For humans, urbanisation has generally been beneficial. Cities are often where people find better access to clean water and sanitation, better housing, employment and opportunities for education – hence extensive rural to urban migration.
For other species, the effects of urbanisation are mixed, and many urban ecologists have characterised species according to how successful they are in cities. This success often hinges on a species’ degree of synanthropy (how much it relies on resources provided by humans, deliberately or not). The biggest ‘losers’, which only use natural resources, are called urban avoiders – they’re usually the first to disappear from cities. The biggest ‘winners’ are called urban exploiters – they tend to be highly synanthropic and most abundant in cities. In between, there are urban adapters – many are edge-habitat specialists and they tend to be moderately synanthropic and most abundant at intermediate levels of urbanisation.
Singapore (SG) had already lost a substantial portion of its original tropical forest habitat (and likely much of its original bat fauna) even before extreme urbanisation further transformed the landscape. But it still has some 20 species of bats. One is Cynopterus brachyotis – the dog-faced fruit bat. And several observations suggest that this bat can probably be called an urban adapter. It’s definitely the most common fruit bat (and maybe the most common of all bats) in SG and it occurs pretty much everywhere along the urbanisation gradient. It roosts in natural foliage and in anthropogenic structures (at least in SG, not elsewhere). And it eats both native plants and introduced ornamentals.
If a species is an urban adapter, then we might reasonably expect it to be resilient to the impacts of urbanisation, no? Well, if we just look at this bat’s ubiquity and ecology, that does seem true. But recently, a group of my colleagues discovered that its genome tells a different story. One of gradually dwindling population size since the 4th century, followed by a sudden and extreme genetic bottleneck and reduction of effective population size around the time of the Anthropocene signal and start of urbanisation in the 1940s. That’s what we see from the composite figure below.