Roopnarine, P. D. 2009. Ecological modeling of paleocommunity food webs. in G. Dietl and K. Flessa, eds., Conservation Paleobiology, The Paleontological Society Papers, 15: 195-220.

Just published, this paper discusses some of our network work in detail. You download it here or here.

You are looking at the food web of a terrestrial community from South Africa, some 250 million years ago. This ecosystem was the culmination of more than 50 million years of coevolution among rapidly diversifying groups of forest plants, insects, reptiles, and our proto-mammalian ancestors. This is a very informative way to depict the community, showing the predator-prey relationships among the organisms within the ecosystem. The world at this point in time is perhaps well on its way to our modern world: globally on the cool side and “mammal”-dominated. But it all comes to a rather abrupt end when Siberia opens up. Sometime between 251 and 250 million years ago, a gigantic plume of magma began to erupt from deep within the Earth, reaching the surface in the region roughly equivalent to Siberia in today’s world. Lava flowed onto the surface for thousands of years, eventually reaching a volume almost equal to the entire continent of Europe! The physical and chemical changes on the planet were extreme and profound, as were the extinctions. More than 90% of all species known in the oceans, and more than 70% of animals known from land as fossils, became extinct. It is the largest extinction recorded in the fossil record.

My co-workers and I have modeled the way in which these geophysical changes would have affected our South African community, by constructing detailed, dynamic food web networks. I should point out here that a lot of this work has been conducted by graduate and undergraduate students in my lab, including two interns funded by NSF’s REU Summer Systematics Institute here at the California Academy of Sciences. Students have been involved in every aspect of the work, formulating theory, collecting basic systematic and ecological data, conducting simulations and analyses, and even writing computer code! When we applied our model to the South African community, we discovered a couple of interesting things:

1. One way to examine cascading changes through a network is to simply perturb the network, and observe the chain reaction in a house-of-cards fashion. This is the manner in which currently popular analyses of network robustness have been conducted, such as robustness of the internet or airline transportation systems, in addition to food webs. When we do this with our South African network, the result is a reasonably linear and predictable response, and the implication is that the extinctions could only be explained by an almost complete loss of primary production (plant food). This does not agree with the geological record, so we don’t trust the result. And there is another very good reason to not trust this result, and it’s why we cannot always use such a simplistic approach when thinking about biological, including human, networks. This model assumes that the interactors in the network are unintelligent, that is, they do not respond or adapt to the changes taking place around them.



2. We addressed this by using very simple ecological interactions among the species in our community. The interactions are based on straightforward ecological common sense. The result is strikingly different when we assume that our species would respond ecologically to the other species around them. The result has a tipping point!

We’ll delve into this very interesting result in the next post.

Good, did that get your attention? I’m interrupting my “Six Degrees” series of posts to address a topic that has been in the news recently. That topic is the supposedly new observation or conclusion that the planet is cooling, in opposition to the warming trend. For example, the BBC ran this piece entitled “What happened to global warming?”. The answer, in a nutshell, is NOTHING. The article has stirred up quite a bit of argument and discussion between proponents and skeptics of global warming. So what’s all the fuss about? I’ll try to explain. But first, let me be blunt: the natural world does not give a fig about our opinions, whether we support (”believe in”) or deny (see here) human-caused global warming.

Okay, so what is this about? The Earth’s climate is a dynamic system, meaning that it evolves over time, and at any given time may be considered to be in a particular state. One of the major drivers or controllers of climate is the world ocean, primarily because the ocean is the planet’s major heat sink. This is the result of water’s high heat capacity. To understand this, think about a pot of water boiling on your stove. You watch it, and it just sits there. Now suppose one stuck one’s hand into the flame (Readers: Do not try this at home). Gee, your hand heated up pretty quickly! Not so with the water. But eventually, the water absorbs enough heat energy to begin it’s transition from the liquid state to a vapour state; that is, it boils. It takes a lot of energy to change the temperature of water. That’s just one wonderful property due to water’s fantastic molecular structure. The world ocean covers 70% of the planet’s surface, and it’s movement is the global movement of heat.

The oceans are dynamic; they flow, they mix, they churn. One could say that our understanding of long-term ocean dynamics is still very incomplete, but we do know that there is long-term variability in the states of the world ocean, and hence in climate. Perhaps the most familiar manifestation of this is the El Niño-La Niña quasi-cycle. Another is the less familiar Pacific Decadal Oscillation, or PDO. These phenomena represent natural variability in the ocean’s circulation. The variation translates into climate variability. We’ve seen these cycles operate through the 20th century. The century began a bit on the warm side, but cooled globally, on average, from the 1940’s through 1970’s. The variation is caused by the ocean sloshing back and forth. Now the sloshing is causing cooling once more.

THIS IS UNRELATED TO THE TREND OF HUMAN-DRIVEN GLOBAL WARMING. Let me say this again: This is not a reversal, nor is it refutation of anthropogenic global warming. How do I know this? Science folks. The media really should speak with the scientists doing the research, rather than sensationalizing and immediately seeking the nonsensical sound bytes of dwellers on the fringe. The cooling has been noted for some time (I blogged about it almost a year ago!), and we know that it is being driven by the PDO. Now here’s the cool part. We can tease apart this natural variability and other influences, so-called external forcings. This means that we can look at global temperature, and ask how much of it is due to the ocean driver, and how much to external factors. Should I tell you what the answer is? Can you guess? IT’S STILL WARMING. Overlain on the natural variability of our climate is a clear upward trend through the 20th century.

Don’t believe me? Show your friendly neighbourhood scientists a little love and read one of the original studies here. ‘Nuf said.

In the previous post I promised to explain the lengthy answer to the Kevin Bacon riddle posed in the first post. Here’s a start…

Let’s take a short trip through food webs, ecosystem collapses, and the bottom-up approach to making new scientists. We’ll begin by looking at tropical coral reefs, the most species-rich ecosystems in modern oceans. Coral reef communities are important reservoirs of biodiversity, and they are of extreme economic importance to many human communities because of tourism and fisheries. They are also one of the most critically endangered ocean systems, and in the last couple of decades we have witnessed the rather sudden transition of many of these systems from diverse, coral-dominated systems, to species-poor, algae-dominated systems. These transitions have been attributed to a number of factors, most notably overfishing of high trophic level species, pollution and pollution-driven diseases, and most recently, ocean warming and acidification because of global warming. But as many scientists have documented, reefs as we know them today are mere shadows of what they were hundreds, and perhaps even thousands of years ago. The footprint of human impact is really a long highway. There is no doubt that transitions are occurring today though, because we are witnessing them. Why now?

Take a look at the heuristic image. This is known mathematically as a catastrophe manifold, and it’s a very useful way to visualize what’s happened recently to some Caribbean reefs. Those reefs, which historically have withstood years of battering hurricanes, are now vulnerable to severe storm damage. The major reason is that the removal of large herbivorous fish, grazers of algae, allows large algae to take over large areas of the reef after a storm has passed through. The algae reproduce and spread much more rapidly than do the coral. Under normal circumstances, suppression of the algae by the fish allow the coral to thrive and construct the important reef habitat. The important take home messages for us are:

1. 1. The transitions from coral to algae dominance are the result of cumulative impacts, and though the state of the system appears to be stable, an erosion of its internal stability is taking place.
2. 2. When a transition occurs, it can be quite sudden; it’s a surprise! And indeed, these transitions tend to occur within a few years.

Now the precise manner in which this all happens is of great interest to answering the riddle of Mr. Bacon and science education. It all has to do with networks of interaction and relationships, and the ways in which you can spread, or cascade, through those networks. I’ll illustrate this in the next post by yanking you back into the past, way back (250+ million years), to one of Earth’s most interesting times, the Late Permian.

In the meantime, take a look at some of my recent work on coral reefs. You can also read a rant about networks here.

This post continued from the previous…

Reference to”small-world” networks in the previous post is only part of the riddle, also posted previously (i.e. What do Kevin Bacon, Adolf Hitler, ecosystems and science education have in common?). What does all this have to do with responsible science? With particular reference to scientists who address ecosystems and environmental issues in their research, the answer can be presented in three parts. First consider that the human and natural worlds today are facing challenges unprecedented in human history. The three most significant of these challenges are:

1. 1. Anthropogenically-driven global warming and climate change.
2. 2. The accelerating damage to ecosystems and loss of ecosystem services, characterized most frequently by the accelerating extinction of species.
3. 3. Continuing increase of the rate of global population growth, and perhaps more seriously, a continuing increase of the rate of per capita human consumption of non-renewable, or slowly renewing, natural resources.

Second, there are deep similarities between the ways in which the parts of ecosystems function, and the small world of humans. Not only can they both be represented by networks, but the mathematics are very similar! Unfortunately, the fallout from this observation is not all good. And third, if scientists wish to really leverage our knowledge and be responsible citizens of the planet, then one place to begin is to use the power of the small world to our advantage.

I’ll explain this rather lengthy answer to the riddle in the next post, where we’ll take a short trip through food webs, ecosystem collapses, and eventually the bottom-up approach to making new scientists.

The following post is based on a presentation that I gave early last month (August 2009). The occasion was a symposium of NSF REU summer programs in the San Francisco Bay area. The California Academy of Sciences hosts the oldest such program in the region, the Summer Systematics Institute. I was asked to give the keynote presentation. I thought for sometime about what would be an appropriate topic for an audience of my peers and very bright and industrious young college students. I decided to chat about networks (of course), the opportunities available to scientists as humans in the modern world, and the responsibility of scientists toward that world. I’d like to share this essay with my readers, and will do so over the next few posts. So here it is…

Let’s begin with a riddle. What do Kevin Bacon, Adolf Hitler, ecosystems and science education have in common? If we count persons that I know personally, then I am only 3 steps, or links, removed from both Hitler and Mr. Bacon. Now, for those of you who may know me, and are disturbed by your newly discovered connection to Hitler, or maybe Mr. Bacon, don’t worry; I am only 4 steps removed from Mahatma Gandhi. I find these facts to be remarkable given that I grew up in a world of 6 billion humans. Doubtless, many of you have heard of the 6 degrees of Kevin Bacon game, where so many Hollywood actors, and by extension you and I, are on average only 6 steps removed from Mr. Bacon. This is, again on average, true of the global human population. Even as the global population grows toward 10 billion, we are learning that we live in a small world, and that the world is in fact becoming smaller for many of us.

This idea can be illustrated very nicely with graph theory and network visualizations. Imagine a network, or neighbourhood, where each person knows only their immediate neighbours. In order to get to know the person furthest removed from you, you have to become acquainted with (N-2)/2 other people (where N is the total number of people). This distance grows with the size of the population. If we assume, however, that there is some small chance that you know someone at some distance, a very social neighbour for example, and we add that connection, Voila! The number of steps now falls dramatically. A family acquaintance who writes Indian literature is my link to the Mahatma. Note that these results cannot be obtained by simply randomizing the network; on average, those paths would still be pretty long. What we can do, by adding a few links strategically, or by creating a person who is a real social hub, is to create a small world. That’s why I am so close to Mr. Bacon. His friends call him Kevin.

(The first image is from the BBC’s “Six Degrees of Separation”)

The relationship between population size and anthropogenically-driven climate change is problematic, and definitely not straightforward. Controlling population growth, while balancing increasing resource utilization, shrinking resources, the desire and capacity for improved living conditions, and the state of the natural world, is challenging to say the least. Each one of these issues is complex by itself, and taken together they form the most complex system that society has to deal with. The solutions are not obvious, and below I’ll try to outline some of the dilemna.

Let’s say for the moment that, with regard to climate change, each individual or society as a whole can adopt one of several simplified strategies. One can either deny or accept anthropogenic climate change, and one can either do nothing, or do something. That gives us several joint approaches:

1. 1. Deny and do nothing. This approach is still with us, but is thankfully becoming more of a historic anachronism. It is not an unreasonable approach if placed within the proper context — the past. Without evidence that climate is changing, why would we do anything about it? Practically, one should continue on with business as usual, especially if that business is beneficial to the societal good. This has been the prefered strategy for most of humanity’s history. Today, however, no intelligent mind can deny the reality of ongoing climate change, and this strategy is therefore obsolete.
2. 2. Deny and do something. This approach is listed for combinatoric completeness, but it really does not make any sense, unless, I suppose, one is in a position where there is an obligation or responsibility for going along with someone else’s strategy. This could be the case for leaders who are encouraged, coerced or forced into action against their beliefs, or citizens who must comply with societal decisions. I suspect that, at least in the United States, this will be the eventual fate of skeptics who, supported by misguided confidence in their abilities to understand the problem, will never listen to scientific or societal reason (for some particularly mind-boggling examples, check here and here).
3. 3. Accept and do nothing. I think of this as a transition strategy, and the one that society has been using for the last century or so. The first cautions about climate change date to the 19th century, but as we know, it is only within the last couple of decades that the problem has seen broad acceptance. Again, this is perfectly reasonable. First, scientifically-speaking, demonstrating recent anthropogenically-driven climate change has been very difficult. Furthermore, making predictions of future impacts, as well as developing joint scientific, economic and political solutions remain fraught with uncertainty. Second, the cost of doing nothing has so far been rather small, or at least has appeared to be small. In spite of numerous challenges, the scientific, economic and political revolutions of the last 200 years have resulted in broad (though disparate) increases in  global prosperity and population growth. There is, however, no free lunch in the Universe. The Earth’s resources are finite. This is easy to recognize when we consider resources such as fossil fuels, utilizable land, mineral resources, and so on. It is much more difficult, however, to recognize and accept that a far more important resource is the state of the global ecosystem. Our ability to exploit simple resources, and grow the human population, is predicated on a stable and predictable global ecosystem. All our activities take place within the context of ecosystem services and stability, and are meaningless, in fact impossible, without such context. Unfortunately, the do nothing approach is changing the context, and we can no longer maintain this strategy while enjoying increased prosperity and population growth. There are simply too many of us, and we consume too much.
4. 4. Accept and do something. This of course is the strategy which we must now adopt. That much is simple, but the strategy itself is not simple. What do we do? First, we must strive ever more diligently to understand the scientific and societal complexities of the joint human-natural worlds. Second, we must mitigate the activities that have led us from the Deny strategies to the forced Accept strategies. Notably, we must reduce those activities that are eroding the systems, namely our heavy reliance on fossil fuels and continued exponential growth of the human global population. Third, we must evaluate carefully the cost of those reductions to human prosperity. Finally, however, we must weigh, as honestly as we can, those costs against the costs to human prosperity of doing nothing. And remember, human prosperity is ultimately and completely dependent upon the state of the global ecosystem.

Sadly, as the recent proclamations of the G8 leaders make all too clear, we are currently stuck between strategies 3 and 4: Accept and maybe do something. “Something” translates to not enough. We are selling long-term prosperity and stability for short-term economic gain. The United States has once again failed to step up to its role as a world leader, and thereby seize the economic and political opportunities that could be realized for its people. Instead, the prosperity of the people are held hostage to the interests of a few (societally uninterested) corporations, irresponsible international partners, and a domestic minority of pseudo-intellectual dimwits. The resulting world can most certainly exist, but it will not be pleasant. We will trade the potential of the human condition for what Robert May has aptly described as, “the Blade Runner world”.

Malthus‘ gloomy outlook on the consequences of unchecked population growth has found many champions in recent decades, perhaps most notably Paul Ehrlich. This must be the result of the tremendous growth of both national and global populations in the 20th century. Modern examinations of the consequences take both historical and prophetic tones. Jared Diamond, in “Collapse“, relates chilling tales of environmental exploitation gone wild in historical societies, such as the Maya, Greenland Norsemen, and the Polynesians of Easter Island. Ehrlich warned us more than 30 years ago (”The Population Bomb“) of the coming collapse of modern societies should population growth remain unchecked. Yet, here we are; we’re still here, and the growth of the global human population is accelerating. Why then should we listen to Malthus and his modern counterparts?

The notion that the human population can continue to grow without limit is simply illogical. As I pointed out in my previous post, non-human populations in nature can never sustain Malthusian growth. So why have we humans seemingly accomplished this over the past few centuries? Are we special? Yes and no. First, let’s take a look at how we’ve manged it.

Modern human society has at least three advantages over its predecessors: increased food production, reduced mortality from disease, and increased security. I suspect that the global population growth rate probably began to accelerate as agriculture was developed in different places, which are historically fairly recent events. More food equates to more people; surpluses support population growth and larger populations. In more recent times, humans have become increasingly efficient at suppressing and reducing mortality due to diseases, especially those caused by infectious agents. The growth of civilized societies (if we choose to define civilized as living in cities) was also often accompanied by increased security and reduced mortality from human aggression. Yes, believe it or not, today we do a far better job of feeding large segments of the global population, controlling epidemics, and keeping ourselves safe from murderous neighbours (both domestic and foreign). Famines no longer sweep through Europe, smallpox has been eradicated in the wild, and wars tend not to last Thirty Years.

Yet one can’t help but get the feeling that things are cracking at the seams. Food shortages have reached crisis levels in many regions. The Black Death probably required several decades to make its initial journey from Asia to Europe in the 14th century, while today we worry about the spread of a global pandemic on a timescale of weeks. And sadly, we now have the capacity to kill thousands daily with conventional warfare, and millions within minutes with weapons of mass destruction. Are these cracks related to population growth? Is the human population reaching a carrying capacity limit? I think that these are very difficult questions to answer, but the answers in my opinion are both yes. There is no shortage of people who are ready to disagree with me, and some of them will point to very clever arguments (all of which I judge to nevertheless be without merit). We’ll explore the questions, arguments and counter-arguments in subsequent posts, as well as the connection to global warming and climate change. In the meantime, check out this very entertaining link.

Sung to the tune of Happy Birthday (of course):

Happy Earth Day to you,
May you live in a zoo.
We descended from monkeys,
Bacteria and goo.

Thomas Robert Malthus (1766-1834) is perhaps one of the most underappreciated intellectual giants of the 18-19th centuries’ revolution in Western thought. Malthus lived in an age of revolutions; social, political, economic and, of course, scientific. Malthus is best known for his answer to a seemingly simple question (see An Essay on the Principle of Population): Given a particular birth rate, what is the expected growth of a population? Malthus formulated the equally simple answer based on the observation that population growth is multiplicative, i.e. if the average parent organism produces more than one offspring, then the population will grow exponentially over time (Fig. 1). Malthus then made an important leap, pointing out that the Earth, at least in his day, was not overrun by any particular species, and that this was due to resource limitation. Population size is therefore limited by competition among individuals for limited resources. Later on, Malthus’ observations would inspire Charles Darwin’s brilliant formulation of the struggle for existence, and the process of evolution by natural selection. Those observations, along with Darwin’s (who was as gifted an ecologist as he was gifted geologist and father of modern evolutionary biology), also inspired the 20th century fields of population biology and community ecology.

Malthus’s speculation was formulated most powerfully in 1838 with the Verhulst logistic equation, which captures Malthus’ notion of limited resources mathematically. The logistic equation expresses the limitation or slowing down of population growth as population size increases, predicting that size will eventually reach a stable point which is maximally sustainable given available resources (”carrying capacity”) (Fig. 2). In nature, resources may include items such as access to sunlight, water, food, and even sheltered from predators and parasites. The real situation is a bit more complicated, and populations in the wild vary wildly sometimes (see earlier post) but, in general, Malthusian population growth is believed to be absent in nature. Or is it?

The global human population at the start of the 20th century was approximately 2 billion. Imagine this: since Homo sapiens evolved, say 150 thousand years ago, we have gone from perhaps a few dozen individuals, through wars, famine, plague and natural catastrophes, to 2 billion individuals. By the end of the 20th century, in the span of 100 years, the global population increased from 2 to 6 billion humans (Figure 3). It is clear that humans have violated Malthus’ principle. Are our resources unlimited? Hardly. We have continued to be innovative in resource exploitation, and we have also greatly reduced the impact of limiting factors such as predation an disease. Is Malthus now irrelevant as far as humans are concerned? Hardly. The single root cause of all our environmental problems, and many socio-economic and political ones as well, is population growth. The reluctance of many, including environmentalists and champions of good causes, to acknowledge this is nothing short of astounding. Reducing the per capita carbon footprint will be meaningless in the long-term if we have 10-12 billion humans on the planet by the end of this century.

I would like to explore this issue of population growth on the blog. The next several posts will raise some of the questions on my mind, but it is clear that this is a very complicated and sensitive issue. I invite readers to join in the conversation, and to participate with comments and questions of their own.