Rivers of ink have already flown in the many attempts of philosophers, ecologists, and conservationists to define nature and the natural, so I will refrain from releasing my own tributary. But let it be clear that I consider human cities as a fully natural phenomenon, on a par with the mega-structures that other ecosystem engineers build for their societies—the only difference being that whereas ants, termites, corals, and beavers have been maintaining their roles at a stably modest level for millions of years, the scale of human ecosystem engineering has grown by several orders of magnitude over just a few thousand years. Whether, as a species, we are suited for living in such dense, complex communities is another matter, and I will come back to that at the end of the book. But first, let us examine the modern, human megacity for what it is: an exciting, novel ecological phenomenon.
In the beginning, at a time when our species had just emerged from its smaller-brained predecessors, and was still so rare that it would have qualified as vulnerable by today’s Red List standards, we were already small-time ecosystem engineers. Not unlike beavers, our hunter-gatherer ancestors would find a suitable spot, preferably with natural shelter—a rocky overhang or a cave, perhaps—and settle there for a while to exploit the environment before moving on. Some “proto-domestic” animals like the ancestors of dogs may have followed in our wake and hung around camp to scavenge refuse, and we may even have brought our own domesticated animals and plants: edible rodents in cages (like the Polynesian rats carried around by the Lapita people) or cuttings of medicinal plants. Settling would involve burning or clearing the vegetation around the camp, tending edible and medicinal plants and weeding away the undesired ones. We would create fireplaces to cook the fish and game we would hunt, as well as the clams and snails we would collect from the stream. We would raid bees’ nests to get honeycombs and the protein-rich bee brood, hunt the local megafauna, and collect fruits and nuts from the forest. Like beavers, we may even dam a creek, in our case to collect the fishes that would then be splattering about in the shallow waters downstream. Our effects on the environment would be subtle—a drier microclimate due to clearing of the vegetation, a local depletion of large animals, the introduction of a few alien species—and the environment would quickly recover whenever a group would pack up and leave for new hunting grounds.
Much of this changed when we took up farming. The revolutionary invention of growing food, rather than searching for it, had two important consequences for our way of living. First, growing crops for subsistence around a settlement meant that it was no longer necessary or profitable to live the nomad life. After all, going to the trouble of setting up fields and planting them clearly was a long-term investment. Until the soil became exhausted, it was best to stay put. Secondly, it meant that our trophic level changed—trophic level being an organism’s position in the food pyramid. Green plants that use the sun’s energy and “eat” carbon from the air sit in trophic level 1 as the world’s chief “primary producers.” Level 2 is occupied by vegetarian animals that consume those primary producers. The third level of the food pyramid is where we find the predators that eat those plant-eaters, and so on. The food pyramid is pyramid-shaped because only one-tenth or so of the energy produced by one layer is carried upward into the next layer. The rest is lost along the way as waste, heat, and power to run the bodies of the organisms in that next layer. And since energy translates into how much life a level can support, in any habitat you’ll find ton of green stuff (level 1), millions of plant-eating insects (level 2), thousands of insectivorous birds (level 3), a bunch of weasels and hawks (level 4), and perhaps just a single top-predator, like a lone tiger or a solitary eagle, at level 5. Humans, by changing from chiefly hunting to mostly farming, collectively stepped down one tier in the trophic pyramid—where there was much more energy and therefore much more space to grow.
And grow we did. Five or six thousand years ago, we improved irrigation and soil tilling to such a level that frequent relocation because of depleted soil nutrients was no longer necessary. Agriculture proved such a success that not everybody in a village needed to be involved with it. It was left to specialists while the rest of the settlement could take up other necessary trades. This meant that these permanent settlements became places that could supply food and coveted goods to their hinterland. This in turn led to the development of transportation technologies, and people skilled at building and maintaining these. Cities also became the places from which organized warfare emanated, subjugating tribes that still adhered to hunting and gathering, and thus further spreading the agricultural, village-building lifestyle. Around that time, roughly 6,000 years ago in Mesopotamia, the first true cities appeared. One by one at first, but as the centuries went by, more and more parts of the world began to show signs of urbanization, with new cities popping up in India and Egypt, then in more rapid succession: Pakistan, Greece, China … An animation based on the research by Meredith Reba and her colleagues at Yale University shows how cities appear all over the planet, from 5,700 years ago until today—slowly at first, but then, like corn popping in a pan, building up to the deafening crescendo of urbanization during the past century.
Over the next few decades, the popping is only expected to become louder, with megacities (10 million inhabitants or more) setting the stage. In the Pearl River Delta, one of China’s main economic hubs, so many cities are now squeezed together in an area smaller than the unimpressive size of Belgium, that it is termed a “megalopolis” with a combined population of 120 million, almost the same as all of Russia. By 2030, almost 10 percent of all people on earth will live in only 41 megacities, and most of those will be in Eastern China, India, and West Africa. Kinshasa, still a quiet backwater a few decades ago, will hold 20 million people, and in Lagos the population will be more than 24 million. Those figures may be mind-boggling, yet the strongest urbanization, relatively speaking, will actually take place in the small and medium-sized cities (that’s anything below 5 million inhabitants) in formerly rural countries. Such cities are expanding rapidly, by over 2 percent a year, while the annual growth rates of the really big megacities is just 0.5 percent. Over the next decade, the developing world’s smaller cities are going to absorb twice as many people as their bigger brothers. Between 2000 and 2010, the urban population of a country like Laos, for example, which lacks really large urban centers, has doubled.
All these statistics are not to say that experts agree over what a city really is. The socio-economic definitions vary from period to period and from place to place. In Norway, a settlement with 200 inhabitants is already considered urban, while in Japan you need 50,000 for the same status. City status may also be an administrative thing. Some cities are “official” and therefore can claim certain benefits from the state. For example, only two of the twelve London boroughs are official cities, while none of the others, nor London as a whole, is legally entitled to call itself a city. Not to complicate matters, I’ll take a pragmatic approach and simply consider cities as those areas where the density of humans and their buildings are distinctly increased and with it, the infrastructure and average income. But those are only the human factors. In their wake come interesting ecological characteristics.
3
DOWNTOWN ECOLOGY
“Pang!” Sow-Yan uses both hands, one pulling an invisible trigger, the other holding an imaginary barrel aimed at the blazing mid-day Singaporean sky, to imitate a rifle shot. Again he goes, “pang!!.” The impersonation comes in reply to my question about the Indian house crow situation. “In my area, they shoot them down,” he elaborates with some indignation. “For no reason! Just someone complains about them, and that’s it. Also, everybody is using the wheelie-bin now, so the crows cannot get to the garbage anymore. Last time, they would just tear open all the refuse bags.”
We are hiking along Singapore’s south coast. My host, Chan Sow-Yan, a retired computer engineer, naturalist, and local mollusc expert, has paused for a second to do his crow-culling demonstration and then
paces on, toward the place where the Rochor Canal joins the Kallang River. Here, a promontory juts into the waters, and he takes me up there to overlook the estuary. The group of house crows (Corvus spendens) has flown off, but their place is immediately taken by an excited bunch of Javan mynahs (Acridotheres javanicus), beautiful anthracite-and-white birds with mischievous eyes, bright yellow legs and a ditto beak adorned with a small crest of tufty black feathers. The mynahs begin running about, picking up edible morsels from among the cow grass (Axonopus compressus) and touch-me-not (Mimosa pudica). Sow-Yan points at the water’s edge, where the cow grass gives way to yellow-flowered water mimosa (Neptunia oleracea). Then, pointing left and right, he draws my attention to the clumps of pink eggs of the Pomacea apple snail clinging to the shore, the massive peacock bass (Cichla orinocensis) coming up for air, and a tiny red-eared slider turtle (Trachemys scripta elegans) quietly paddling along just beneath the water surface.
Kallang Riverside Park is a rich tropical ecosystem. But that does not mean it is a wild, idyllic paradise. Instead, it’s a tiny pocket of greenery tucked in between Singapore’s high-rise buildings. A few lawns with clumps of mango, coconut, and fig trees; Malay girls taking selfies on benches, and winding paths where European joggers brush shoulders with Indian youths on skateboards; a helmeted elderly Chinese lady on a bicycle with three coconuts in the front basket. The promontory where Sow-Yan and I stand, and the embankments with the patches of pink snail caviar, are made of unforgiving concrete. The river is no longer tidal because of the gigantic Marina Barrage downstream. The mynahs and crows are eating from discarded coconut shells and other leftovers from people’s picnics, and the carpet of freshwater algae that the turtles and water snails forage on grows over bricks and plastic bottles. Due to flooding or leaks of the city’s sewage system, the water itself carries the unmistakeable chemical signature of the 5.7 million inhabitants of Singapore. A study led by Xu Yonglan of Singapore’s Nanyang Technical University found 0.1 milligram of pharmaceuticals per liter of Kallang River water (mostly painkillers like ibuprofen and naproxen); similar amounts of estrogens (from cosmetics and pharmaceuticals) and an insecticide that is used to kill fleas and ticks on pets. In other parts of Singapore, the researchers found up to 1.2 milligrams of caffeine (about as much as in a teaspoonful of coffee) in every liter of river water.
Moreover, each and every one of the animals and plants that Sow-Yan and I spot are not native to Singapore. The house crow, originally from India, Sri Lanka, Myanmar, and Yunnan, suddenly appeared in the port in 1948. Nobody is sure where they came from. Perhaps plantation-hopping from Malaysia where they had been released half a century earlier to control a caterpillar infestation in coffee groves. Or maybe as stowaways on ships. Either way, the crows fared well, increasing from several hundreds in the 1960s, to hundreds of thousands by the beginning of the twenty-first century. Despite the culling of at least 300,000 crows over the past fifteen years, and a slew of measures to discourage them from foraging in refuse and nesting in the omnipresent yellow flame trees along Singapore’s streets, the crows remain a common sight (and, according to Sow-Yan’s neighbors, a nuisance) all over the city. The Javan mynahs arrived as pets (they are sought-after cage-birds, and virtuoso impersonators) around 1925, from Java or Bali, where they occur naturally. In the 1960s, ornithologist Peter Ward still wrote of them, “A shy bird which visits gardens in the suburbs, but which is only occasionally seen in the city.” Since then, they clearly have thrown all shyness to the wind and have become the city’s most numerous and noisiest bird species, probably rivaling the human population in terms of numbers. “The chairs in the coffee shops are full of their shit,” Sow-Yan says ruefully.
The ubiquitous cow grass, a tough broad-leaved grass that is underneath almost every footstep you take in Southeast Asia, is originally from Central and South America, and the same applies to its companion, the ever-entertaining touch-me-not, with its leaves which wrap up instantly when you touch them. Their sticky seeds have been hitch-hiking their way across the globe for centuries via clothes, shoe soles, and the wheels of vehicles. And nobody is really sure where the water mimosa is from, but it’s certainly not native—probably an introduction from Mexico, Sow-Yan thinks.
The huge apple snails that we see slowly sliding along the sheets of plastic at the bottom of the canal, their tentacles bristling, originally hail from South America. They began their global maraud probably via dumped aquarium water and are now proud members of the snail contingent on the list of the world’s most feared invasive alien species. Also on that list, and another escapee from the aquarium trade, is the red-eared slider, again a species originally from tropical America, while the peacock bass, who can call the Amazon river its home, has settled in the city state thanks to “overenthusiastic angling fans,” according to Singaporean fish experts Ng Heok Hee and Tan Heok Hui.
The urban ecosystem of Singapore, like that of cities all over the world, no longer consists of a selection of local, native species. Instead, in tune with its human population, it has been assembled from immigrants from all over the globe. Either intentionally or accidentally, people have been ferrying flora and fauna across the world for as long as they have been trading and traveling. Places where human activity reaches fever pitch—places like Singapore, the world’s second-largest port—abound with such exotic species. These urban ecosystems are formed not by ages of evolution or the slow colonization by species under their own steam and of their own choice, but by human diligence alone. Many cities’ ecosystems run completely on non-native species, especially under water. The marine environment in San Francisco Bay, for example, is dominated by sea creatures from elsewhere. Most of these have probably hitched rides in ballast water—the seawater (including everything that lives in it) that ships pump into their hulls to improve balance after unloading their cargo, and which they then dump in their next port-of-call.
Sow-Yan observes the beads of sweat that have begun to form on my brow. “Thirsty? Shall we have a drink?” He leads me across Crawford Street into a maze of tall apartment buildings. We stop in a small square, planted with cow grass and a few ornamental palm trees inside a towering chimney composed of multiple blocks of flats, their hundreds of growling air-conditioning units billowing out a constant stream of hot air. We sit down at an open-air food court and watch the Javan mynahs forage for scraps of food among the legs of the plastic tables, their beaks slightly ajar in an attempt to cool off. They, too, are feeling the effect of the urban heat island.
First described by geographer Tony Chandler in his 1965 book The Climate of London, the “urban heat island” is the result of several things. To begin with, the activities of millions of people, packed together in a small area with all their cars, trains, and other machines, creates a lot of excess heat, which remains trapped among the tall buildings. Secondly, the stone, asphalt, and metal of streets, pavements, and buildings absorb heat during the day, either directly from the sun or via reflections off windows, and at night only slowly cool off, radiating out heat all the time. The bigger the city, the larger the heat island; every tenfold increase in number of inhabitants raises the temperature by about three degrees centigrade. In the world’s largest cities, it can be more than twelve degrees hotter than in the surrounding countryside. Furthermore the column of hot air that slowly rises from the city center provokes a city-directed breeze from all directions. As it rises, the air column cools down and water begins to condense around particles of city dust contained within it, resulting in a phenomenon called urban rain. In other words, some cities are so large that they produce their own climate: the wind is always blowing toward them, and it’s distinctly hotter and wetter there than in the surrounding rural areas.
In Singapore, the urban heat island has its epicenter exactly where Sow-Yan and I are sweating over our sugar cane juice. According to measurements by the National University of Singapore, we may add seven degrees Celsius to the already balmy tropical temperature. It’s time to get i
nto Sow-Yan’s air-conditioned Toyota and head for the Marina Barrage.
To get there, we have to travel some four miles around the Downtown Core, the futuristic heart of Singapore, where massive feats of modern architecture are bathed by ten-lane expressways, like boulders in a stream. From the car, I glimpse forgotten bits of vegetation between the buildings that remind me that urban ecology is an ecology of fragmentation. Much of the city consists of concrete or steel, surfaces that can only support rock-perching birds like swifts and peregrine falcons, and minuscule life forms that create a film-like ecosystem on the weathering surface (bacteria, lichens, algae—and some tiny animals such as silverfish and springtails that can eke out a living in this two-dimensional habitat). Most other life forms cannot live on the city’s impervious surfaces, but need some sort of soil. Mind you, “soil” may be as simple as those cracks in the pavement where the airborne spores of a Pteris multifida fern germinate. Or the edge of a drain where the seeds from a discarded starfruit take root and begin retaining moisture to lay the foundations for a miniature ecosystem suited to nematode worms, ants, and mosses. It can be a few square yards of actual vegetation—the raintrees along the roadside, the potted plants on balconies, the thickets of vines and creepers climbing the legs of the Ophir Road flyover … even the roof garden of the newly built megalomanic Marina Bay Sands Resort that looms in the haze like a latter-day Stonehenge. Or, the few larger greenspaces: pocket parks like the Kallang Riverside Park or relicts of rainforest, such as the Bukit Timah and Central Catchment Nature Reserves. A glance at Singapore’s map shows mostly forest fragmentation: scattered flecks and wisps of green among large swathes of the gray and brown of built-up areas.
Darwin Comes to Town Page 3