Adaptation of species in response to urban environments

A DW Documentary on YouTube, Nature’s response to urban sprawl has had me thinking since watching it a few days ago. It might be something good to watch while patiently waiting for the servers to reboot!

The reason why it caught my attention was how it discussed the changes to organisms living in city environments and researchers focusing on studying organisms within those environments. One of the criticisms (or perhaps just an enumerated bias in iNat’s data) is that there is a skew toward observations in places where humans live. However, the documentary highlights the incredibly rapid evolution (both behavioural and genetic) which is happening within cities. Here’s a partial excerpt of the documentary’s abstract:

Nature’s response to the spread of cities is astonishing: Why do catfish in the river of a French city systematically prey on urban pigeons on the banks? Why do female birds on a university campus in California suddenly change their mating behavior? How do mice in New York’s Central Park cope with an altered diet of human food waste? How have killifish in the Atlantic built up resistance to deadly chemical waste? And, is it possible for moths to adapt to nighttime light pollution?

New research provides surprising new insights into Darwin’s theory of evolution. Nowhere else do animals and plants adapt so quickly to new living conditions as in cities. Biologists have long known that animals and plants occupy new habitats in the vicinity of humans. But now, new genetic analyses show that these adaptations are accompanied by significant changes in DNA.

Even more surprising: these evolutionary changes have not occurred over periods of millennia, but within just a few decades. The process has amazed scientists, who watch as nature transforms even our most hostile man-made interventions – pollution, light pollution, noise, garbage and dense development – into creative energy for new adaptations. Some researchers believe that our cities may soon develop their own, brand-new life forms.

The documentary made me reconsider whether the skew toward observations in urban environments is really a deficiency in any way. If one were trying to observe adaptation & evolution in those environments it may be the best kind of data.

I’m curious what kind of unique adaptations to city life, whether behavioural or phenotypic, folks here have observed, seen glimpses of, or measured on iNaturalist or perhaps elsewhere. Does iNaturalist data show these adaptations in any way?

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That’s actually kind of a scary thought.

“Rodents of unusual size? I don’t believe they exist.”

In Bremerton, Washington is an important Naval shipyard. Its grounds are almost entirely pavement and industrial buildings; it would seem a hostile place for life. But from an upper floor of one of these buildings, looking down on the flat, tarpaper roofs below, one can see Olympic Gulls nesting. Unlike actual beaches, where humans could disturb them and land-bound predators could plunder their nests, they are secure on their tarpaper “beach.”

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This reminds me of some discussions I’ve heard about other species using us as literal “human shields”. There have been a few studies that point to female bears raising cubs closer to humans as a means to avoid infanticide by male bears:

But male bears are often leery of getting too close to human civilizations, which may provide the females an opportunity. Leclerc and his coauthors looked at extreme cases from 2005-2012 in which all of a bear’s cubs survived, or all of them were killed, since males intent on guerrilla family-forming will usually wipe out the whole litter if they can.

GPS data and spot-checking from the ground and helicopters to see whether cubs had survived the mating season showed that the most successful mothers were the ones that hung out more often relatively closer to humans, while those that often avoided human infrastructure were the ones that lost cubs.

J.R. Learn, Mama Bears Use Humans To Keep Their Cubs Safe, Smithsonian Magazine, 2016-06-27

Apparently they also manage to put on more mass when in proximity to humans. Yet there’s also really high mortality for bears living near humans.

I’ve read some speculation that a similar process is happening with deer, although I haven’t seen research on whether this is a new adaptation. But it seems that does are frequently using backyards as “daycare centres” to leave their fawns while they go off to forage. I’ve seen it a few times myself, in addition to adult deer frequently using backyards in my neighbourhood to sleep, despite there being more secluded ravines nearby. It may affect a deer’s risk perception, but perhaps that’s just a side-effect.

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Clearly, you’ve never been to Singapore. :pirate_flag:

In all seriousness, though, I’ve seen some interesting genetic adaptations to selection pressure. I grew up in Louisville, KY; since my mom and dad were still undergrads, I spent a whole lot of time on the UofL campus. There is a fairly robust population of squirrels on campus, and notably a high incidence of albinism among said squirrels. (There’s always a few melanistic ones as well, but leucistic and true albino seem to be better represented, at least to the best of my recollection.)

Things that I noticed as a kid were that 1) a white-furred squirrel was far more likely to get treats than a standard gray, and 2) white, black, or gray-furred squirrels with faces and bodies even slightly more neotenous than average would get treats before a more normal looking squirrel of any color. If the squirrel was white-furred, baby-faced, and plush-bodied, it had hit the jackpot. One of these days, I expect a good chunk of the campus population of Sciurus carolinensis to look like little anime characters.

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It’s an interesting question, and has actually been puzzling people for a bit longer than the making of the documentary! Recently a paper in Nature has shed some light on something that was noticed in the UK back during the beginning of the Industrial Revolution.
It’s a classic example given in a lot of Evolutionary Biology classes about animals adapting to humans. Here is the very, very short version of the story:
Back during the early 1800’s there was a species of moth called the “Peppered Moth”. It is normally white in color. When factories started belching out soot and other pollutants and began darkening surfaces a crazy change happened: the Peppered Moth began to develop a black form, and it became more and more prevalent until it was the dominant form. The black color let it blend in with the sooty trees where it rested during the day.
This team apparently found the exact gene that triggers this mutation. Just one. And the change in gene expression was found to have occurred around 1819, right about when things started getting polluted. Apparently the gene also works to help with mimicry in some of the tropical butterflies that are toxic too. It truly is case of human activity inducing a genetic change that increases fitness and then passed down.

https://www.bbc.com/news/science-environment-36424768

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Well, even as someone who studies adaptation to urbanization, I would disagree with this statement:

I don’t think that’s supported by research, and have a hard time imagining a line of evidence that could support that statement (for any environment really). But that’s probably just typical pop sci writing hype.

I do think that iNaturalist data has an important role to play here, especially as many natural history collections are biased towards non-urban areas - scientists primarily collect from very natural areas. So while complementary geographically, the issue is that these two datasets (NHCs and iNat) are collected/created via two very different processes, so analysis and interpretation is difficult and limited in some ways. A big one is that data from iNat observations is often quite limited in comparison to the data collectable from an actual, physical specimen - we usually can’t get precise measurements, no genetic information, can’t examine internal components, etc. from iNat data.

A good example of a study that leverages iNat data to study urban adaptation is this one: https://www.nature.com/articles/s41598-022-05746-2

It shows strong evidence for parallel adaptation of coat color in squirrels from natural/rural to urban areas. It leverages the fact that there’s a known genetic basis for coat color to infer that the pattern observed in iNaturalist data is genetically based and truly represents adaptation. This is pretty strong evidence, though even stronger would be sequencing for the basis of coat color traits from observed squirrel specimens across the gradient to confirm the genetic basis.

So I think this study indicates a real strength of iNat data (high number of samples across multiple urban areas that would have been nearly impossible for scientists to collect due to logistical reasons) and also shows how iNat data often needs to be combined with other lines of evidence (genetic mechanisms in this case) to really make strong inferences about adaptation to urban environments.

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Now I recently did some work on a species of exotic parrot down in southern Florida called the Mitred Parakeet. I was looking to discovered why they were thriving so well when other exotics couldn’t establish themselves.
While a lot of the parrots down in Florida are cavity nesters, in parts of the Mitred Parakeet range they actually nest on cliffs and small depression within them instead of trees. The species that nest in cavities suffer from multiple issues; competition from other species, including native ones, lack of suitable trees, and development that can wipe out large areas where they may have been living. Basically they have a constraint on resources.
Mitred Parakeets on the other hand were suddenly living in a giant, never-ending expanse of cliff-like places to nest; buildings. From what I had gathered they had benefited from what is called synanthropy. This is where they actually benefit from living near humans. Similar to the advantages of Eurasian Collared-Doves. With abundant nesting sites and what is basically a continuous range of expansion from Miami to north of West Palm Beach, they were easily able to adapt and quickly increase their population.

So while this is not a genetic change, it’s a case of a behavior adaptation/taking advantage of the situation to make a species thrive in a brand new environment.

Cities are basically a sieve for nature. You adapt very quickly or you die. Change your behavior or have a change in genetics, but by the very nature of a city it has to happen fast. That’s why you would see bias I think. There aren’t many places on Earth where I can think that there is so much pressure to adapt quickly.

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I have read a couple of books on how wildlife is adapting to suburban and urban places:

“Welcome to Subirdia” by John Marzluff and " Urban Raptors" by Clint W. Boal and Cheryl R. Dykstra.

The first book covers more than just birds.

I have seen how some birds have adapted myself. Gulls in Cleveland, Ohio follow the huge ore-carrying boats up the Cuyahoga River in winter (before it freezes). The big boats chop up fish or just stun them. It is easy food for the gulls that have learned this behavior. As a birder, I have gone to the parks on the lakefront or along the river to scan the huge cloud of gulls behind the ships for rarities.

There are also warehouses where the gulls nest using the flat roofs. It’s sort of like a wide open beach, I guess. And, not many people go up there.

A number of birds have also adapted to the introduced ornament fruit trees planted by people. American robins especially enjoy the fruit and can be seen in large flocks where these trees are planted around shopping areas.

I’m sure people have heard about the peregrine falcons that nest on buildings. But, they also nest on large highway bridges.

One change hawk researchers here in Ohio have seen recently that is unusual is red-shouldered hawks nesting on bridges. I have seen this myself. A big branch in a big sycamore tree that hawks used for years fell down. (Just the branch. Not the whole tree.) So, the hawks used a bridge close by the past few years instead of using another branch/fork in the tree. The nest is getting pretty big as they add new branches every spring. The nest isn’t affected by the weather over the year because it is under the bridge roadway. This species of hawks wasn’t know for using man-made structures. They have nested successfully in urban/suburban areas for years. They are tolerant of people.

Species that use meadows are really being hurt. An open space usually means that something will be developed on it quickly. Only parks/preserves will keep those species alive. At least it seems like some people are realizing the value of wetlands. Some cities are changing large grassy drainage ponds. They are planting small water-tolerant trees and plants because the plants soak up and hold more water in a deluge than just a big open area. I have seen that myself in some local communities. Some people are upset because it takes away a fishing spot. But, I think, in the long run, they will enjoy the parks with more plants. And, these new areas attract birds. Most people enjoy birds even if they can’t identify them. And, there are plenty of places to go to fishing in Northeast Ohio for the unhappy people.

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Maybe species would be far more plausible. As regards, there are already species that are endemic to a certain city, for example Hieracium australe subsp. australe in Milan. But you it is not so easy to know if it has always been there without extending its area or it ended up being restricted to that city.
There is the potentiality for the appearance of brand new species, especially in the case of genera characterized by fast speciation after hybridization (e.g. Oenothera subsect Oenothera.

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Canada geese also use people as human shields. In many areas they have learned that counterintuitively they are safer from human predation closer to cities even though there are more people. I’ve noticed similar behaviour in mallard ducks as well.

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Just a quick note on terminology that may help answer OP’s original question. Many people, including scientists, often use the term “adaptation” quite broadly to mean any response by an organism to a change in its environment that helps the organism. “Adaptation” in a stricter sense describes the process of evolutionary change, which OP asked specifically about. Evolutionary responses are rooted in heritable changes, and most scientists would agree that these changes will include a genetic basis (though some might think of an extended evolutionary synthesis).

There are many examples of organisms adapting (in the broad sense) to urban environments, often via changes in behavior. However, many of these examples will be examples of behavioral plasticity, or the ability of an individual organism to conduct multiple different behaviors dependent on context, sometimes (but not always) because of learning. This type of plasticity is one of the quickest ways for organisms to respond to changes in their environments, but it often isn’t evolutionary. In fact, conclusively demonstrating that these changes are evolutionary responses (ie, rooted in genetic changes) is often quite difficult, even in circumstances where we might have good reason to suspect that they are.

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I watched parts of the documentary. I’d think those French catfishes are examples of adaptation but not genetically changed. Scientists are always trying to prove Darwin was wrong, which is what science is. I mean it is permissible. For genetic changes to occur, there must be reproduction, and the offsprings must be selected upon by natural selection. For a fish known to live 50years, the size it is able to eat pigeons may be like lets say 3 years of age, fishes released in 1980s, there is probably not a lot of generations compared to moths which can have several generations per year. However, populations may be isolated , and genetic deviations can occur after some time. As an avid fisher, I’ve known of how aggressive catfish can be, even though some species are perceived to be bottom feeding. Some species can take topwater lures. It is not unusual for fishers to use a lure that looks like ducks and mice in some parts of the world. I don’t use those but I’ve caught a few on poppers. In asia, one big species is Wallagonia leerii. I haven’t got the chance to land one , maybe one day. It is known for eating tortoises and even monkeys. and there are the several giant catfishes from Amazon rivers. These catfish will all learn to take a water bird if the opportunity exist for a success ambush.
The only examples of clearly evolving species under urban environments are guinea pigs, cat, dogs, feral pigeons, numerous cultivated plants…Even humans are evolving to fit urban cities and climate but there is less of an isolation factor as today’s world is about globalization. These creatures such as guinea pigs are selected over a long time, but it is combination of factors, like chance, human selection, that cause traits that are clearly visible. There are genetic changes that human eye can’t see on the surface, such as some semi-dominant traits which sometimes appears sometimes don’t.
Why is evolution a long process or happens very fast ? This is probably depending on how people look at it. The “species” is defined by human beings. It is a classification system. In reality, there exist populations which are slightly different but still about the same, so we put them in the same group. Yes, every group of species are probably evolving. The mechanism of slow evolution is the huge number of the same species may dampen its speed of change. The moment a group deviate too much, we put them under another name. This could be a very long time. In my opinion, they didn’t find anything that show fast evolution, as when that isolation is broken, the species will be in feedback loop. This is under the influence of earth’s longer term trends like a warming world or cooling world.

No, no that wasn’t at all what I “specifically asked about”. I very specifically asked, about “what kind of unique adaptations to city life, whether behavioural or phenotypic, folks here have observed”? That was intended the broad sense, much like it was presented in the documentary. I suspect that you’re responding to the title of my post (about as meaningful as a title in a legislative document), rather than the text contained within. I’ll fix the title.

I’m sufficiently familiar with iNat data to know that, aside from a few genetic barcodes, it doesn’t directly include genetic data. Hence why I ask about the much broader categories of behavioural and phenotypic changes. Not all behavioural adaptations are connected to a genetic change. That’s also touched on by the excerpt from the documentary’s description: Scientists are finding that some of “the adaptations are accompanied by significant changes in DNA”.

So I am also curious what other adaptations iNat participants have observed, even if it appears to be purely behavioural. Part of that is we usually can’t tell. I’ve heard Park Rangers suggest raccoons and bears have become less aggressive than they used to in the past. Maybe there’s been a really strong selective pressure that’s resulted in less “aggression hormones” in these species. Or perhaps it’s a learned behaviour.

Similarly, others including don’t need to point out the obvious, e.g. “I’d think those French catfishes are examples of adaptation but not genetically changed […]”; if you watch the documentary in full, you’ll note that it does not claim that, nor did I. The documentary’s description on YouTube probably wasn’t written by the same person who created the documentary and I just included it as a hint of why it might be worth watching.

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Globally, urban area is projected to triple until 2030, mostly in regions identified as “biodiversity hotspots,” with profound effects on ecological processes, including habitat destruction and soil/air/water pollution. This study finds that flora/fauna become more similar over time, and that these reductions in biodiversity decrease the capacity of ecosystems to capture essential resources and maintain ecological processes. Reductions in urban biodiversity have consequences for human well-being, reducing the benefits people can obtain from nature. This research provides planning recommendations for protecting urban biodiversity based on ecological knowledge: https://www.sesync.org/research/urban-biodiversity-ecosystem-services

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The reason they are biodiversity hotspots is, quite simply, because they are the places where urban expansion has not already happened. What we call “biodiversity hotspots” are the baseline data for world biodiversity before there were cities.

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