Welcome to synurbia
Some animals are synurbic, and some aren’t.
It is, by definition, impossible for a whale to be synurbic, but perhaps not a frog.
What on earth am I going on about?
I’m talking about those animals and plants that like living where we do.
But the concept of synurbic species, and the process of synurbization, is being taken increasingly seriously by scientists, as too is the whole concept of urban ecology.
Because they address the intriguing question of whether wildlife is finding ways to live alongside people, and our urban sprawl.
More intriguingly, they also examine whether some species are going further: and are positively adapting to life in towns and cities, becoming more successful as they do.
That could lead to the rise of synurbia – where wildlife comes in from the country, and learns to live all around us. That’s interesting in itself. But it is something we can all look out for. Are animals and plants encroaching on your back yard? Are you increasingly living in synurbia?
To add another definition into the mix: some species are synanthropes. These are those species particularly associated with humans and places of human habitation
(The prefix “syn” comes from the Ancient Greek for “together with”.)
I’ve taken the definition above from a new research paper published by Robert Francis and Michael Chadwick, both of whom study at King College London, UK.
Published in the journal Applied Geography, the paper details Francis and Chadwick’s thoughts about the concept of synurbic species. I want to share their thoughts with you – but also as a way to ask you to think about the concept of synurbia.
Examples of synanthropes include tapeworms and lice, agricultural weeds and pest species, as well as pigeons and rats (ecologists exclude domestic species from this discussion).
These species do well around people, living off us, our crop fields or waste. Some, say Francis and Chadwick, have thrived, as humans have expanded their reach around the world.
However, many of these species also do well in other ecosystems; in the wild and in rural areas not yet urbanised.
Synurbic species however, go a step further. They should be defined as species which live at greater densities in urban areas than rural ones, say Francis and Chadwick.
And to understand them better, the researchers say, we need objective measures of how many individuals of a species are living in towns and cities as compared to the country.
Recent studies have shown that blackbirds, wood pigeons and mockingbirds among other birds, badgers, some insects and plants all live at greater densities in many towns than outside of them.
This week, entomologists announced a study into whether UK cities are becoming a haven for insect pollinators.
Most interestingly, Francis and Chadwick also spell out in their paper how some species can become synurbic. Understanding that will help ecologists understand how human impacts affect wildlife, and which species have an opportunity to adapt to city-living. It will also allow researchers to deal with a less-regarded category of synurbic species – pests, such as rats.
Much of the work done so far has focused on birds: some species, such as light-vented bulbuls have learnt to make nests out of man-made materials; others such as monk parakeets have adapted to nest in telegraph poles. Birds have changed their egg laying habits, songs and even escape flights, with the northern mockingbird learning how to recognise individual people, and flee from them differently.
Fewer studies have been done on mammals, though eastern grey squirrels and northern racoons have responded well to urban environments, while stone martens often prefer to den in buildings than more natural sites.
Foxes now live in densities up to 30 times greater in urban areas than in the country, as shown by studies in Zurich, Switzerland and Bristol, London.
As for invertebrates, numbers of dust mites and bed bugs are likely much higher in urban environments, though surprisingly few studies have been done to show this. Invasive mosquitoes have taken to city life, reproducing in bird baths, guttering and disused tyres, say Francis and Chadwick, as have sandflies. Bumblebees change the way they forage in towns and cities.
But it may be plants that have best embraced synurbization. Walls make great habitat for cliff-dwelling species and several plant species in the UK, including ferns such as maidenhair spleenwort, are more abundant on urban walls than in their original cliff habitat.
Other plants respond to urban habitats by hybridising – creating new types such as the Railway yard-knotweed, which is a hybrid of Japanese knotweed (Fallopia japonica) and the Chinese fleecevine (Fallopia baldschuanica), which is mostly found in London.
Whether these species are actually adapting, in evolutionary terms, to urban life is harder to show.
Some are certainly making behavioural changes; town-living European foxes have reduced territories, forage in packs, eat our leftovers and tolerate people far more.
But that doesn’t mean their “evolutionary fitness” is increasing. Foxes may naturally have a range of territory sizes, for example, and may simply use smaller territories more in towns, and larger ones in the country. They do as needs must, rather than urban foxes on the whole are evolving to have permanently smaller territories.
There is however, tantalising evidence that some species are evolving to live around us.
Urban house finches have evolved different bill shapes and bite with different forces to their rural cousins, so they can eat different seeds found in towns, studies have shown. Blowflies in towns and the country have different life histories – and these seem to persist down the generations in flies reared in the lab – suggesting the urban flies are evolving away from their country cousins.
Separating out genuine adaptation from more plastic responses will need some strict comparative studies to be done. But done they should be, as the difference is important.
If species can only adapt to city life in the short term, the future for them is bleak as global urban sprawl continues, eating into more of the wilderness. But if they can quickly evolve to exploit this new environment, we may all one day be living in Synurbia.
If you think it’s happening already, let me know.