University of Arizona, Tucson, Arizona USA

An ecologist wonders how biotic feedback matters to global-change research.

I have increasingly been drawn to the question of how the biotic world responds to climatic change. In the face of environmental change, biology responds — organisms often compensate, adapt and change the nature of their ecologies. But exactly how important is this biological feedback to how ecosystems respond to a warmer world?

My colleagues and I have called for a need to focus on quantifying the importance of what we call the three As — acclimation, adaptation and assembly — on ecosystem-level processes such as carbon flux.

Acclimation is a plastic response by an organism to a change in the environment, whereas adaptation is the end result of natural selection in populations. Assembly is how species come to dominate a local environment and is the result of ecological interactions. We know that all these processes are affected by changes in climate. The end result of the three As is a group of species that live in a given location and control the flow of resources and energy.

These processes operate on differing time scales and have mostly been studied in isolation. However, two fascinating papers (K. Ishikawa et al. New Phytol. 176, 356–364; 2007, and C. Campbell et al. New Phytol. 176, 375–389; 2007) assess the role of both acclimation processes and between-species adaptation in the responses of photosynthesis and respiration to changing temperature. Remarkably, they find that acclimation and adaptative responses seem to compensate for temperature-driven changes in carbon flux.

Putting these two As together with how species assemble in ecological communities will probably reveal generalities in how evolutionary biology and plant-community ecology matters in global change.

Posted by Brendan Maher at 07:29 PM | Permalink | Comments (1) | TrackBacks (0)

QUEST, University of Bristol, UK

A theoretical biologist suggests that evolution makes plants more predictable.

The debate over how forests respond to rising levels of carbon dioxide has brought home to me how much spin even a dry journal article can contain.

In the mid-1990s, when the forest Free Air Carbon dioxide Enrichment (FACE) experiments began, I thought that we were poised to learn how trees really respond to carbon dioxide. In these experiments, carbon dioxide is pumped over forests to simulate future conditions.

Unfortunately, years of data collection and scores of papers later, we still haven't reached agreement. Using the same data, researchers conclude that carbon dioxide either fertilizes forests or it doesn't (or the effect is small, or it goes away, or will soon go away...)

The situation would be helped if we had better theories of how trees might be expected to react to changes in their resources. It was refreshing, therefore, to encounter an elegant analysis of plant behaviour (O. Franklin New Phytol. doi:10.1111/j.1469-8137.2007.02063.x; 2007).

Plants, subject to selective pressure, have to optimize what they can. This is a basic principle of evolutionary biology, too often disregarded in experimental contexts.

Theoreticians have long known that an individual leaf in high carbon dioxide will maximize the amount of carbon it fixes — a measure of its growth success — if it lowers its nitrogen content to optimize the balance between photosynthesis and respiration.

Franklin extends this nitrogen optimization principle to the whole plant, a significantly more complex problem. His model predicts 83% of the variation in plant growth enhancement seen across FACE studies, explains the observed relationship between plant growth and canopy nitrogen content, and does much else besides. It is a welcome step forwards.

Posted by Jenny Hogan at 06:00 PM | Permalink | Comments (0) | TrackBacks (0)

Southern Methodist University, Dallas, Texas, USA

Fossils from ancient forests in Africa provide a palaeobotanist with insight into past climates.

I have spent many years collecting and studying fossil plants from regions in or near eastern Africa's rift valley, which runs southwards from Ethiopia to Kenya, and beyond.

These fossils provide evidence of ancient forests that once linked their living counterparts, the forests that today lie to the east and west of the rift. They also highlight past shifts in the region's climate, thought to be a driver of human evolution in the area, as grasslands became more common.

But were regional climatic changes mainly the result of changes in global climate? Or were they more to do with the development of the rift itself?

From Kenya's arid rift, I have studied 12.6-million-year-old fossils of Cola and Dioscorea (wild yam), plants that today grow side-by-side in much wetter African environments. The rift is an obvious culprit for drying here: the valley lies in the rain shadow of the rift's elevated margins.

More recently, my students and I have found much older examples of the same plant genera on the northwestern Ethiopian plateau, which has a long dry season.

The plateau is not in a rain shadow, but a recent modelling study (P. Sepulchre et al. Science 313, 1419–1423; 2006) surprised me by demonstrating that even moderate elevational changes could account for today's drier climate here, too.

It suggests that the high Ethiopian plateau acts as a barrier to incoming moist air masses, and need only have been 400–1,000 metres lower than today for the plants we found fossilized there to have flourished.

Other factors would surely have played an important part, but this work highlights palaeoaltitude as a significant driver of the region's climate.

Posted by Jenny Hogan at 06:00 PM | Permalink | Comments (0) | TrackBacks (0)

Liverpool John Moores University, UK

An ecologist enjoys a smelly experiment on a neglected link in the food web.

I have long been fascinated by an idea from the 1970s about rotting food. Daniel Janzen, now at the University of Pennsylvania in Philadelphia, suggested then that many of the noxious chemicals secreted by microbes in decaying food are produced to fend off large animals, allowing the microbes to keep the resource for themselves.

It's an intuitively appealing hypothesis. Our own experience is to be repulsed by putrid food, and several studies have shown that birds prefer fresh over rotted fruit. Most recently, a careful study in the seas off the southeasten United States provided further support for Janzen's idea (D. E. Burkepile et al. Ecology 87, 2821–2831; 2006).

In what must have been a gloriously smelly experiment, the researchers baited crab traps with dead fish, either rotten or fresh. The microbe-laden carrion was four times less likely to be consumed by scavengers than the fresh fish.

This provides clear evidence that microbes compete for food with larger animals, something that has been largely overlooked in the huge ecological literature on food webs and feeding relationships. But it doesn't tell us how the chemicals evolved.

Last year, I published with colleagues a theoretical analysis of the evolutionary implications of Janzen's idea (T. N. Sherratt et al. Ecol. Modell. 192, 618–626; 2006). Our model suggested that the chemicals cannot have evolved solely to protect against large animals, because the temptation for microbes to 'cheat' by free-riding on toxin production by others undermines the system.

The experiments done by Burkepile et al. show that the effect is real, but perhaps these chemicals first evolved for other reasons, such as inter-microbe competition?

Posted by Jenny Hogan at 06:00 PM | Permalink | Comments (2) | TrackBacks (0)

Stanford University, California

A palaeoceanographer worries not about corals, but about coral reefs.

To understand what the consequences of human-induced CO2 increases might be, I study how atmospheric CO2 concentrations fluctuated in the past.

One outcome of high atmospheric CO2 that is inevitable is ocean acidification. Atmospheric CO2 dissolves in sea water, lowering the pH of the ocean's surface layer.

We expect this to create problems for marine creatures that precipitate their skeletons from calcium carbonate, because the mineral dissolves in acid. Some researchers have suggested that scleractinian corals might even be driven to extinction.

But what does the geological record tell us? Corals' reef-building fossils have appeared and disappeared over the past 200 million years and despite periods of elevated atmospheric CO2, the organisms did not go extinct.

A recent experiment (M. Fine & D. Tchernov Science 315, 1811; 2007) resolves this apparent paradox. The team grew scleractinian corals for a year in sea water with a lower-than-normal pH. They found that the corals reproduced and grew happily in this acidic environment — albeit without their hard skeletons. The corals adjusted their skeleton-forming physiology in response to the different growing conditions.

So corals seem to be quite adaptable. But I would like to know whether other calcifying organisms have such physiological versatility.

Moreover, we have to remember that although corals may survive in an ocean with a lower pH as sea-anemone-like organisms, they are currently major contributors to the intricate physical structure of coral reefs. What will be the future of these ecosystems if their calcium-carbonate scaffolding disappears? Will our grandchildren enjoy the spectacular beauty of these 'rainforests' of the ocean?

Posted by Jenny Hogan at 06:00 PM | Permalink | Comments (0) | TrackBacks (0)

College of William and Mary, Gloucester Point, Virginia, USA

A marine scientist marvels at connections between the cold war and slimy mudflat worms.

Having grown up on the coast of New England, my childhood involved a good deal of digging around in the intertidal mud, unearthing things that most people of good sense do their best to avoid — things such as slimy, slithering worms, which often bite or smell bad, or both.

Older but no wiser, I was delighted to come across a recent paper (E. Teuten et al. Mar. Ecol. Prog. Ser. 324, 167–172; 2006) that has cleverly extracted a surprising scientific result from studies of such mudflat worms.

As well as reminding me of my dubious childhood pastime, the work recalls the period in which I grew up, during the cold war, when much of the world lived in fear of the nuclear weapons then being tested. This work takes advantage of one legacy of those tests.

The bomb tests sent into the atmosphere lots of the isotope carbon-14, normally present only at low levels. This bomb carbon-14 subsequently made its way into the oceans, where it became incorporated into plankton. The plankton in turn sank and became part of the coastal mud, providing a home and a food source for marine sedimentary animals.

Mudflat worms are generally believed to ingest wholesale the nondescript sediment in which they live, yet the worms examined in this study contained more bomb carbon-14 than the sediment surrounding them.

Thus, it seems that the worms assimilate from the amorphous goop, material that has been deposited since the cold war and so is younger than the average age of the sediment. Presumably, they do so because the newer material is more nutritious, but how they extract it is unknown.

Makes me want to get back out by the sea with my bucket.

Posted by Jenny Hogan at 06:00 PM | Permalink | Comments (0) | TrackBacks (0)

Max-Planck Institute for Biogeochemistry, Jena, Germany

A biogeochemist finds inspiration for life on the ocean floor.

My research interests lie in understanding the interplay between the physical and chemical conditions that constrain life, and the feedback processes by which life shapes the Earth's environment.

I want to understand these interactions in terms of a thermodynamic hypothesis that states that systems dissipate as much energy as possible. Can life be seen as an emergent outcome of this tendency for the whole Earth system? To test this, one would need to show that it is possible to predict the emergence of life from the hypothesis, as well as its impact on Earth's early environment.

Two articles (M. J. Russell & A. J. Hall GSA Memoir 198, 1–32; 2006, and M. J. Russell Am. Sci. 94, 32–39; 2006) could provide a starting point. The authors give a detailed picture of the thermodynamics of life emerging at hydrothermal mounds on the ocean floor.

One of the earliest metabolic reactions would have involved the conversion of hydrogen, carbon dioxide and sulphur compounds into organic carbon, acetate and water. This would have happened in the hot, mineral-rich spring water seeping into the hollow mound.

But its influence would have been felt more widely. Removing sulphur from the environment would have changed atmospheric composition and cloud cover, affecting the amount of sunlight reaching the ground. And acetate may have served as fuel for methanogens, methane-producing organisms known to live in vents. Increased methane production would have raised its levels in the atmosphere, resulting in higher surface temperatures on Earth.

Quantifying these interactions should help us to understand whether the evolution of our planet emerged from general thermodynamic trends.

Posted by Jenny Hogan at 06:00 PM | Permalink | Comments (1) | TrackBacks (0)

University of British Columbia, Vancouver, Canada

A marine biologist dives into the history of the Gulf of California.

A decade ago, I coined the term 'shifting baselines' to describe how society perceives environmental change. The concept has caught on: there's even a website, at http://www.shiftingbaseline.com, featuring short, explanatory films.

The films push the idea that the standards by which society assesses change are themselves changing. We tend to use the state of affairs that prevailed when we first became aware of an issue as our reference point for evaluating future change — a baseline that shifts with each generation.

A set of three brilliant papers illustrates how this can shape our understanding of ecosystems.

The most recent paper (A. Sáenz-Arroyo et al. Fish Fish. 7, 128–146; 2006) reconstructs from historical sources, such as pirates' logs, details of the Gulf of California's ecosystem stretching back to the sixteenth century. The researchers argue that the past abundance of creatures such as marine mammals, turtles and oysters recounted in these sources should be considered when setting conservation targets today.

Their previous work examined records of Gulf groupers, fish that once dominated the area's reefs (A. Sáenz-Arroyo et al. Fish Fish. 6, 121–133; 2005), concluding that fishery statistics didn't go back far enough to accurately map the species' decline.

Further, they quizzed three generations of artisanal fishers (A. Sáenz-Arroyo et al. Proc. R. Soc. Lond. B 272, 1957-1962; 2005), and found that fishers' knowledge of the location or habits of species disappeared within one generation, if the species became rare.

We are all affected by this kind of collective amnesia. It allows us to handle change. But it is also the reason why we accept losses that would be intolerable, were we aware of them.

Posted by Jenny Hogan at 06:00 PM | Permalink | Comments (0) | TrackBacks (0)

Scripps Institution of Oceanography, La Jolla, California, USA

A marine biologist sees the potential of cyanobacteria, and the benefits of their renaming.

Let's start with a false syllogism: bacteria are prokaryotes, blue-green algae are prokaryotes, and therefore blue-green algae are bacteria. All other algae are eukaryotes and so, the argument went, we should reclassify the Cyanophyta as cyanobacteria.

I was never in favour of this renaming, but it may have been good for funding. I've heard that grant applications for research on bacteria have better chances of success than those for research on blue-green algae.

And these oft-neglected organisms have a lot to offer. A recent paper on Lyngbya majuscula from Bill Gerwick, now at the Scripps Institution of Oceanography in La Jolla, California, and his colleagues (B. Han et al. J. Nat. Prod. 69, 572–575; 2006), for example, reveals some interesting new compounds.

L. majuscula grows on warm seashores as tufts, which, when they come loose and float away, can stick to swimmers' skin and cause a rash — known as swimmers' itch or seaweed dermatitis.

Gerwick and his team extracted from dried L. majuscula two compounds that may explain its irritant effect. The compounds, aurilide B and aurilide C, are hugely complicated ring-shaped molecules that resemble a toxin previously isolated from sea slugs.

In tissue culture assays, the compounds proved toxic to human and mouse cancer cells. Such natural products can act as starting points for pharmaceutical chemists.

Gerwick's paper refers to L. majuscula as a cyanobacterium in its title and as an alga elswhere in its text, but what's important is the science, not the names.

Posted by Jenny Hogan at 06:00 PM | Permalink | Comments (0) | TrackBacks (0)