On social media, there appears to be a stark contrast between the attitude towards invasive species of people in North America vs people in Europe.
I know that the introduction of species has caused immense ecological damage in the past (the chestnut blight for example), to an extent that I don’t think any species has achieved in Europe. Current invasive species in North America (Spotted Lanternfly) also seem to cause more damage than any invasives in Europe. (as far as I’m aware)
Identifying ladybeetles has also revealed something which is IMO quite shocking. I’ve always had the feeling that in N. America, the majority of ladybeetle observations were of invasive or introduced species. I was curious so I decided to actually compare the numbers:
Turns out, about 65% of ladybeetles observed in the US are not native. That’s basically two thirds! These beetles belong to Harmonia axyridis (Harleqin Ladybeetle), Coccinella septempunctata (7-spot), Propylea quatuordecimpunctata (14-spot), and Hippodamia variegata (Variegated Ladybeetle).
In Europe on the other hand, about 34% of all ladybeetles observed belong to an invasive species, all of them H. axyridis.
That is still a lot, but it’s just a bit over a third. Half of what it is in N. America.
So, is species invasion more harmful in North America than it is in Europe?
And if so, what are the reasons behind this? I have a few hypotheses, but I could not find any actual research on this.
I decided to put these in a comment to not make the post too long.
Hypothesis 1: Due to the geology and the history of Europe, Asia, and Africa (trade, exploitation, etc.), European flora and fauna has been exposed to foreign species for a longer period of time than that of North America, which has lead to a higher resilience (and perhaps already completed invasion processes which nature has already adapted to)?
Hypothesis 2: North America has far larger agricultural areas with far bigger fields (monocultures), and overall less regulated use of pesticides, fertilisers, etc. (afaik), which has provided a lot of easily invadable habitats and has weakened the ecosystems more than in Europe.
Hypothesis 3: North America is overall more varied in climate and ecology than Europe, so more species from different climate zones can establish themselves there and then start to spread when environmental factors change (climate change, etc.)
These 3 hypotheses can’t really explain why American species aren’t more successful invaders in Europe, however.
Hypothesis 4: The longer and more extensive use of land by humans in Europe has caused more favourable conditions for generalist species, which are less likely to be affected by invasives and have a higher potential to become invasives themselves. In North America, where habitats have been far less affected by humans for far longer, there were/are still more specialised species, which more recently have (and have had) a hard time competing with the more generalist invasives as the habitats rapidly changed and are less likely to become invasive.
I’m not necessarily convinced invasive species are more of an issue in North America than in Europe.
But certainly one contributing factor to invasive species in NA:
Most North American ecosystems no longer have their natural disturbance regimes. Many/most ecosystems in NA are fire-dependent, a much larger percentage than European ecosystems. Invasive plants in NA thrive in human-based disturbance regimes (e.g., clearing, overgrazing, mowing, trampling), possibly because these are the types of disturbances they evolved with. However, we see far fewer invasive plants in fire-maintained habitats. (There are a few exceptions; Bromus tectorum does quite well with fire and actually disrupts the fire regime in the opposite direction, by increasing the intensity and frequency of fire beyond what is natural.) Bringing (appropriate levels of) fire back to our landscapes would limit invasives in two ways: 1) promote healthier native communities that are more able to outcompete invasives, 2) promote disturbance regimes that most invasives did not evolve to cope with.
Could you forwards some examples? I usually tend not to attribute so much authority to social media as so many types of user can write there, from experts to people that are totally beginners.
I would not bet on it. The severity of the damages done by invasives can be also influenced by climate and soil. So an invasive can be more detrimental in certain ecological conditions. Regarding chestnut, what about Dryocosmus kuriphilus in North America? Here many chestnut trees have died and are many more are going to, also because they have been planted in sites where there are no optimal conditions.
Maybe in North America there is more concern by institutions that has made people to be more aware.
The invasive problem appears worst where you are, what you look at and notice. For me - plants - stands of Australian wattle / Acacia looking me in the face, towering over my shoulders, piled up for stack burning.
Thanks to iNat yesterday I ‘found’ number 142 to add to our list of 141 wattles. Fascinating to read along beside the scientists. https://www.inaturalist.org/observations/237687192 no evidence of invasiveness yet - says daverichardson
I have no idea whether invasive species are a worse problem in north America or not, but have some idea of why the attitudes towards invasive species may be different. In Europe there are lot of countries all bordering each other, which makes any biocontrol efforts much harder. Whereas north America is a tad more isolated and only really has three countries so any attempt at biocontrol laws would at least be easier to apply. This may explain part of the difference in attitudes.
(this is certainly the case when it comes the difference between Europe and countries like Australia and New Zealand, in the latter two there are very tight regulation on what you can bring into the country)
This is just my opinion and based on my experience living in southern Europe and Australia:
If you live in a place like Australia, where Europeans first arrived permanently in 1788, or the Americas, where they did so in 1492, there is a clear cut-off point for native vs exotic taxa, and normally a fairly pervasive attitude that native=good and exotic=bad.
When you live in a place that has had people moving taxa around basically forever, for example the British Isles or Scandinavia, where people already lived before plants arrived at the end of the last glaciation, the concept of what is native and what is exotic is a little more rubbery. In Australia, just about every exotic species is considered an invasive or potentially invasive weed. In many places in Europe, the distinction between taxa that cause environmental harm and those that seem not to seems to be given more thought.
For some taxa it is clear. For example, Acacia species from Australia becoming invasive in Europe, or Monk Parakeets from South America. For others, it is impossible to know whether they are native or exotic. Where do you draw the line?
Do you consider exotic those species that were brought anew to southern Europe by Islam in the 8th–15th Centuries?
What about species spread by the Romans?
What about the Phoenicians?
What about the Celts?
Presumably even others were moved by neolithic farmers to areas previously inhabited only by hunter-gatherers. Some of those became a part of the local fauna and flora. Are they native or exotic?
Would you consider Testudo graeca native to Spain? What about chameleons? Both were probably introduced by humans in the past and both are considered endangered and protected by law…
There are several recent papers considering whether certain species should be considered native or introduced in Britain and Ireland. Two which have recently been moved to the non-native category are Snakeshead Fritillary, which has nature reserves devoted to it in England, and Strawberry Tree in SW Ireland. But such species don’t suddenly become undesirable by being designated non-native (though Strawberry Tree spoils things by being invasive in Britain). Ancient introductions are a form of archaeology. I agree there is a difference in attitude towards new and ancient introductions, with the cut-off being hard to pinpoint or define. It is similar to the difference between modern rubbish being litter and old rubbish being historical artefact.
Not necessarily. In the US, we have the Environmental Protection Agency, which is a branch of the federal government, but as far as I’m aware they can only enforce legislation that has been passed by Congress. Most environmental regulation seems to happen at the State level. I’ve actually been hearing about rolling back some of those regulations lately, at least here in Indiana. I’m not really into politics, so don’t ask me for details on how everything works, but I think it’s safe to say it’s a mess.
Or modern pictographs being vandalism and ancient pictographs being an archaeological treasure.
To some extent that has been documented in North America, too. But we distinguish between taxa moved within the Americas in precolumbian times and those brought from other continents. Do Europeans make similar distinctions regarding the Age of Exploration?
In botany it is common to talk about archaeophytes for species that are long established but were originally brought to a particular part of Europe by humans in pre-modern times.
Thanks for explaining! I don’t live in America so it’s easy to forget how similar the states are to being their own country.
Hopefully someone else has some more insights on this topic, it’s very interesting.
I honestly don’t know, though there is research on the impact of invasives on different regions, perhaps that is a good place to look? In southern Africa invasive species are a similar sized threat to biodiversity as habitat loss. In the case of invasive plants such as Acacia, Lantana, and Eupatorium, invasive species and habitat loss are the same thing!
Certainly in my experience people in Europe care much much less about invasives (several are even seen as a positive), as in contrast to South Africa, for NA I couldn’t compare.
I think in Europe the waters are certainly muddied because of older (though still historical) introductions. Europe has also been a thoroughly human landscape for thousands of years, very few areas have not been at some time felled, ploughed, grazed, or otherwise plundered, so I think any hopes of maintaining some kind of ‘pristine’ state are long gone. Whereas for example, and I assume this applies to NA, some swamps, jungles, deserts, and plains in southern Africa have been relatively un-humanised (though not completely!) because of endemic diseases or resource pressures for example.
It’s quite frustrating, but hopefully with a new interest in habitat restoration/rewilding we Europeans will realise what we are missing, what doesn’t help us, and what we have to look forward to!
i am not sure invasive species are less harmful in europe. it has been ages since i last saw native ladybeetle. gray squirrel is pretty good at outcompetting our squirrel and what about poor european mink? woods are full of sikas crossbreeding with european deer, there is a big chance your chickens will get eaten by a racoon, coypus are destroying embankments, a tons of trees are not native, like eastern white pine, outcompeting our pines, or black locust, outcompeting just about anything. Prussian carp just about destroyed the population of native crucian carp, ponds are infested with stone moroko and let us not even talk about plant diseases.Dutch elm disease is comparable to chestnut blight.
from my experience living in the US and visiting Canada and also visiting the British Isles… the difference is colonialism and intensive human disturbance associated with such has been around the British isles much longer so it’s less clear what is native and some of the non-native species may have already reached equilibrium with the very human-influenced environment there. Whereas in most of the US and Canada (except some exceptions like the Great Plains) there is much more intact ecosystem left and more invasive species are still actively spreading or could be prevented from spreading there.
I think that plants in Eurasia have a very long history of adapting to heavy grazing and extensive cultivation or dying out before botanists were writing about them. Many evolved methods of coping with the changes – consider crop-following weeds! Or the diversity of plants with spines and thorns in North Africa. The species well adapted to the ways humans disturbed the land in Eurasia were ready to exploit similar disturbances in other continents, when they got access to those areas.
In North America, farming has a long history but it was not nearly as extensive as in Europe by 1492. Perhaps most importantly, Native Americans did not have herds of grazing animals, as in Eurasia (except in the Andes). Some weeds and pest evolved here, but not nearly as many as in the Old World. What a friend calls the “One World Flora” consists mostly of Eurasian plants, at this time.
Some North American plants not considered weeds or tied to disturbance are now spreading in Europe and even changing ecosystem types, e.g. Salal (Gaultheria shallon) and goldenrods (Solidago sp.). The transfer is not all one way, though it is predominantly from Eurasia to the rest of the (temperate zone) world.
The fact that we have a date for the start of the changes does help make them more obvious, too.
I think it’s more subtle than that. Humans as a species don’t act like other known species, we basically choose whether we are going to act as invasives or not. That’s part of the point here. Many of the cultures in the Americas for whatever reason did NOT have as much an impact as those in Europe, sometimes due to lack of access to technology, but other times due to conscious or unconscious cultural choices. In short, not all of them have been equally ‘invasive’ at all times. Writing humans off as ‘invasive’ ignroes the other part where… we don’t HAVE to be, and haven’t always been in every context.
I’m not sure whether humans can be considered an invasive species, aside from the fact that we, as Charlie mentioned, don’t have to be. I mean, our spread has been completely natural (in the sense that it is what any other species does to the best of our abilities. I don’t want to reignite the debate of whether humans can be considered part of nature). Due to our ability to shape the environment we are perhaps the most generalist species of them all.
I am not denying the huge (usually negative) impact we often had on our environment, though.
This is very interesting and I had never thought of that. I’ll look into that a bit. It’s a really good hypothesis, IMO.
