Rising Temperatures Worsen the Negative Effects of Urbanisation

Urbanisation is among the major threats to wildlife. As the human population increases and cities expand, we are invading the habitats of other species. Habitat loss is causing many species to squeeze into narrow ranges, and we are already seeing numerous negative consequences.

Human-induced climate change is also exacerbating the negative impacts of urbanisation on wildlife. The scientific study of a large research team including Prof. Çağan H. Şekercioğlu, founder of the Biodiversity and Conservation Ecology Laboratory at the University of Utah, USA, and Koç University faculty member, and his PhD student, wildlife biologist Dr. Austin Green, has revealed results supporting this phenomenon.

The team set up camera traps at 725 locations in 20 different cities accross North America and analyzed 20,000 days of camera trap data. The images of 37 native terrestrial mammal species, from squirrels to black bears and mule deer, show that urbanisation has a negative impact on both species occupancy and diversity. The phenomenon was most apparent in cities that are warmer and dryer, with less vegetation. Not surprisingly, mammals with larger bodies turned out to be the most affected species.

Results of the study published in Nature Ecology & Evolution suggest that this is at least partly related to the abundance of paved landscapes in urbanised areas, such as concrete buildings and platforms, as well as asphalt roads, acting as heat islands. “The vast majority of animals living in urban areas utilise that night time period specifically to avoid humans, but also to have a bit of a temperature refugia,” said Austin Green, “They stay pretty sedentary during the day, the hottest time of day, and then they use the coolest part, which tends to be at night to actually move around. So if that part of the day is continuously getting hotter and hotter, then they’re not able to get the resources they need.”

Mammals, especially predatory species with larger bodies, are naturally expected to experience habitat loss due to urbanisation. However, the study, which brings together an impressive amount of camera trap data from a large number of locations, is important in terms of examining the impacts of urbanisation under an ecological lens. Prof. Dr. Çağan Şekercioğlu answered our questions about their study.

Did you expect these results? Were there any  results that surprised you?

I partially expected it, but I did not expect such variation between cities –which perfectly points to the importance of conducting large-scale studies, spanning an entire country or an entire continent. Wildlife ecology studies in one city, province or state may not always be applicable to other regions. Therefore, it is critical to carry out larger-scale studies covering a large number of locations. Such studies require the coordinated effort of many scientists and citizen scientists. Camera traps are now widely used in Turkiye, but there is no similarly comprehensive and coordinated camera trap research network. For example, the General Directorate of Nature Conservation and National Parks has hundreds, maybe thousands of camera traps in dozens of provinces, but I don’t even know where all that data is. The right thing to do would be to collect and analyse this data in a central system in Ankara, but I think they are kept in separate places on a provincial basis and used mainly for news stories. Likewise, hundreds of wildlife enthusiasts in Türkiye also use camera traps, but the data from those camera traps are kept separately on their own personal computers. I have collected and analysed more than half a million phototrap data with my students in the forests of Kars Sarıkamış since 2006, but of course this is only one location.

What is the fate of small-bodied mammals, which are generally better at adapting to urban environments, in cities? Do they still have any ecological roles in cities?

We cannot say that all small mammals are able to adapt. Many specialised species are disappearing. But there are those that can feed on the food left by humans and benefit from the decline of natural predators. Their ecological function is much reduced than it is in intact ecosystems. Of course, we cannot generalise these results from the US for Turkiye, because the US does not have millions of stray cats and stray dogs like we do. Therefore, most small mammals and birds have been hunted out. For example, we hardly see squirrels anymore -especially in our big cities.

Did you have the opportunity to compare your study results with similar studies conducted on other taxa? For example, could mammals be more at risk than amphibians, which are generally known as one of the most vulnerable taxa?

I haven’t had the chance to compare yet because camera traps are particularly suitable for mammals, whereas more focused studies are needed for amphibian species. I think amphibians are more endangered because they need humid environments, are more endangered globally, and are more sensitive to drought and climate change. 

Can we say that the same scenario applies to humans as we have a similar physiology to the mammalian species you have studied?

Partly, but of course we humans are able to create the environments we want with the help of our civilisation. Nevertheless, global warming and the heat island effect of concrete-filled cities are also increasingly affecting humans. Unfortunately, many parts of the world are becoming inhabitable due to temperatures exceeding 40°C and sometimes high humidity levels. In some low income countries in the Global South, especially in the tropics, we are expecting millions of extra deaths as a result of this effect -and millions of people have already died due to heat waves. Even humans cannot escape this fate brought by global warming and climate change.

In parallel with your work, are there any practices/solutions that you find appropriate or suggest to reduce the cumulative impact of urbanisation and climate change on wildlife? How should a proper planning look like?

As natural areas are being rapidly destroyed in our country, in the World Environmental Performance Index (EPI) published by Yale University every two years, we are ranked 178th out of 180 countries in terms of biodiversity conservation and protection of natural areas. Many of our protected areas are only protected on paper. The ratio of our national parks to the country’s surface area is around 1%. This should increase to 30% and these areas should be connected to each other through habitat corridors, such as Turkiye’s first wildlife corridor, which I first proposed back in 2008.

The most neglected nature conservation and wildlife concern in Turkiye, which is ignored and could in fact be solved if desired, is stray cats and stray dogs. I estimate that they destroy hundreds of millions, if not billions, of wild animal individuals every year. It is imperative that these animals are sterilised and adopted in a humane way. I have adopted all my dogs from shelters. Feeding and leaving animals on the streets should be strictly forbidden and should be subjected to serious fines. In no other country in the world you see millions of stray animals being fed so unconsciously, rapidly increasing their populations. Because these species are instinctive predators, they continue to hunt even if people feed them. As their numbers increase, green areas, which are already in minute amounts especially in big cities like Istanbul, are becoming death traps, ecological traps for wildlife. This is what I see even in the campus of Koç University. Cats especially hunt birds that come to green spaces like city parks, while dogs prey on mammals such as rabbits, roe deer and squirrels.