I just received a letter, notifying me of an unsettling event in my life. The letter was from an airline, congratulating me on meeting the requirements for their next tier of loyalty membership. In the past year, I’ve apparently flown 28,000 miles on 21 segments, with just this one carrier. My best guess is that my total travel for the year is closer to 40,000 or 50,000 miles. I got on an airplane for the first time at the end of high school, and never imagined this life.
The letter bothered me, and it took some time to understand why. At first glance, the letter feels like a congratulatory note. It is a privilege and a joy to travel so much. Each new ecosystem I’ve seen over the past years has widened my understanding of how the world works, and I wouldn’t easily trade that away. This kind of travel is essential to do good ecology. Charles Darwin spent five years in and around South America; Alexander von Humboldt spent several years exploring Latin America and north; Alfred Russell Wallace lost himself in Amazonia during his youth and later spent a decade wandering through the Malay Archipelago. Deep understandings of ecosystems require firsthand experience – what airplanes give us is simply the opportunity to reach them faster and more comfortably. Think of Wallace, for example – his trans-Atlantic journey home from the Amazon was nearly fatal, when his ship caught fire after twenty-six days at sea, leading to the ship being abandoned and a ten-day journey in open boat before being sighted and rescued. He lost nearly all his specimens, representing four years of exploration. I am glad to have avoided this experience. There are very few parts of the world – even very wild parts – that now are inaccessible with a journey of more than a few days.
It is not the resource usage of this air travel that bothers me. The environmental impact of flying is large, and my carbon footprint is certainly larger than that of almost all people. But nearly all this travel has been for research, and I am a firm believer in the importance of investing in new knowledge. Scientific discoveries, when they are made, last forever, and are open for all to share in (at least eventually, but that is the subject of another piece). New ecological knowledge requires fieldwork and interaction with others, and this requires travel. Imagine telling a young Darwin not to go to the Galapagos, because of the resources wasted in a ship voyage. As a research community we push forward the frontiers of knowledge, and it is very difficult, in advance, to know which one of us, or which piece of work, will be the transformative one. Investment in exploration and collaboration is fundamentally necessary. A recent publication showed that there is embarrassingly little known about some parts of the world, because ecologists don’t go there to study them – urban areas, for one, but also very wild areas.
What bothered me was a different aspect of seeing so many places. Divide 365 days by 21 flights (a lower bound; probably closer to forty) and you’ll see that on average I spend just a few weeks at most in a single place. It is very hard to build a community, a life, or a deep understanding of a place in such a short time. I have felt exhausted by this whirlwind approach to science, and my airline’s letter only confirmed the reality of the situation. To remain in one place is to begin to feel its rhythms and to begin to know it more personally. Aldo Leopold writes about this in his A Sand County Almanac, describing the changes in a landscape over a year, and so does Edward Abbey in Desert Solitaire, sketching a season spent in the desert. Much of the best ecological research comes from long-term, in-depth study of single places, and many of the best ecologists have devoted their careers to knowing single places. Wallace would never have discovered the biogeographic break in Australasia in just a few weeks’ time.
I’ve spent the past four summers in the Colorado Rockies, but I’ve only seen the autumn once and the winter snows never. Summer hailstorms like the one above are rare events, and I’m sure there’s far more I’m missing out on understanding during the rest of the year. I think it’s time to quit airports and stay in one place for a while.
Day three of the INTECOL / British Ecological Society meeting here in London. I was asked to give a talk on a paper that influenced my thinking as an ecologist. Biology was never what I expected to do – I started out in physics, then found that ecology was closer to my heart – more immediately relevant questions and more tangible scales. More beautiful and casual places to work, too – here I am with a Fuchsia flower in the Andes.
Anderson writes about the danger of reductionism in science. Reductionism is the idea that a system can be better understood by breaking it into simpler pieces – for example, understanding chemistry by studying atoms, understanding atoms by studying particle physics, understanding particles by studying string theory, and so on. Coming from physics, I naturally thought that ecology could be studied the same way – take apart a very complex system, study its part, and then reconstruct the workings of the whole. But things are not always so simple. Anderson writes,
The main fallacy in this kind of thinking is that the reductionist hypothesis does not by any means imply a “constructionist” one: The ability to reduce everything to simple fundamental laws does not imply the ability to start from those laws and reconstruct the universe. In fact, the more the elementary particle physicist tells us about the nature of fundamental laws, the less relevance they seem to have to the very real problems of the rest of science, much less to those of society …
But it’s not immediately obvious what approach should work best for ecology. The field has historically been dominated by two perspectives. One is a holistic viewpoint, emphasizing the overwhelming complexity of natural systems, Darwin’s ‘entangled bank’ of diversity. This approach is not useful for synthesis or prediction, since it explicitly denies such an approach can work. The other perspective is that same reductionism, a popular viewpoint in past decades that claimed that ecosystems could be controlled, managed, and subdued. As, for example, in this 1968 photograph by Robert Adams entitled Colorado Springs, Colorado:
But the approach that has brought us the moon landings and the sequencing of the human genome may not work so well for ecology – somewhere between holism and reductionism is the constructive science we need. On one hand, we have ideas like West, Brown, and Enquist’s metabolic scaling theory or Harte’s maximum entropy theory, which argue that simple mathematics and simple variables (like body mass, or total species richness) can explain a wide range of macroecological patterns like the energy usage of organisms and the rarity of individuals. We also have developments in population biology (for example, Tony Ives’ recent work on fluctuations in midge populations in lakes) that involve complex modeling and single scales of analysis, but that make very accurate predictions. But theory has its limitations – for example, dynamic global vegetation models, which make predictions about how carbon storage by forests will respond to climate change, require many scales of modeling to make any progress, yet still make predictions for the next century that range from an increase of five or six billion tonnes of carbon per year to a decrease of the same amount. So then, what is the right way forward?
I now think that bridging scales is critical in building a more predictive ecological science. To focus on one scale, to build reductionist models (think a simulation of every gene in an organism, or every tree in a forest) are probably not the right approach. We have to find different ways to construct our understandings. Anderson argues,
… we have yet to recover from [the arrogance] of some molecular biologists, who seem determined to try to reduce everything about the human organism to “only” chemistry … Surely there are more levels of organization between human ethology and DNA than there are between DNA and quantum electrodynamics, and each level can require a whole new conceptual structure.
Anderson, perhaps unwittingly, is presenting a challenge to ecology. As scientists we are faced with the challenge of explaining and predicting change in very complex systems. ranging from natural ecosystems to completely artificial ecosystems of modern cities (such as Lima, seen below).
This is a hard challenge. After two centuries’ of ecology, we are just beginning to fully delineate the processes that work at each scale – piecing it together into a more coherent whole is still a major challenge. We may not yet even know how much we need to know, but I find it a worthwhile call to action for us all in the coming decades.
Anderson ends his article with an apocryphal conversation between two writers, which perhaps best illustrates the point he (and now I) are trying to convey:
Fitzgerald: The rich are different from us.
Hemingway: Yes, they have more money.
Summer is ending, and I’ve migrated back to Copenhagen for the rest of the year.
Being an ecologist, one of the first places I went to visit was the botanical garden and the university’s geological museum. I stumbled upon an exhibit of the Flora Danica – a guide to all the plants of Denmark, published under royal authority in 1761. The flora consists of thousands of engravings, each drawn carefully to help the reader identify the species from flowers, leaves, stems, and root. Color prints made from the engravings were distributed freely to bishops around the country, with other editions’ prices subsidized by the crown. It is a beautiful piece of work, but what struck me most was its complete lack of organization. Today, we have a robust system for organizing species, which we depend on heavily for a range of science and conservation applications. To me, seeing a book of plants without an organization scheme is like imaging a dictionary that isn’t published in alphabetical order. To understand why, we have to go back in time.
In the 1700s, taxonomy (the study of classification of organisms) was a new subject. Linnaeus published his famous Systema Naturae in 1735, but his ideas were by no means well-accepted immediately, nor was his approach based on arguments deeper than morphological similarity. As a result the Flora Danica, published a few decades later, was produced as an arbitrarily ordered set of color plates. Each publisher or book-binder could arrange these plates however they pleased. While charming, that system made it difficult to generalize and think more scientifically about plants. In fact, it was unclear that there should even be a correct way to organize species (why not group by poisonous and not-poisonous, for example) until the advent of evolutionary biology. Darwin showed that species arise from other species, providing a natural organization – more related species in the same groups, because they share the same evolutionary history. Gnetum, for example, looks passingly similar to Apocynum, but the groups are actually separated by tens of millions of years of evolution.
Modern cladistics, under Hennig, pushed the evolutionary idea forward and gave us the basis for our modern groupings of species.Below, you can see a small part of the botanist Alwyn Gentry’s monumental work, A Field Guide to the Families and Genera of Woody Plants of North west South America, giving the characters that help to separate different evolutionary groups of plants.
Illustrations have also changed – the lush detail of the Flora Danica is replaced by sparse line drawings, equally informative, but perhaps missing some indefinable romanticism of the earlier work.
Modern cladistics and molecular biology work – DNA sequencing, for example – have almost made it possible to know the full plant tree of life. You can see an evolutionary tree from one of the more recent studies (from 2010) below.
I think that in the next few decades the work of classifying all the plants of the world – and perhaps, all the known species – will be largely complete. We are riding a wave of advances in computer power and DNA sequencing methods that will build us a complete tree of life. Such a thing – a catalog and moreover an index to all the species that live – would surely be inconceivable to the royal botanists compiling a flora all those centuries ago.
The Colorado Rockies have an image as an unspoiled place – high mountains, dark forests, beautiful meadows. Such wild places are on the decline – as Sanderson et al. pointed out in 2002, the global human footprint continues to increase, leaving us only small fragments of ‘the last of the wild’. Ellis et al. (2010) have calculated that humans now use approximately 60% of all available land to support themselves, with the trend continuing to increase. So where does that leave places like the high peaks of the Rockies?
The answer is that they are not very wild, but parts are surprisingly becoming wilder. The peak above is Gothic Mountain, and at its base is the town of Gothic, home to the Rocky Mountain Biological Laboratory. The town now houses a seasonal population of approximately 100 people. But in the late 1800s, its population was more than 1000, perhaps several thousand. Mining claims dotted the landscape, with extensive deforestation and road-building supporting these operations. The Sylvanite Mine, for example, was five miles distant from Gothic and included “2,200 ft of tunnels; 1,200 ft of vertical workings and extensively stoped areas along the Sylvanite and Sylvanite No. 2 veins” according to a USGS report. Digging these tunnels, transporting ore, building structures for miners – the Colorado landscape of 1880 was a far more impacted place than 2013.
Remains of these mines still litter the landscape. Here is one abandoned adit on the south slope of Mt. Baldy, just an eight mile walk from Gothic.
Today, the ore is gone, the mines have long been unprofitable to operate, and the land has been converted to national forest. Wilder landscapes are returning. What we don’t yet understand is how long it will take, and how large the impacts have been. A recent study by Svenning and Sandel (2013) has shown that landscape change is often lagged, reflecting processes occurring hundreds to thousands of years ago. To put in a mine, to cut down a forest – these things are fast. But waiting for the land to forget these changes may be much slower.
The scene above is the Copper Creek drainage, near White Rock Mountain. Today it is in the Maroon Bells / Snowmass Wilderness – but the rock walls are dotted with tailings, collapsed shafts, wood pilings, and scattered metal fragments, reflecting a much different past. The last of the wild is not so easy to define after all.
Interaction networks can describe many interesting things – human social systems, like facebook, but also complex engineered systems like the internet, or animal societies. The past century has seen the development of an area of mathematics called graph theory, which can be used to describe the structure of these networks. There are statistics that describe how influential or connected different parts of the network are. More recently, models have been developed to explain the structure of these networks, resolving questions like why, for example, most nodes in a network have very few connections but a few tend to be very well-connected.
A key limitation to this kind of work is the fundamental assumption that a system can be described by a single, unchanging network. This is like assuming your circle of friends is static, or that an animal society never sees immigration or death. It’s clearly unrealistic, but capturing the dynamics of networks is surprisingly difficult. Many of our concepts simply don’t work when the system changes in time. The connectedness of a node may change over time – or a pathway of resource flow that looks strong in a static network may actually not exist during some time periods in a dynamic network. Developing new theory to account for these dynamic changes has been a long-standing challenge. There is much to be learned from dynamic networks, since nearly all phenomena of interest are actually dynamic – how networks come together and are taken apart, how persistent are certain structures, why some nodes -become- more important, and so on. Explanation is inherently a historical process, and history implies time.
We’ve recently published a paper surveying temporal dynamics in networks, but have also been thinking about the topic in an educational context. Many people have been interested in networks that are inspired by biology, but don’t have a strong background in animal societies.
We’ve therefore written a chapter for a new book, Temporal Networks, that focuses on temporal dynamics in social insect networks. The complex societies of ants and bees are a natural example of a network that changes in time in ways shaped by millions of years of adaptive evolution. Perhaps one can learn something from these systems, and apply some of the same ideas we use to study them in other contexts.
The book chapter surveys the basic biology of social insect networks, and shows several ways in which these societies can be understood in the context of network dynamics. The chapte also shows how task allocation in insect societies is actually quite variable over time, and has important consequences for the overall performance of a society.
Walk through the Rocky Mountains in the summer, and you will be immersed in a sea of green, and will hear the soft rustling sound of millions of leaves. These are quaking aspen (Populus tremuloides) trees, and they dominate the landscape. When I first came to Colorado in late-fall 2009, I was captivated by the beauty of these trees and wanted to learn more about them. Three years later, my first study of aspens has just been published.
One of the key mysteries in functional ecology is how plant leaves use carbon – there is a universal tradeoff between ‘fast’ leaves that have high photosynthesis rates, low carbon costs, and short lifespans, and ‘slow’ leaves that have low photosynthesis rates, high carbon costs, and long lifespans. Globally it appears that none of these strategies is better than others – all leaves seem to return approximately the same amount of carbon to the plant over the course of their life. So why the tradeoff, and what causes it?
I thought that leaf veins might hold the secret – they form the main structural support and water/carbon transport network for every species. Perhaps variation in the geometry of this network could lead to tradeoffs in leaf functioning that match what is seen worldwide. Moreover, I thought that since water flow in leaves is linked to the dryness of the environment, precipitation should control how many veins a leaf has. If this were true, then we would have a theory linking climate to leaf form to leaf function, and ultimately to the explanation of a global pattern.
Testing these ideas was a multi-step process. The first step was with pen and paper – developing equations to test. Second was fieldwork – exploring all over Colorado in search of plants from different environments. Aspen were a perfect study system, because they grow in large clones, where genes are invariant but environments change. Since the theory was about physiological change, I wanted to disentangle changes caused by environment from those caused by genetic variation.
So it was time to go find aspen clones all over Colorado, then measure their leaves. Fieldwork is always the best part of any project, and this one was no exception. On many aspen clones, leaves are out of reach, and trees have to be climbed. Here Neill Prohaska is exploring different ways to reach the canopy. If you’ve never climbed an aspen before, you should know that they have a powdery sort of bark that is very slippery and that makes climbing very difficult!
After two summers’ of fieldwork, all the data were in. It turns out that most of these ideas about vein networks are correct – they are linked to climate, and closely predict how plants use carbon. I got some of the math in the model wrong, but a revised version seems to make more robust predictions. We’re off to test the revision in the Peruvian Andes next!
Living in the Arizona desert, clouds are a rare occurrence. But in the Andean highlands, they are everything. The cloud forest (bosque nublado) that dominates these mountains can change its character rapidly, and so imposes its rhythms on its inhabitants.
The first thing to understand is where cloud forest comes from. Clouds form as moist air is heated by the sun and is pushed against mountainsides, forcing it to gain elevation. As the air rises, it begins to cool. As a result, the water vapor condenses and clouds appear.
The result is a band of clouds that persist at intermediate elevations on the sides of mountain ranges. These clouds can persist through the entire year, lending landscapes a dark gray appearance that is punctuated only by the occasional sunny day, brought about by abrupt temperature changes or ephemeral windy conditions. Living in these places is exactly like living inside of a cloud.
The constant presence of clouds means that moisture is always available to plants. The end result are ecosystems comprised of wet bogs and dark forests, rich in epiphytes like mosses and lichens, and dominated by soft soils and moisture-loving trees. Diversity is high in the cloud forest – some of the world’s highest levels of orchid and bird diversity are found in the Andean cloud forest. Climbing trees in these environments is a challenge – bark is often covered in layers of other organisms, and needs to be ‘shaved’ before attaching ropes.
The constant mist and frequent rain make for challenging work conditions. Expensive equipment has to be kept dry, and soils have to be preserved to prevent catastrophic erosion and the formation of muddy mires. Here you can see us setting up a large plastic tarp (special delivery from Cusco) to protect our drying ovens and gas analyzers. Rough as this looks, it was a notable improvement over the previous few days’ installation of the site, pushing a supply van through deep mud, huddling beneath a small clear plastic sheet in the cold rain, equipment bags piled beneath us, wondering where the cooking equipment and tents had been packed.
Clouds don’t remain in one place – they are always moving, changing from mist to rain. Sometimes they even behave like dense liquids. Here you can see a cloud that is denser than the surrounding air. It is being pushed across a valley and is slowly flowing down into another drainage, while the surrounding slopes remain sunny and dry. Clouds can also appear and disappear suddenly. On one off-trail descent into the cloud forest I was caught unawares by a building cloud and was within a few short minutes unable to see more than a few meters ahead of me. It was a very unnerving feeling of being utterly lost and without a sense of direction.
This cloud movement makes it possible to watch how a forest breathes. We work on the eastern edge of the Andes, thousands of meters above the Amazon basin. Each morning before sunrise, a sea of clouds appears over the Amazon. The moisture comes from evaporation from soils and transpiration from plants. Standing in the mountains, it feels almost possible to swim in this sea, floating just a little above the canopy of the forest. But as the day begins, transpiration increases, and so does the moisture in the air. And as the sunlight strikes the moist air, the clouds begin to rise.
Over the course of a few hours between sunrise and early morning, the clouds rise a thousand meters, shrouding the mountains in a thick gray layer. Wait some hours more, and transpiration slows down, the air begins to cool, and the clouds begin to retreat, exposing more and more of the mountainsides. Each day the forest breathes: a slow morning inhalation and a slower evening exhalation of moisture, transforming the landscape. It’s a magical experience to sit and watch a day pass from a high peak.
This daily dance of clouds brings moisture and life to the forest, but things are changing. As climates warm, the elevations at which clouds form are beginning to shift – and these shifts are occurring faster than plants and animals can keep up. The consequence is high mortality and turnover of species at low elevations that are now devoid of clouds, and invasion of high peaks by new species now shrouded in clouds. The future of Andean cloud forest is uncertain, as is the fate of the biodiversity hotspots it hosts. A new rhythm is coming to these places, and we are surely not ready for it.