Easy-Going Plankton

The importance of phytoplankton in the global carbon cycle seems to be gaining recognition resulting in many studies being performed to better understand factors that affect the size and productivity of phytoplankton communities. This trend is not surprising as the need to sequester carbon is only increasing. Anthropogenic effects continue to raise the level of carbon dioxide in the atmosphere year by year, in fact global CO₂ hit a multi-million year high of 398.35 parts per million in April this year (up from 396.45ppm in 2012), and exceeded 400ppm for the first time in recorded history, on the 9^th of May. With this in mind it is clear that an understanding of the organisms responsible for nearly half of global primary productivity is paramount. Primary productivity, in this case, is the production of organic compounds from CO₂ through the process of photosynthesis. The modelling of phytoplankton communities is of interest to me as I will be building a phytoplankton biomass model as one of my honours projects. Many of the processes determining the growth and life cycle of these organisms are well understood through decades of empirical research, and the extension into mathematical modelling is allowing for fascinating predictions and insights into the future of the marine environment.

Phytoplankton are at the bottom of the oceans very complicated food web and can be thought of as micro-plants of the ocean which absorb CO₂ through the process of photosynthesis. The productivity of this reaction is dependent on nutrient concentrations and environmental conditions such as light availability, mixed layer depth and temperature. Temperature plays an important role in marine and estuarine systems as it affects water stratification, most current work involves the modelling of this relationship. A recent paper by Thomas et al (2012), titled “A global Pattern of Thermal Adaption in MarinePhytoplankton” published in Science magazine, investigates the direct impact of temperature on marine phytoplankton. The authors point out that not only is phytoplankton sensitive to temperature, but this sensitivity is skewed, with higher temperatures having significantly worse consequences for many phytoplankton species. With global ocean temperatures set to rise, the future of phytoplankton appears rather dark. Given that a large portion of global atmospheric carbon is sequestered by phytoplankton, it is useful to understand how predicted changes in ocean water temperatures will affect the productivity and community structure of phytoplankton populations.

In order to understand how ocean warming will affect phytoplankton productivity and distribution the authors attempted to understand the current relationships between productivity and temperature and the global distribution of phytoplankton. The analysis of 194 strains of phytoplankton from information gleamed from over 80 publications from 1935 - 2011 revealed a strong trend in the latitudinal distribution of phytoplankton and the optimum temperature for productivity (the authors sneakily point out that this suggests a global trend in a microbial trait, which is currently unidentified). An even stronger trend between that optimum and the mean annual temperature at the population’s location was found. This suggests that phytoplankton populations are highly adapted to local temperatures.  Interestingly polar and temperate optimum temperatures were found to be higher than the annual temperatures at these points, which got me thinking, if oceanic temperatures are set to rise (which models predict to be the case in many regions) then surely phytoplankton with optima above current average temperatures will thrive? Unfortunately the predicted overall increase in temperature is not globally uniform and some regions around the poles and temperate regions are expected to remain constant and even possibly decrease.

The collaboration between optimum temperatures and location was not enough for the authors to confirm an adaptive relationship (one where strains possess the characteristics they do as a result of their environment) and so an eco-evolutionary model was run on the strains of phytoplankton in question. The model worked by “forcing” differences in strains of phytoplankton to be the same so that only temperature tolerance could be compared, essentially simplifying the system enough that the strains are comparable. For each location the optimum temperature was allowed to evolve, based on an evolutionary algorithm. This gives an output of the best strategy at each location based on temperature tolerance. The results showed that optimum temperature for phytoplankton primary production should in fact increase with increasing local mean temperatures. I consider this result great news for phytoplankton, as it indicates that they are in fact able to adapt to changes in temperature. However there is no current understanding of the rate at which strains are able to adapt to changing temperatures.

The paper goes on to a species distribution model which matches the current requirements of phytoplankton communities with the predicted available environments for 2091-2100. From this point of view large decreases in diversity are expected as regions become more or less favourable, with a dominant shift pole-ward for most species and a drastic decrease in diversity at the tropics. Without an understanding of the rate at which phytoplankton can adapt to environmental conditions, a species distribution model seems unimportant. Most biologists will agree that high diversity is an imperative characteristic of a healthy ecosystem and in this regard the movement of plankton strains is of interest, however these predictions carry little weight when it is known that phytoplankton are able to adapt to changing temperatures, additionally, given their rapid rate of reproduction and short lifespan, they are increasingly likely to evolve under strong temperature pressures. What would be of greater interest to me would be if the increasing temperatures where likely to lead to decreased population sizes, and not just decreased diversity.

Halfway There

In high school I was introduced to the concept of “global warming”; the idea that the lifestyle I had been living was causing harmful, irreversible change to the environment shocked me and redirected my life immediately. Since then the term has lost some of its credibility and has subsequently been replaced by “global climate change” mostly, in my opinion, to remove ammunition from the sceptics proclaiming that a longer summer and less harsh winter might be quite enjoyable. In the last 8 years the term has adapted in my life and been subdivided into multiple categories which all come down to “anthropogenic effects”. With this term I encompass (to name a few) habitat fragmentation, loss of biodiversity and perhaps most importantly, urbanisation. All three of these concepts are dealt with in this month’s chosen article: “Global forecasts of urbanexpansion to 2030 and direct impacts on biodiversity and carbon pools” by Seto, Güneralp and Hutyra (2012). As an “environmentalist” (read: person aware of the severity of the situation facing humans today) my biggest problem is trying to get my peers to understand that nothing is localised, that everything has an impact and that our actions are affecting the world in a temporally specific manner. This article is the latest weapon in my arsenal.

A large part of being informed about the severity of the global situation is feeling an obligation to educate those who don’t, and within that to work towards mitigating the problems. I see this paper as vital movement towards quantifying the possible path our civilisation is on. The fact that most people see urbanisation as a localised issue is one that sits with me daily and is a major tenant of the article. The world is getting smaller and smaller every day and our ability to mark the planet is increasing exponentially. This article makes the point that in one generation we will possibly globally urbanise land the equivalent size of South Africa. That is, there is a probability greater than 75% that 1,2 million square kilometres of land will be expanded into. Although the authors do not go into great detail about the methods they used to calculate these probabilities, they do explain that a probabilistic model was created using global land cover from 2000, urban population projections and gross domestic profit, and that five sources were used to create the model. As someone who enjoys mathematics, statistics and models, I would have liked more information about the workings of the model but the paper speaks loud enough to drown out my worries about fairly calculated probabilities.

I understand that with an increasing population, urbanisation is, to some extent, inevitable; but is it too much to ask that that expansion be efficient? The authors point out that urban area is expanding on average twice as fast as urban populations are. The denialist retort in this case could be that if space is a limited resource, at some point we will reach a sort of “equilibrium”, and that reaching that “equilibrium” is inevitable so it doesn't matter if it happens now or 50 years from now. Although this might be true it is our job as “environmentalists” to point out that every expansion has a cost to biodiversity and ecosystem services. Ecosystem services include the systems that allow us to have clean water, food, a stable climate and crop pollination, and biodiversity plays a role in many of these systems. As human populations grow, demand on these systems increase and it is vital that they are conserved. For this reason the authors include a study of the overlap of areas with a high probability of expansion and global biodiversity hotspots. To localise the point, one of the mentioned biodiversity hotspots is the Cape Floristic region which has a 75% or greater chance of losing 1100 square kilometres to urbanisation by 2030. Overall urbanisation of biodiversity hotspots is expected to increase by 160% from 2000 to 2030 with some areas, such as The Eastern Afromontane, the Guinean Forests of West Africa, and the Western Ghats and Sri Lanka hotspots experiencing increases of urbanisation of between 900% and 1900%. Not only are these regions associated with biodiversity but they additionally act as large carbon stores and the authors dedicate a section of the paper to the impacts that expansion will have on carbon pools. So, not only will the inevitable expansion impact biodiversity, but it could act to increase levels of carbon in the atmosphere (a known driver of climate change). To bring the point home just a little more the authors include an analysis of the endangered and critically endangered animals which occur in the regions likely to be urban by 2030. It is important to note that the paper does not take into account the additional pressures and indirect impact that this expansion could have and as such can be considered a conservative assessment of the situation.

Reading this paper has opened my eyes to the importance of global scale realistic forecasts that explicitly deal with human driven changes. I believe the biggest problem with it could be that the information will reach so few non-environmentalists. Perhaps this blog can work to fix that. Whatever stance you choose to take on politics, religion, social organisation or climate change, the problem of anthropogenic effects on the environment is one that faces us all. The world is smaller than we think and our ability to affect its composition is growing every day. The authors suggest that we look to Aldo Leopold (A 19th century ecologist who developed a set of land ethics) and Sir Alex Gordon (a forward thinking British architect) for guidance in policy making and design, considering development that allows for future changes and moves to sustainable practices. I would include that space-use efficiency and optimisation are of the utmost importance in urban land-use, agriculture, and ecosystem service conservation. As the authors direct you to Leopold and Gordon I add a direction to the concept of biomimicry and the words of Janine Benyus “Anything that we design—a product, a process, or a policy--has to ultimately pass muster in the biological realm. It has to help us thrive, but it also has to keep the habitat intact for our successors. A robin building a nest and an architect building a building should have the same concern: “How will the chicks fare here?”

Reference
Seto K. C., Güneralp B., and Hutyra L. R. (2012) Global forecasts of urban expansion to 2030 and direct impacts on biodiversity and carbon pools. Proceedings of the National Academy of Sciences 109: 16083‐8.

Panchreston

For my first blog post I chose an article, actually a letter, from the highly acclaimed journal Nature. Nature is a multidisciplinary journal and it is very easy to get lost in the land of science when reading the titles of the articles in each edition. Luckily my brain is tuned to search out phrases like “human disturbance” and “diversity loss” and I quickly found this letter written by A. S. MacDougall with input from R. Turkington, K. S. McCann and G. Gellner titled ‘Diversity loss with persistent human disturbance increases vulnerability to ecosystem collapse’. Any young ecologist would find it difficult to not at least read the abstract. Upon doing so, I learned that the authors embarked on a 10 year experiment aimed at finding empirical evidence that a combination of environmental change and a loss in diversity increases the risk of an ecosystem collapse. My interest was piqued.


In my modest look into the world of ecology I have stumbled across multiple instances where a team of researchers focuses on a question that is easy to answer with a vague reference to some aspect of ecology that is difficult to test but important to assume. In many cases this leads to a necessity for generalisations and perhaps even a picking-and-choosing of relevant information, irrespective of context. These aspects usually involve a host of, in my opinion, vague references. Ecologists, and perhaps all natural scientists, are constantly being forced to build a world on assumptions and uncertainties in order to make one aspect of our understanding of complex systems more certain. The search for answers, and certainty, is why we do what we do. MacDougall et al state that theory predicts that a combination of environmental change and diversity loss increase the risk of abrupt and potentially irreversible ecosystem collapse. The letter cites six papers supposedly deal with this.


Ives and Carpenter (2007), Hooper et al. (2012) Loreau (2010), Barnosky et al. (2012), Kéfi et al. (2007), and Rietkerk et al. (2004) deal with a many aspects of the theory with some small scale empirical studies, and many commentaries on the state of the ecosystems but little comment based on in situ observations of ecosystem collapse as a result of environmental change or biodiversity loss. This is where MacDougall et al really grabbed my attention. Conducting a 10 year experiment of this nature is no mean feat and the results that this experiment yields are on a scale that surpasses most of those mentioned in the literature. All the models in the world are useless without experiments such as these.


There is no doubt that the results of the experiment are interesting. The finding that a negative relationship between diversity and function exist, begs me to ask, what we are actually conserving for? I often find myself wondering what humans are conserving for. Are we conserving out of nostalgia and fear of change or are we conserving our environment in order to better sustain ourselves? Where is the line dividing us from our environment? I grew up on the Gauteng Highveld surrounded by grassland and a large portion of my undergraduate studies dealt with fire regimes in Savanna and Grassland ecosystems. I find the idea of managing with fire interesting as the line dividing humans from being a part of the ecosystem to managers of the ecosystem becomes examinable. MacDougall et al examined the relationship between an altered and diversity poor ecosystem and vulnerability to collapse in degraded but species rich pyrogenic grassland; however, I did not find that the letter set the information into any real world context. The main findings of this experiment verified the theory that biodiversity is functionally significant in pyrogenic ecosystems, as grasslands with greater native species diversity were able to resist woodland invasion after a fire. While the monoculture low diversity areas were unable to stand up to the harsh introduction of a fire regime.

Although the article verifies some very important theory about managing grassland with fire, I felt that many aspects of the bigger questions were left out of the paper. The main benefit that I believe I received from this paper is contemplation into the roles we as humans play in our environment. The diversity-stability debate was not one I had considered before and it will possibly shape many of the conclusions I draw when debating conservation issues. I find myself led on to ask more and more questions about the need to conserve biodiversity and the search for mechanistic evidence that the processes we believe to be important are indeed playing the role in the ecosystem that we believe that they are.


One of my honours projects will be focusing on the connectivity of a landscape. The fundamental idea behind connectivity conservation is that in a fragmented landscape a higher level of connectivity allows for survival of metapopulations. My project will tend towards an analysis of scale and measures of connectivity with my faith being placed on the ideas of those before me, mainly that connectivity has importance. I am embarking on this study with the hope that what I find will be of interest to the community and will benefit the science, but generalisations and assumptions will need to be made. The link between metapopulation survival, connectivity and overall survival is mostly a theoretical one, rarely empirically studied. Perhaps real world investigations are too risky and in that regard I commend MacDougall et al. In the end not every question can be answered by any given study and in systems as complex as those found in nature assumptions will always be necessary. As I am beginning my journey into research biology this is an important lesson to learn in order to avoid feeling overwhelmed by the vastness of the unknown. I may have to build my questions on shaky theories and uncertainties, and I may not be able to solve all of the world’s problems, but, like MacDougall et al. perhaps I can shed some light on some cracks and add a measure of certainty so that



Reference

MacDougall A. S., K. S. McCann, G. Gellner, and R. Turkington, 2012. Diversity loss with persistent human disturbance increases vulnerability to ecosystem collapse. Nature 494: 86–89



pan·chres·ton [pan-kres-tuhn]:

noun a proposed explanation intended to address a complex problem by trying to account for all possible contingencies but typically proving to be too broadly conceived and therefore oversimplified to be of any practical use.

Modules and Models 101

This blog will serve two purposes:

1. To broaden my knowledge of current work in biological fields, including ecology and zoology
2. As an assessment tool to develop my research and writing skills.

These two aims should improve my skills during my honours year at UCT.

I am required to write blogs based on articles published in
Nature
Proceedings of the National Academy of Sciences, USA
Science
Trends in Ecology and Evolution

Although I still do not know what the year holds, I am sure that the content of this blog will be educational and developmental for me, and hopefully interesting for the reader.

I am required to blog a minimum of once a month but I may intersperse these obligatory posts with updates on my modules, projects and ancillary developments along the way.

I hope you enjoy the ride

Kiki