The Urban Jungle

One prediction is that by about mid-Century, over three-quarters of the human population - that’s destined to reach 10 billion by then - will live in a city. And cities themselves will of course need to grow to accommodate this burgeoning populace. Where they’ll expand into will inevitably be the habitats of wild animals - with what effect? Speaking with Chris Smith, Arielle Parsons has been trying to answer this question in the US...

Arielle - The idea is that these cities are out of ecological balance: that humans have taken away too much of the natural habitat and too much of kind of the natural systems and so they're not really functioning to the same level as we would expect of wild ecosystems. And so we wanted to look at that in terms of the mammal communities and compare two cities in the United States - Raleigh North Carolina and Washington D.C. - to nearby wild areas and see if we could see any differences in terms of diversity - so the number of animals present - and then the relative abundance - so kind of the population sizes or some estimate of the population sizes of each species.

Chris - Sounds like a very tall order! How did you do it?

Arielle - It is indeed a tall order! And so we had to cover these really large areas in both cities to get kind of an idea of these communities in the very suburban areas, all the way out to the more wild areas. And so to do that we used citizen scientists to run camera traps - devices that we can put out in the forest, or in a yard - and when an animal walks by it senses the body heat and the movement and it automatically takes a series of pictures. Without these volunteer citizen scientists we simply couldn't have covered the areas that were necessary for this study.

Chris - Where were they deploying their cameras?

Arielle - So we asked them to deploy them in different areas around these cities that were based on housing density so areas of highest housing density, or what we call suburban areas. And then, as we step down in housing density, we get to these wild areas. Citizen scientists then put those cameras in yards and also in forested areas - both small forest fragments less than a square kilometre, and large forest fragments. 

Chris - And how do you log all the data?

Arielle - We use a software called eMammal: a network that helps camera trappers organise their data; and that software allows our volunteers to go through all the pictures that they collect and identify the species in them. Then they upload the data to us so that we can look at it and make sure that they've correctly identified species. There are some some tricky ones here.

Chris - Why?

Arielle - Why are they tricky?

Chris - Yeah!

Arielle - Yeah. So we have two fox species: we have the red fox. Then we've also have the grey fox, and they're of similar size and, especially at night, these cameras - they're black and white - it's an infrared flash - so we can't see whether the coat is red or black. And so there are some characteristics, especially of the tail, that make it easy to distinguish. But our volunteers sometimes have trouble...

Chris - Assuming that your volunteers were diligent and they weren't too easily confused, what did you find?

Arielle - So we found, rather surprisingly, that the diversity - so the number of species that we were getting on our cameras - was not significantly different between the suburban areas and the wild areas. And, in fact, in Raleigh the diversity was significantly higher in the suburban areas compared to the wild areas. We did have some exceptions: for example, we only found beaver in the suburban areas and we never actually detected it in the wild areas; and we never got bears in the suburban areas!

Chris - I guess that's a bit of a relief in some respects isn't it!?

Arielle - I think it is at the same time we know that bears actually can do quite well in suburban areas. The tricky thing is making sure they stay wild. So especially not letting them get into trashcans and allowing them to maintain their distance even if they're living close to us.

Chris - Does one take away from this then that, contrary to the prevailing view that these urban environments are really bad for wildlife, in fact the opposite is true?

Arielle - Yeah, I think in terms of these mammals - and it is important to say that these mammals that we were sampling with our cameras are mammals that are chipmunk-sized and up, so there are a number of mammal species that this wouldn't apply to - but certainly in these two cities it seems as if this idea of ecological function being different between suburban and wild areas, at least as it applies to the mammalian community, is maybe not the case but there have been a number of studies on other taxa showing that urban areas and suburban areas do have quite drastic negative effects and so we want to be very cautious about extending this, you know, to other taxa in other cities even.

Chris - So what about other cities? Because, obviously, you've looked at just two; you looked at a lot of animals in a big area admittedly, but it is just two zones isn't it? So what would happen do you think if you went elsewhere, both in the US and maybe even further worldwide.

Arielle - Yeah. And that's something that we're very very interested in doing. We're really interested in looking at cities that have an impact apex predator. In the east, in these cities, of course there were once mountain lions and wolves - they are here no longer. But there are cities in the United States where the foxes the raccoons et cetera still persist in the presence of an apex predator like a mountain lion or a wolf. And we would expect then perhaps the dynamics to be a little bit different. And then the other thing, kind of thinking about cities around the world, of course cities in different parts of the world - and Europe for example - tend to be more concentrated less sprawling. The separation between urban and suburban and wild tends to be very stark. Whereas here there's quite a lot of sprawl. And so we would then expect it to be more difficult for animals to go in those small concentrated European cities from the wild straight into the suburban areas. But it's something that we're very interested in and looking into further, and we actually have some partners in Germany right now that are just beginning a replication of this study.