action based on scientific evidence and monitoring. Of course, there are very few cases in which the scientific proof is strong and significant; therefore, we must act carefully, particularly in those same places with pristine nature, for example, nature reserves. I agree that to a certain extent, the magnitude of the response to invasive species is often exaggerated,’ he says carefully, ‘but it’s not a myth; it’s a real fear of the unknown or the foreigner that incites researchers and other stakeholders to call for action or to act even when the evidence is not very convincing. Here I must emphasise that until now I researched these topics abroad and not in Israel, and I am not sufficiently familiar with the local system that was developed here by INPA, for example, in recent years.
‘The cypress and the prickly pear are part of our childhood landscape,’ says Yohay, ‘We don’t view them as foreigners (neither of them are local species), so we’ve accepted them, but any newcomer is viewed as a foreigner, immigrant, and invader.’ There are many myths in ecology, according to Yohay. ‘The “competitive displacement” myth is known to all experts and amateurs in ecology. According to this approach, there is a certain number of species that can live in the same territory; every species that enters necessarily displaces another species. This ecological theory was established a hundred years ago, but a study that we conducted showed that in most cases it is not accurate. Often, when additional species arrive, there is no displacement, and species richness increases.
‘Invasive species come with relative advantages: they have no parasites and no competitors, so often there will be an initial phase in which they increase significantly while populations of other species decline, but subsequently, the situation will stabilise to a certain extent. It’s not that the sparrow and the bulbul will go extinct and disappear, and if that happens it will probably be due to destruction of the local species’ habitats rather than the presence of competitors… thus, in my opinion, the panic regarding invasive species is based on myths and emotions.’
we don’t need to judge species by their origin, in the first stage, but rather by the strength of evidence on the ecological damage they cause
And what about the little fire ant? In this very magazine we wrote that wherever there are fire ants, within a decade we won’t see other ant species. Is this also a myth?
‘No, it’s not a myth. It’s true that in the same location there won’t be any other ant species; the fire ant has relative advantages over them. But does this mean that the other ant species in Israel are in danger of extinction? The answer is no! The fire ant can only live under conditions of constant humidity. In nature, outside of gardens and farmlands, conditions aren’t suitable for the fire ant. Wherever the fire ant is absent, there is a refuge for other species.’
Are you against intervention and control of the fire ant?
‘That’s an excellent point,’ Yohay enthuses, ‘We must distinguish between real danger to humans, like fire ant stings, and imagined harm to ecosystems, which is not as terrible as it is presented and definitely not irreversible. Wherever humans suffer real harm, such as in the case of the fire ant, we must intervene, but this is not an ecological problem.
‘Here, surprisingly, we switch roles,’ says Assaf excitedly, ‘because when ecologists initially defined invasive species, there was a reference to their ecological damage. But then they took it further and began to define invasive species as those that cause damage, any kind of damage. As an ecologist, harm to humans like that caused by the fire ant doesn’t interest me; I focus on harm to biodiversity and the various species.’
‘When there’s harm, or enough circumstantial evidence of great potential for harm, I maintain that we must act sensitively, but firmly. However, we must not ignore the complexity of this issue, and definitely not the deserving, principled opinions presented by Yohay and other researchers active in nature conservation and animal welfare protection. This is a very slippery slope; the moment we begin to divide nature into good or bad, local or foreign, we enter a very complex dialogue that can serve as a double-edged sword against us; I’m not sure that as ecologists we have all of the tools to deal with this dialogue. Therefore, I think that we don’t need to judge species by their origin, in the first stage, but rather by the strength of evidence on the ecological damage they cause and the potential harm of foreign species that recently escaped or were released to nature. We should also be very cautious in both our declarations and our actions, and mostly it is important to collect information and establish our suspicions rapidly. However, at the moment that we pass a certain threshold of ecological damage, I believe that we must act, particularly in nature reserves, but of course in the most controlled and least aggressive way.’
Putting an end to it
So what message would you like to convey to the public with respect to invasive species?
‘We think we’re rational and objective,’ says Yohay, ‘but in many cases we act according to prejudices and gut feelings. We need to check ourselves thoroughly before we intervene in nature, particularly before setting out on a killing spree. We must be sure that the action is indeed justified and that it will really bring a benefit and solve the problem.’
‘First of all, it’s clear that prevention is better than any kind of intervention, and it’s also cheaper,’ says Assaf, ‘therefore, the public must understand that we all have a responsibility to follow the law and make sure that non-local species are not released to nature. Our entire discussion today is about situations in which populations have already established, spread, and caused ecological damage. I think that it is important to act, and not ignore, as we are acting today to rehabilitate destroyed habitats; even here we can say we’ll let nature do its thing, but this doesn’t always work and in any case the area remaining for nature conservation is limited. So yes, in my opinion we need to act, but with discretion, consideration and a willingness to listen to other opinions, and of course with as much compassion as possible.’
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