Managing Food Webs: Field Testing Systems Ecology

Systems ecology. Born of nuclear weapons production and the Cold War, forging science and engineering into an explanatory alloy of great power. Unprecedented insights into dynamics of tropical, tundra, desert, deep marine, and many other biomes were generated by systems ecologists. In systems dominated by humans, probably the most progress was made in terrestrial agroecology. Urban ecosystems turned out to be such a stew of economics, sociology, and biology that the tools of systems ecology provided few breakthroughs. Similarly, fisheries management, traditionally conducted on the basis of population biology, was a weak spot in the ecosystems armor.

But. Fisheries ecology, perhaps via aquacultural multidisciplinary bridge building, has made serious systems headway in the past couple of decades. Massive academic efforts have been thrown at characterizing and parameterizing a wide range of aquatic tropic webs around the world. An enormously successful estuarine restoration project (the Delaware Estuary Enhancement Program, http://www.pseg.com/info/environment/estuary.jsp) put a consortium of regulators, academics, consulting scientists, and other local and environmental stakeholders into play to institute a systems-driven impact offset of great overall value. And recently the Atlantic States Marine Fisheries Commission voted a deep reduction in the allowed harvest north Atlantic menhaden stocks.

Menhaden.  A schooling fish species not too small, not too large, just right to serve as a primary food source for predators ranging from barracuda to whales. And whose population behavior puts massive schools of lipid- and protein-rich fish not too deep, not too shallow, just at the right depth of the ocean to be the base of food chains yielding everything from commercially harvested mackerels, tuna and billfish to dolphins, porpoises, and squids. Really, really important component of the Atlantic marine ecosystem.

And a really important source of industrial materials as well. Massively harvested for processing into commercial fish bait, fish oil and protein meal and other useful materials. Valuable.

But vulnerable. A debated but substantive proportion of the annual menhaden production is being diverted from ecosystem to industry. How much to cut that diversion and how intensively to regulate the fishery were serious matters of debate. Remarkably, there was little debate, even among diverse stakeholders, over the need for some diversion.

Thus, the vote. The council voted heavily in favor of a 20% catch restriction and additional monitoring and population evaluation.

Score one for systems ecology. A field holding up on skinny legs in a world built on sturdy plinths of heavily funded subcellular engineering and molecular biochemistry. For a sustainable world, we need all our scientific tools, applied rationally, cogently, effectively. The wisdom and the will and the logistics and the politics involved in doing so are not going to be easy to come by. But maybe this menhaden decision is a sign that thing could shift in our direction. Let’s hope so!

Creative Methods for Biodiversity Maintenance

Last week we considered the potential for substituting holographic phantasms for actual individual organisms, from the perspective of making ecosystems seem psychologically whole even when they are physically depauperate. Unlikely, implausible and unsatisfying, you say? OK, you got me. But how about some more down-to-earth, practical yet oddball ideas for maintaining biodiversity in the face of powerful forces against? 

As I started this week’s column (9 December 2012), CBS Sunday Night news show “60 Minutes” ran a story about the desperate global network of specialists attempting to protect, preserve, breed and otherwise conserve increasingly rare and endangered species of turtles. Turtles are under pressure worldwide. In several trips to China involving series of more-or-less formal (and subsequently expensive) banquets, I have been fed at least 8 or 10 species of turtle, 3 of which I know to be critically endangered and a couple I have yet to identify so I’m not even certain they represent described and catalogued taxa!

Turtles are threatened both by harvest for food (of both eggs and adults), and for the illicit “pet” trade. Hobbyists are willing to pay enormous sums for individual animals, and the smaller the remnant populations, the more money the market will bear. At the moment, the answer for turtles, unfortunately, seems to be generally limited to habitat protection (expensive and often ineffective in the remote regions occupied by some species) and captive breeding. Despite administrative and technical challenges, the latter has so far seemed to keep at all species present and accounted for, even if only in artificially maintained colonies.

A couple of more interesting possibilities are available for certain other endangered animals. A web portal associated with American University (but otherwise of unknown provenance, http://www1.american.edu/TED/viagra.htm#r1 ) discusses the hope and hypothesis that Viagra and other legitimate anti-impotency medications might reduce pressure via traditional regional (primarily Asian) medicine on such reputed aphrodisiacs as rhinoceros horn. As the web site points out, many animal parts (such as tiger bone) are valued for other medicinal purposes and putative aphrodisiacs are only one class of traditional pharmaceuticals threatening animals and plants worldwide. I have myself witnessed the careless trade in endangered animal parts. Shops that I have frequented in Kuwait in search of tourist souvenirs and well-priced folk instruments from throughout Asia one night displayed a large shipment of raw (untanned) skins of tigers, leopards, wolves, and lions. I believe at least one of the lion skins was of the Asian variety, making it particularly rare. How and why a shop purveying dominoes, dart boards, and commercially made temple bells was suddenly offering a large stack of carnivore skins at bargain prices (I could have purchased a complete tiger skin of a large animal for the equivalent of a few hundred dollars U.S.) was and is beyond me.

But it does point to the ubiquitous and casual nature of the problem. In much of the developing world, poverty and isolation combine to minimize knowledge of and attention paid to conservation efforts. Someone who can sell a fortuitously encountered and killed tiger carcass for the equivalent of years or decades of normal earnings has powerful incentive to do so.

And thus we have the poaching wars in Africa. Increasingly sophisticated groups, sometimes with international logistical and funding support, hunt rhinos and elephants even where protection is a high priority and armed guards operate 24/7. 

Biodiversity problems are time-critical, in that on a species-specific basis there is a no-return threshold inherent in every population/density curve. Thus it is easy to sympathize with the gentleman attempting to protect his privately held rhinoceros conservation area by spiking the rhino horns, via several experimental technologies, with cyanide to limit their potential human uses (http://www.theweek.co.uk/politics/12775/put-cyanide-rhino-horn-one-way-deter-poachers ). 

Definitive quantitative linking biodiversity to sustainability are elusive, in many cases we don’t even know how to ask, much less answer, productive questions. That there IS such a relationship seems well beyond any scientific doubt. Seems to me that justifies a substantive level of financial, intellectual, and logistical investment. Precisely what that investment should be in a zero-sum, multiple-stressor world, may not be known or even knowable. Seems to me the more creative thinking we can throw at these problems, the better. What do you think?

4th Street

4th Street


The upgraded technology of early modern humans included enormous advances in weaponry. Worked stone tools went from clunky to intricate, with symmetrical, two-sided points, sharper edges, and more functional shapes. The atlatl, a lever used to throw spears with more power and accuracy, and the bolo, roped rocks thrown to entangle game, became important. Bone and antlers were worked for the first time, into such complicated forms as barbed harpoons and fish hooks. Soon after that, bows and arrows, snares and traps, and nets were invented. Thread and manufactured clothing (vs. animal skins) appeared about 20,000 years ago [1]. The basic human toolkit was nearly complete. 


If early modern humans led more settled lives than their forebears, it is at least partly thanks to the more effective environmental control their rich array of technologies provided. These tools also led some early sapiens to another life style that was to have important consequences later.


Modern humans tended to heavily exploit the most abundant large animals where and when they settled. Records show domination of remains in European sites by reindeer, red deer (in North America called elk), aurochs (wild cattle), horses, or ibex [2]. This may have pre-adapted groups sapiens for a life of following migratory herds. 


Large herbivorous mammals have many ecological advantages from the human perspective. They convert inedible vegetation into a nutritious package. Along with food, they provide very useful hide and bone. Milk, wool, and dung can all be harvested from living mammals. And herding animals, with predictable lifestyles and group socialization may be less dangerous to kill than their more individualistic brethren. 


As the ice age crept to its end, herding animals—reindeer, bison, mammoth, and horse—migrated between wintering grounds near the Black Sea and summer pastures in central Europe. Human settlements have been found along these migration routes. Humans learned to manage the herds for themselves. To keep from panicking masses of animals, people would drive a season’s worth away from the main herd for slaughter. The herd would also be culled for old or injured animals [1].


The big payoff came with animal management skills and associated cultural sophistication of the herd-followers. Humans and animals became linked socially as well as trophically. People learned to harvest the herds sustainably. Different groups of people would meet to slaughter and share, and the interpersonal interactions became important. Technological breadth increased— tools became more specialized for everything from handling hides to making wool clothing. Human intellect itself may have grown as people and animals became more closely linked. And herd-following was a crucial step on the way to development of agriculture [3].




Notes


[1] A compelling narrative of the technological transition and associated life style diversity is in Ponting, C. 1991. A Green History of the World: the Environment and the Collapse of Great Civilizations. Penguin Books, NY.


[2] Pyne, p. 28


[3] Pre-agricultural human progress is well described in Redman, C.L. 1999. Human Impact on Ancient Environments. University of Arizona Press, Tucson. 

3rd Street

3rd Street


When our ancestors settled in to occupy a site, even for a relatively short time, the first thing they did was establish a hearth. The hearth was important for warmth, nutrition, and social interaction: 


The earliest hearths are at least 790,000 years old, and some researchers think cooking may reach back more than 1.5 million years. Control of fire provided a new tool with several uses—including cooking, which led to a fundamental change in the early human diet. Cooking released nutrients in foods and made them easier to digest. It also rid some plants of poisons.
Over time, early humans began to gather at hearths and shelters to eat and socialize. As brains became larger and more complex, growing up took longer—requiring more parental care and the protective environment of a home. Expanding social networks led, eventually, to the complex social lives of modern humans [1]. 


For Homo erectus, hearths were temporary, located where needed to process the yield of successful hunts [2]. Some sites were occupied seasonally. Erectus took the social benefits of the hearth—campfires, really--with them on the road. When sufficient food was collected to justify it, a hearth and a “home”, however short-term, were created. 


Neanderthals, existing with and replacing erectus beginning about 250,000 years ago, were a more settled crowd. They lived in caves, tents, and mud-and-stick huts. Foraging out from where they lived, they brought food to the hearth. Likely this made the home more socially important. People learned more of their history, and of themselves, as they interacted around less temporary hearths.


Then Homo sapiens showed up. They were technologically advanced. Their weapons and tools were more varied and effective. They could start fires several ways, including by stone sparks, where Neanderthal could only twist wood drills. They were altogether more efficient hunters, more densely populated, and occupied more of the landscape. From the time sapiens spread throughout Neanderthal territory, the latter was probably doomed to extinction. It remains unclear precisely how and why neanderthalis disappeared. But occupation, assimilation, or competition, or all three, the mechanisms didn’t matter. Neanderthals were another large mammal species vaporized in the trail of modern humans. 


Or maybe not. About 20,000 years ago, human beings experienced massive cultural strides. This is the “Upper Paleolithic Revolution”, which saw enormous advances in tool and weapon technology, hearth construction, and especially, art and language. Much was happening in this time—climate was warming, sea levels, rising, human population density increasing [3]. It is possible—even likely—that social interactions themselves, feeding on increased communication among people living settled lives around familiar hearths, had important feedback effects that pushed culture forward [ ]. There is also a theory that interbreeding among sapiens and neanderthalensis was responsible for much of the revolution [5]. 


However it happened (and, like most things ecological, it is highly likely to have had multiple contributing causes), by the end of the last glaciation, humans were ready to take the next step toward the megacity.




Notes


[1] Quoted from (http://humanorigins.si.edu/evidence/behavior/hearths-shelters . I was led to this site by seeing the quote at http://www.historyofinformation.com/index.php , which is an outstanding web portal, carefully referenced, containing a constantly-updated wealth of information regarding the history of human information exchange.


[2] The framework of these paragraphs is from pages 27 – 29 in Pyne, S.J. 1997. Vestal Fire: An Environmental History, Told Through Fire, of Europe and Europe’s Encounter With the World. University of Washington Press, Seattle. 


[3] A good description of the Paleolithic changes in the state-of-the environment can be found in Cunliffe, B. 2008. Europe Between the Oceans. Yale University Press, New Haven. 


[4]


[5] Cochran, G. and H. Harpending. 2009. The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. Basic Books, NY. 

2nd Street

Here in the 21st century, humans are urban animals. Most of us live in cities, and the total urban population grows constantly, at the expense of rural areas [1]. This change is occurring worldwide—in North America, Asia, Europe, and across the southern hemisphere. 


One question worth asking is—how did we get here? Our distant ancestors are tree shrews—small, insectivore-like forest inhabitants [2]. Our closest ancestors are chimpanzees, jungle-dwelling, arboreal vegetarians with an occasional taste for a serious meal of meat. And here we are now, inhabiting densely packed cities about as far removed from jungle habitat as it is possible to get.


The evolutionary and cultural journey from the forests and savannahs of Africa to the megacities around the world today took time. But we became village dwellers early in our history, and it was just a few technological revolutions from there to the skyscraper. Well, maybe more than a few. 


The story involves three species in the genus Homo [5]. Homo erectus was possibly our immediate ancestor, walking upright on the African landscape nearly two million years ago. With large bodies and brains, erectus needed an energy-rich diet. Their family groups ate a high proportion of meat in addition to fruits and tubers gathered from wild plants. Lacking the claws, jaws, teeth, and strength of predators like saber-tooth cats and dire wolves, erectus had to innovate to capture, kill, and butcher animals. Homo erectus fossils are associated with some of the earliest stone tools, mostly sharp-edged multipurpose knives that might also have served as axe or spear heads. Fire was also a tool first associated with H. erectus. Fires were not only used for cooking meat (increasing its suitability as a food source), but were also social centers where conversation and other social interactions took place [6].  


With stone tools and fire at their service, clans of Homo erectus weren’t tied to the ancestral African plains. In travels that would be mirrored later by our own species, they emerged from Africa, establishing populations in Europe, the Middle East and parts of Asia. Maybe we needed the evolutionary practice to perfect the trick of global occupation.


Next up was Homo neanderthalensis [9]. They moved out of Africa and expanded across Europe and into the north, and made it as far as Siberia [8].  Neanderthalensis was a quintessential hunter, but also a gatherer. They lived in family groups, and were often sedentary in favorable habitats—thus their fame as “cave men”. Apparently not stupid, when they found good conditions, they stayed put. Evidence from sites dated 125,000 to 250,000 years ago in France suggests their diet included, in addition to large game animals, birds, fish and starchy vegetables [7]. Perhaps they sometimes migrated seasonally, and used certain sites annually on circuits following game or ripening food plants. The last Neanderthals lived in long-inhabited sites in the Mediterranean or the subarctic between about 35,000 and 28,000 years ago, depending on evidence yet-to-come [12].


A sedentary habit is the first step on the road to agriculture and true villages. But first came Homo sapiens Artemis, the hunter.


Between about 150,000 and 50,000 years ago, a few species (of a community of many species) of large land mammals went extinct in Africa and tropical Asia. Followed closely—between 50,000 and 10,000 years ago—by a large proportion of the large mammal species in North and South America and Australia. Between about 5,000 and 200 years ago, large animal species disappeared on Madagascar, New Zealand, and Pacific islands [13]. This pattern coincides precisely with the appearance of Homo sapiens in these regions. Likely the faunas of Africa and Asia suffered relatively few extinctions because modern humans evolved in and inhabited these areas side-by-side with the large mammals for most of our time. The mammals had time to adapt, to learn how not to be killed in massive numbers by hunting humans. 


Then people appeared rather suddenly and in large numbers in northwestern North America. South of the ice sheets were prairies, densely populated by large mammals including various kinds of horses, cattle, camels, rhinos, elephants, antelope, deer, glyptodonts (large, armored armadillo-like animals), cats, rodents and sloths. Similar, perhaps greater, diversity characterized South America. 


Within a few thousand years, as the climate warmed and people spread out geographically, much had gone wrong. Unused to human hunters, horses, rhinos, and elephants were gone completely, only a few species of antelope, cattle (bison, musk ox), camels (such as llama, alpaca and vicuna), big cats and deer remained. Of the rest, some survived as smaller remnants of their former glory—armadilloes, sloths, rodents. 


The pattern was repeated when people made it to Australia and Madagascar, and subsequently to New Zealand and Pacific Oceania. Modern human beings were formidable hunters, stalking the landscape for big game taking full advantage when they found it [14].


But humanity was not destined to live out its days in itinerant hunting. 




Notes


[1]


[2] There is some technical debate about this. The issues are laid out in a web portal of uncertain provenance, but well-referenced, at http://www.theprimata.com/tree_shrews.html


[3] A detailed dietary audit of chimpanzees, presented at a colloquium of the International Congress of Anthropological and Ethnological Sciences by faculty from the Department of Anthropology of Harvard University is available at 
http://cast.uark.edu/local/icaes/conferences/wburg/posters/nconklin/conklin.html


[4] Living things are classified in a system pioneered by Carl Linnaeus, a Swedish scientist in the 1700s. The “Linnaean System” retains the original Latin, and every species on earth is identified by a unique two-word name (the system is also called “binary nomenclature”), first the Genus, capitalized, which represents recognizably different species, lower case, the very organism under consideration. These names change as specialists debate relationships among animals and plants. The domestic dog is in the genus Canis, indicating its ancestry in the wolf clan, and usually the species familiaris, meaning familiar to us humans. Recently there has been a movement to link the domestic dog even closer to the wolf, as Canis lupus (species name for the gray wolf) in a subspecies, or variety, Canis lupus familiaris. Either way it’s the same animal, with a genome very similar to that of the wolf. The scientists may or may not sort it out to their satisfaction, for our purposes it’s enough to know that it’s our dog, companion animal recently evolved from the wild wolf. 


[5] The Smithsonian Institution provides an excellent and generally up-to-date and authoritative discussion of human ancestry at the web portal
http://humanorigins.si.edu/research


[6] http://humanorigins.si.edu/evidence/human-fossils/species/homo-erectus


[7] Hardy BL, Moncel M-H (2011) Neanderthal Use of Fish, Mammals, Birds, Starchy Plants and Wood 125-250,000 Years Ago. PLoS ONE 6(8): e23768. doi:10.1371/journal.pone.0023768


[8] Range maps of various provenance are available at http://news.nationalgeographic.com/news/2003/03/photogalleries/neanderthal/
and http://www.springerimages.com/Images/LifeSciences/1-10.1007_978-3-540-33761-4_56-1


[9] Some authors place neanderthalensis taxonomically as a subspecies of our own species, Homo sapiens neanderthalensis. This approach has credibility because of growing genetic evidence that sapiens and neanderthalensis interbred. Ability to interbreed is a common definition of a species. 


[10] 


[11]


[12] John Roach reported on evidence for the younger date on the Iberian Peninsula in National Geographic News on 13 September 2006, and on evidence for the older date in subarctic Russia on 13 May 2011. Both dates are subject to anthropological debate and additional finds are needed to sort things out.


[13] The history of large-mammal extinctions and the likely role of modern man in same is well presented and documented in Martin, P.S. 2005 Twilight of the Mammoths: Ice Age Extinctions and the Rewilding of North America. University of California Press, Berkeley. 


[14] The vision of modern human hunters as primary agents of extinction of large mammal faunas is not shared universally. Many anthropologists, sociologists, and some ecologists, find the assumption that pre-industrial humans could imbalance the ecosystem to that degree to be very unpalatable. A more benign view of the matter may be found in Delcourt, P.A. and H.R. Delcourt 2004. Prehistoric Native Americans and Ecological Change: Human Ecosystems in North America since the Pleistocene. Cambridge University Press, Cambridge, UK.

First Street--Urban Ecosystems Chapter 1

Here’s the first chapter following the prologue in the draft of the urban ecosystems book.


First Street


Systems ecologists operate like engineers let loose on the natural world [1]. We like to envision things as storage boxes, but our boxes have machines inside. Matter and energy go into the box, are transformed by the machine, some is tucked away for later, some is sent back out. Think of a “thing”, say, a dog. Food and water in, heat, feces, urine, and, (often what seems like too much), energy out. To a systems ecologist, a dog is a storage box (for dog flesh and bones) with a food transformer inside.


It is no random coincidence that the field of systems ecology is related to engineering. Systems ecology was born with the enormous engineering feats of the nuclear weapons programs of World War Two and the Cold War. One outcome of nuclear and thermonuclear detonations was the sudden appearance of otherwise rare radioactive materials in the environment. These chemicals acted as radiotracers—they could be tracked through the ecosystem. Known half-lives and other chemical properties allowed us to quantify biological processes that had previously been intractable. Suddenly, we could see the biological world as an organized, interactive, hierarchical, integrated system. Cells, organisms, populations of organisms, communities of populations all had a place in this new view of the world. The term ecosystem, coined in the 1930s, applied to the relationship of organisms and their physical and chemical environments [2]. By the 1950s, it was clear that ecosystems had far broader meaning and many more dimensions.


This was something of a shock. Until that time, ecologists operated in subfields—plant or animal, fish or mammal, worm or microbe. And our primary tool was counting. How many animals or plants (or species of mammals or worms or…) are found in this habitat? If the habitat is changed, how do the numbers of species and numbers of individuals of each species change? Now we were thrown into a world where deconstructing biology into component parts was inadequate study design. 


We no longer did ecology by enumeration. In addition to radiotracers, we had begun to use calorimetry—measurement of energy content—to explore ecosystems. We realized that physical laws—the laws of thermodynamics—applied not just generally, they applied very specifically to the living world. We could track the flux of energy through ecosystems, from sun to plants to herbivores to carnivores. We were able to understand, as one ecologist put it, “why big fierce animals are rare” [3]. In part it is because energy transfer is inefficient. In moving from plants at the bottom to carnivores at the top of the food chain, roughly 50% to 90% of energy potentially available is lost at each transformation. There is a “heat penalty” paid when matter or energy transforms. Heat is the great energy sink of the universe. To get a unit of energy from the next step down in the food chain, you have to invest half or more of the energy to pay that penalty. Physics places fundamental constraints on biology.


And puts new tools in the scientific toolkit. Input/output analysis, where we learn about the machine-in-the-box by measuring what happens to ins when they come out. Feedback quantification, finding processes in the box that increase (positive feedback) or decrease (negative feedback) inputs. Forcing functions, parameters that change the system from the outside.  


In research labs in the 1960s and 1970s, there were ongoing debates over what constituted a proper ecosystem. We argued over endless pizzas and pitchers of beer. Ponds and lakes were ecosystems, we agreed. They had definable boundaries, and processes in the ecosystem (under water) were different from those outside. Could a mud bar where a stream entered a pond be an ecosystem? It wasn’t clear. A forest watershed could be an ecosystem. Could a standing dead tree be one? How about a fallen tree trunk on the forest floor? An area of wind-blown dune in a dry desert? The arctic tundra is an ecosystem. Is an iceberg?


To this day, there is no generally-agreed definition of an ecosystem. This is probably as close as possible: an ecosystem is an area with identifiable boundaries, with processes more active within and beyond than across the boundaries. The boundary acts as a filter, the environment within the boundary differs in measurable ways from that outside.


This is a very empirical definition. And it is not foolproof. A single cell could be an ecosystem under this definition, but is generally not thought of as such. However, a road-killed opossum, decomposing on grassy shoulder, probably is. Ponds, lakes and watersheds? For sure. Cities? Definitely.


Notes


[1] Parts of this chapter appeared in different form in Ludwig and Iannuzzi 2011.


[2] 


[3]

Urban Ecosystems and Urban People

A few years ago, several of us banded together and proposed to write a text on urban ecosystems for a major academic publisher. For various reasons, it fell to me to draft a rough-out of the manuscript for my co-authors to build their material into. For various reasons, having largely to do with sloth, procrastination, and the need to earn an actual living, I failed to do so. For various reasons, we have revived our own and the publisher’s interest in this manuscript. 


However, it turns out that in the interim, a number of nominally competing books on urban ecosystems have been published. I bought ‘em all. They are uniformly expensive, intensely academic, and generally dull. In other words, intended to serve primarily as texts for classes taught by the authors. Since we don’t have such constraints, and would far prefer to render the fascinating field of urban ecology in a form digestible by a more general audience, we’ve revised our target readership. In keeping with the zeitgeist, we thought to write it so it can be read in small bites by people who spend too much time dealing with too many bytes. In fact, we’re drafting it as brief, weblog-like chapters. Which yields a perfect motivation for finishing up this damned draft. I’ll start posting chapters weekly here until the book is complete. First installation—the Prologue—is below. We’ll go chapter-by-chapter from here.


Prologue


Years ago, one of us—Ludwig—had business in the seaside city of Aqaba on the Gulf coast of southern Jordan. It took most of a day for my colleague and me to be driven down the ancient King’s Highway from Amman. We arrived late in the afternoon and gave our drivers the evening off. After checking in to our hotel, we wandered the town, keeping to the seaside road.


We came upon what seemed to be a vacant lot tucked into a shoreline corner between the beach and a canal that ran back into the city. On closer inspection, it turned out to be an archaeological site. Under excavation was a street from an ancient town, with the foundations of small, rectangular buildings built wall to wall. Informative signs identified the town’s souk (market), and explained the architecture of the buildings. Most were combinations of commercial space—shops or storehouses—with residences. With the quiet waters of the Gulf of Aqaba meters away, and the sun setting behind some date palms, it was easy to imagine life in the trading town of Ayla around 600 AD. 


Older ruins—dating to Roman times and beyond, possibly to the middle of the first millennium BC—were reputed to be nearby on the shore. Within Ayla itself, the narrow street with open building fronts didn’t seem that different from a modern souk in the crowded alleys of any Middle Eastern city. You could feel the heat of the day slipping away as the markets opened, smell the dates and lemons for sale, hear the calls of the cloth-sellers and metal workers. Ayla was one of the first conquests of the Islamic Caliphate rising from Arabia. Its part on the world stage didn’t change much, only the place taxes were sent. Ayla remained a busy trading crossroads where land and water transportation met. Small industry prospered. The population supported itself on the combination of local produce and import/export business. 


It immediately occurred to us to seek the sources of fresh water and agricultural production that kept Ayla going. Alas, these hinterlands—except for the waters of the Gulf itself, which undoubtedly provided fish and shellfish--are now buried beneath infrastructure of the modern city. But it occurred to us that, at least in pre-Roman times when trade was likely a smaller proportion of the city’s life support system, it must have been a tough place to support a sizeable population.


And what was that population size? Well, it fluctuated, depending on whether Ayla was in the trading route mainstream or sidelined by alternatives. It may have fluctuated with climate, as well, which varied over the life of the town which extended from at least 1500 BC to near 1500 AD. Absolute population figures are not available. The infrastructure as I saw it could probably support no more than a few thousand individuals, including local providers of food, water, raw materials, and products. But the fact remains: this was a city on a body of salt water backed against a desert. Not the most propitious place for a city.


Consider the problems such a location entails. Fresh water is hard to come by. Pasture land is sparse.  Trash doesn’t decompose in the salty soils. The air may be humid, at least spot-on the coast, but it carries the constant winds and grinding sands of the desert. And the location is exposed, from both land and sea, to invaders.


We were struck by the oddity of the location, and shocked at how much like a modern city Ayla looked. Many of our questions—why this particular place? How did they provision? What did it cost someone—in time, money, effort, risk—to live here? What benefits made the investments worthwhile?—were similar to the questions systems ecologist ask all the time. 


Until that warm sunset on the Aqaba shoreline, it hadn’t occurred to us to think of cities as ecosystems. After that, we never thought of them any other way.


Notes


[1] a briefing-level history of Ayla is available at http://www.unesco.org/csi/act/jordan/preproject.htm


[2] a more detailed account built from a report of sequential archeological excavations is at http://oi.uchicago.edu/research/pubs/ar/91-92/aqaba.html


[3] a detailed discussion of population characteristics, but not size, is “Scholars and Society at Early Islamic Ayla.” Journal of the Economic and Social History of the Orient 38 (1995): 417-428. Presently available at http://upenn.academia.edu/PaulMCobb/Papers/445308/Scholars_and_Society_at_Early_Islamic_Ayla