Maternity leave (January 2023)
I (Anita) am slowly winding down virtual and in person meetings, to make a bit of room for an upcoming personal project: Baby#2. In my stead, Oli Hansen (oliver.hansen@eawag.ch) will be orchestrating a lot of project work in the group and can respond to many of your inquiries / requests on my behalf. I'll be back in action in June 2023.
I (Anita) am slowly winding down virtual and in person meetings, to make a bit of room for an upcoming personal project: Baby#2. In my stead, Oli Hansen (oliver.hansen@eawag.ch) will be orchestrating a lot of project work in the group and can respond to many of your inquiries / requests on my behalf. I'll be back in action in June 2023.
Two (!!) new papers out from Patrick’s PhD work (December 2022)
Before joining the Narwani lab as a postdoc, Patrick Thomas did a variety of research related to allelopathy in green algae, the importance of intraspecific variation in marine diatoms, and the role of phytoplankton food quality for consumers. Two papers were recently published detailing some of these results. One paper shows results from a meta-analysis aimed at testing the relative importance of different phytoplankton food quality factors (and their interactions) for zooplankton growth and reproduction: nitrogen, phosphorus, fatty acids, and sterols. In brief, the results show that all 4 types of nutrients can strongly inhibit zooplankton when they are limiting, that co-limitation by multiple nutrients is often significant, and that all of these effects depend on taxonomy, complexity of the experimental system, and more. Since the autotroph-consumer link is so important, this shows one way that increased prevalence of poor quality food (e.g. cyanobacteria) can have strong cascading effects on aquatic ecosystems.
The other new paper looks at plankton biodiversity from a completely different angle, specifically focusing on how understanding traits linked to algal chemical ecology could be useful for industrial-scale cultivation of algae for renewable bioproducts. The experiments in this paper show that green algae species can have very different sensitivities to certain allelopathic compounds (that algae themselves produce), and that growth of the focal species, Chlorella, is strongly correlated to excretion of these compounds, with both inhibitory and facilitative effects. This work could be important because using biodiverse assembled communities that suppress non-target species like grazers/competitors/pathogens (but not the target algae) could boost productivity/economic viability/sustainability of mass algae cultivation. This is closely related to Patrick’s current project on chemically-mediated interactions in natural and engineered phytoplankton communities, so stay tuned!
Before joining the Narwani lab as a postdoc, Patrick Thomas did a variety of research related to allelopathy in green algae, the importance of intraspecific variation in marine diatoms, and the role of phytoplankton food quality for consumers. Two papers were recently published detailing some of these results. One paper shows results from a meta-analysis aimed at testing the relative importance of different phytoplankton food quality factors (and their interactions) for zooplankton growth and reproduction: nitrogen, phosphorus, fatty acids, and sterols. In brief, the results show that all 4 types of nutrients can strongly inhibit zooplankton when they are limiting, that co-limitation by multiple nutrients is often significant, and that all of these effects depend on taxonomy, complexity of the experimental system, and more. Since the autotroph-consumer link is so important, this shows one way that increased prevalence of poor quality food (e.g. cyanobacteria) can have strong cascading effects on aquatic ecosystems.
The other new paper looks at plankton biodiversity from a completely different angle, specifically focusing on how understanding traits linked to algal chemical ecology could be useful for industrial-scale cultivation of algae for renewable bioproducts. The experiments in this paper show that green algae species can have very different sensitivities to certain allelopathic compounds (that algae themselves produce), and that growth of the focal species, Chlorella, is strongly correlated to excretion of these compounds, with both inhibitory and facilitative effects. This work could be important because using biodiverse assembled communities that suppress non-target species like grazers/competitors/pathogens (but not the target algae) could boost productivity/economic viability/sustainability of mass algae cultivation. This is closely related to Patrick’s current project on chemically-mediated interactions in natural and engineered phytoplankton communities, so stay tuned!
Paper out in Global Change Biology (December 2022)
With the rapid and multifarious environmental changes that are resulting from human activity, it has become urgent to develop methods to make predictions about how these environmental changes will affect communities, biodiversity and ecosystem functioning. Studies looking at "multiple stressors" are not uncommon, but often are rather simplistic: fitting statistical models to experimental data in which multiple stressors are manipulated in factorial experiments. Unfortunately, this does not characterize the nonlinearity of responses to individual environmental gradients, nor their interactive effects or how they may scale between different levels of biological organization. In this paper, we propose a more mechanistic method to understand and predict the impacts of multiple-drivers, with a particular focus on increasing temperature (or warming) as one of the drivers, and we apply it to consumer–resource dynamics.
So, what does the method entail?
The method involved first characterizing reaction norms of model parameters (e.g. growth rate or attack rate) to temperature in
the presence/absence of a second driver, e.g. resource limitation or acidification. Then, we use these reaction norms to parameterize a model of community or food-web dynamics. The modeled response can then be compared to data, allowing the model to be either validated, rejected or improved/refined. Ideally, once a good model is found and parameteterized, it can be used to make predictions and used as a decision-tool for practitioners and managers.
While the method itself can be very data-demanding, we also provide some suggestions about how to simplify this process and how to identify systems or questions for which it would be most feasible and useful.
With the rapid and multifarious environmental changes that are resulting from human activity, it has become urgent to develop methods to make predictions about how these environmental changes will affect communities, biodiversity and ecosystem functioning. Studies looking at "multiple stressors" are not uncommon, but often are rather simplistic: fitting statistical models to experimental data in which multiple stressors are manipulated in factorial experiments. Unfortunately, this does not characterize the nonlinearity of responses to individual environmental gradients, nor their interactive effects or how they may scale between different levels of biological organization. In this paper, we propose a more mechanistic method to understand and predict the impacts of multiple-drivers, with a particular focus on increasing temperature (or warming) as one of the drivers, and we apply it to consumer–resource dynamics.
So, what does the method entail?
The method involved first characterizing reaction norms of model parameters (e.g. growth rate or attack rate) to temperature in
the presence/absence of a second driver, e.g. resource limitation or acidification. Then, we use these reaction norms to parameterize a model of community or food-web dynamics. The modeled response can then be compared to data, allowing the model to be either validated, rejected or improved/refined. Ideally, once a good model is found and parameteterized, it can be used to make predictions and used as a decision-tool for practitioners and managers.
While the method itself can be very data-demanding, we also provide some suggestions about how to simplify this process and how to identify systems or questions for which it would be most feasible and useful.
Paper out in Ecology Letters (December 2022)
Global change studies are accumulating evidence that terrestrial and aquatic ecosystems often respond differently to the same human impacts. The reasons for these differences are unknown. In this paper, we suggest that the differences in the sensitivity of ecological communities to human impacts may be explained by differences in the relative importance of four fundamental processes of community ecology which are responsible for driving biodiversity dynamics. We use the example of how climate change, and warming in particular, is expected to have different impacts in freshwater and terrestrial systems. Specifically, we propose a mechanistic approach for systematically understanding (and potentially predicting) these differing impacts of global change drivers by leveraging the theory of ecological communities proposed by Mark Vellend. We reviewed the literature to summarize our current understanding of (i) how the four fundamental processes of community ecology appear to differ between terrestrial and freshwater systems, and (ii) how the differences we observe may lead to divergent responses to human impacts across ecosystems.
This was a large and unique collaborative synthesis project between biodiversity researchers housed at two Swiss Federal Institutes: Eawag and WSL. It was funded by the 2020 Blue Green Biodiversity Initiative of the ETH Domain.
Global change studies are accumulating evidence that terrestrial and aquatic ecosystems often respond differently to the same human impacts. The reasons for these differences are unknown. In this paper, we suggest that the differences in the sensitivity of ecological communities to human impacts may be explained by differences in the relative importance of four fundamental processes of community ecology which are responsible for driving biodiversity dynamics. We use the example of how climate change, and warming in particular, is expected to have different impacts in freshwater and terrestrial systems. Specifically, we propose a mechanistic approach for systematically understanding (and potentially predicting) these differing impacts of global change drivers by leveraging the theory of ecological communities proposed by Mark Vellend. We reviewed the literature to summarize our current understanding of (i) how the four fundamental processes of community ecology appear to differ between terrestrial and freshwater systems, and (ii) how the differences we observe may lead to divergent responses to human impacts across ecosystems.
This was a large and unique collaborative synthesis project between biodiversity researchers housed at two Swiss Federal Institutes: Eawag and WSL. It was funded by the 2020 Blue Green Biodiversity Initiative of the ETH Domain.
Paper out in Ecology Letters
(September 2022)
Who will win in a competition for resources? This is an old question but predictive frameworks to answer it are scarce, and those that exist have only been shown to be useful in very controlled environments and simple communities. In this paper we aim to test the utility of Tilman's Resource Competition Theory in making predictions of species' competitive success outside of highly controlled environments and simplified communities. We ran outdoor mesocosm experiments to do this, and tested the theory in complex, natural phytoplankton communities. We verify the utility of this trait-based predictive framework AND we show that species minimum resource requirements (R*s) evolve! This represents a heroic amount of empirical work by Dr. Irene Gallego, who ran in-lake and rooftop mesocosm experiments, isolated strains of algae before and after selection, and then measured their R*s in the lab, all during the Covid 19 pandemic years. Bravo Irene!
(September 2022)
Who will win in a competition for resources? This is an old question but predictive frameworks to answer it are scarce, and those that exist have only been shown to be useful in very controlled environments and simple communities. In this paper we aim to test the utility of Tilman's Resource Competition Theory in making predictions of species' competitive success outside of highly controlled environments and simplified communities. We ran outdoor mesocosm experiments to do this, and tested the theory in complex, natural phytoplankton communities. We verify the utility of this trait-based predictive framework AND we show that species minimum resource requirements (R*s) evolve! This represents a heroic amount of empirical work by Dr. Irene Gallego, who ran in-lake and rooftop mesocosm experiments, isolated strains of algae before and after selection, and then measured their R*s in the lab, all during the Covid 19 pandemic years. Bravo Irene!
Paper out in the Proceedings of the National Academy of Sciences (August 22, 2022)
Back in 2017, we began some conversations speculating about how common tipping points are in lakes around the world. It's been long road, but today our paper came out in PNAS presenting a first attempt to answer to this question. We used estimates of the productivity of 1,015 lakes from satellite imagery to evaluate how lake productivity has changed over time across the globe. We found that 12.8% of the world's large lakes show evidence of regime shifts which we could call "candidate tipping points". The number of lakes "tipping" to more productive states is increasing over time. Human population density within a watershed was a significant predictor of the probability of a lake experiencing a tipping point. However, the probability decreases with the wealth of the human population (GDP) - emphasizing inequality in access to stable freshwater resources. This was a very fun, cross-institutional, cross-disciplinary project. Thank you to Luis Gilarranz, Daniel Odermatt, Rosi Siber and Vasilis Dakos for the great interactions and zoom calls full of laughs.
Back in 2017, we began some conversations speculating about how common tipping points are in lakes around the world. It's been long road, but today our paper came out in PNAS presenting a first attempt to answer to this question. We used estimates of the productivity of 1,015 lakes from satellite imagery to evaluate how lake productivity has changed over time across the globe. We found that 12.8% of the world's large lakes show evidence of regime shifts which we could call "candidate tipping points". The number of lakes "tipping" to more productive states is increasing over time. Human population density within a watershed was a significant predictor of the probability of a lake experiencing a tipping point. However, the probability decreases with the wealth of the human population (GDP) - emphasizing inequality in access to stable freshwater resources. This was a very fun, cross-institutional, cross-disciplinary project. Thank you to Luis Gilarranz, Daniel Odermatt, Rosi Siber and Vasilis Dakos for the great interactions and zoom calls full of laughs.
Vanessa Weber de Melo gets interviewed by aspiring science journalist, Sofia van Moorsel (February 25, 2022)
Vanessa explains clearly why understanding how phytoplankton respond to warming and resource limitation at the metabolic level may help us fundamentally understand links between cellular stress and higher-level responses: for example which populations will survive and how will biodiversity be affected. The description of her work was published in the Zürcher Oberländer and the Glattaler (text in German - click to see the articles). Exciting, Vanessa and Sofia!
Vanessa explains clearly why understanding how phytoplankton respond to warming and resource limitation at the metabolic level may help us fundamentally understand links between cellular stress and higher-level responses: for example which populations will survive and how will biodiversity be affected. The description of her work was published in the Zürcher Oberländer and the Glattaler (text in German - click to see the articles). Exciting, Vanessa and Sofia!
Congratulations, Irene! (May 2021)
Irene Gallego received a 5 month Academic Transition Grant from Eawag to work on single-cell trait variation among phytoplankton taxa under resource limitation using high-throughput imaging. That means Irene will be sticking around with us for a while longer. We are so happy and proud of you, Irene.
Irene Gallego received a 5 month Academic Transition Grant from Eawag to work on single-cell trait variation among phytoplankton taxa under resource limitation using high-throughput imaging. That means Irene will be sticking around with us for a while longer. We are so happy and proud of you, Irene.
Welcome to the group!
Shannon Eckhardt, Lisa Marchand, Clara Fronda and Gabriella Mege are joining us this summer (2021).
Shannon joins us as a scientific assistant after completing her internship in the group early in the spring. Lisa and Clara are doing internships in the group this summer and will be working with Vanessa on phytoplankton metabolomics. Gabriella accepted a 3-year scientific assistant position in the group and will be working on the SNF-Funded project investigating the influence of temperature on competition in freshwater phytoplankton. Welcome everyone - we are so glad to have you join us.
Paper out in Ecology: Non-additive effects of foundation species determine the response of aquatic ecosystems to nutrient perturbation (May 2021).Eutrophication acts as a disturbance to aquatic ecosystems. Foundation species, or those species that are crucial in structuring communities and the functioning of ecosystems, are likely to be important for the resilience in the face of disturbance as well. We used outdoor experimental pond ecosystems to manipulate the presence of two foundation species, the macrophyte Myriophyllum spicatum and the mussel Dreissena polymorpha. We quantified ecosystem responses to multiple nutrient disturbances over two years. We used high-frequency measurements (every 15 min) from automated sondes to model whole-ecosystem metabolism, and to measure multiple ecosystems properties. Overall, both foundation species strongly affected the ecosystem responses to nutrient perturbation and initially suppressed the increase in phytoplankton abundance following nutrient additions. However, when both species were present, phytoplankton biomass increased substantially relative to other treatment combinations. The response was non-additive for multiple ecosystem metrics following the nutrient perturbations in both years. We demonstrate how interactions between foundation species can cause strong deviations from the expected responses of aquatic ecosystems to nutrient additions.
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Welcome to the group, Imran Khaliq (Jan 2021).
Imran is the BGB postdoc working on an ETH-Domain funded project on warming-related community turnover. He moved to Switzerland in March and is doing a fantastic job of wrangling enormous amounts of biodiversity, body size and thermal niche data.
Imran is the BGB postdoc working on an ETH-Domain funded project on warming-related community turnover. He moved to Switzerland in March and is doing a fantastic job of wrangling enormous amounts of biodiversity, body size and thermal niche data.
Paper out in Philosophical Transactions of the Royal Society B:
The evolution of competitive ability for essential resources (March 2020).
Competition and resource limitation are important determinants of biodiversity and community structure. However, competitive abilites are normally treated as fixed in models and empirical investigations of competition. In this paper we show that minimum resource requirements (R*) and other traits related to competition can evolve in response to selection under essential resource limitation. Our findings suggest that competition is a moving target, and ecological models of competitive community assembly should incoporate the potential for evolutionary change in competitive abilites. Surprisingly however, we did not find evidence supporting the widely held notion that an improved ability to compete for one resource should come at the cost of a loss of competitive ability for another. In fact, improvements in competitive ability were often positively associated. We did find support for a 'gleaner-opportunist' trade-off however, suggesting that one can either grow fast in replete environments or win in resource-limited environments, but not both. Read the full article and the other great papers that make up a part of this special issue of Phil Trans here.
The evolution of competitive ability for essential resources (March 2020).
Competition and resource limitation are important determinants of biodiversity and community structure. However, competitive abilites are normally treated as fixed in models and empirical investigations of competition. In this paper we show that minimum resource requirements (R*) and other traits related to competition can evolve in response to selection under essential resource limitation. Our findings suggest that competition is a moving target, and ecological models of competitive community assembly should incoporate the potential for evolutionary change in competitive abilites. Surprisingly however, we did not find evidence supporting the widely held notion that an improved ability to compete for one resource should come at the cost of a loss of competitive ability for another. In fact, improvements in competitive ability were often positively associated. We did find support for a 'gleaner-opportunist' trade-off however, suggesting that one can either grow fast in replete environments or win in resource-limited environments, but not both. Read the full article and the other great papers that make up a part of this special issue of Phil Trans here.
Paper out in Oecologia: Warming and Biodiversity drive CO2 dynamics in freshwaters (January 2020)
Climate change and biodiversity losses are occuring simulaneously around the world. Though we know that each of these changes can influence the properties and functioning of ecosytems, little is known about how they may interact, and how their effects on ecosystem properties may be driven by restructuring of communities. In this mesocosm experiment using freshwater foodwebs, we manipulated both phytoplankton species diversity and temperature, and investigated the influence of these factors on community structure, total phytoplankton biomass, and the dissolved concentrations of CO2. We found that while there were no interactive effects of warming and diversity on the CO2 concentrations of the water, each factor alone had substantial negative effects, with these effects being largely mediated by positive effects on total phytoplankton biomass. You can read the full article here.
Climate change and biodiversity losses are occuring simulaneously around the world. Though we know that each of these changes can influence the properties and functioning of ecosytems, little is known about how they may interact, and how their effects on ecosystem properties may be driven by restructuring of communities. In this mesocosm experiment using freshwater foodwebs, we manipulated both phytoplankton species diversity and temperature, and investigated the influence of these factors on community structure, total phytoplankton biomass, and the dissolved concentrations of CO2. We found that while there were no interactive effects of warming and diversity on the CO2 concentrations of the water, each factor alone had substantial negative effects, with these effects being largely mediated by positive effects on total phytoplankton biomass. You can read the full article here.
Paper out in Proceedings of the Royal Society B
(October 16, 2019)
We performed whole-pond experimental manipulations to investigate how foundation species and their interactions can affect the functioning and stability of aquatic ecosystems in response to disturbance by nutrient inputs. We found that while each species alone was able to reduce the extent of algal blooms and keep the water clearer over time, this effect was reversed when both species occured together. In the presence of both foundation species, the sytems became turbid and recovered more slowly from larger and larger nutrient additions. This change in system behavior was associated with an increase in dominance by a small cyanobacterium - Synechococcus - and a drop in multivariate trait evenness. In turn, numerous chemical and physical properties of the systems also changed. To find out more, take a look here.
photo credit: Thomas Klaper
(October 16, 2019)
We performed whole-pond experimental manipulations to investigate how foundation species and their interactions can affect the functioning and stability of aquatic ecosystems in response to disturbance by nutrient inputs. We found that while each species alone was able to reduce the extent of algal blooms and keep the water clearer over time, this effect was reversed when both species occured together. In the presence of both foundation species, the sytems became turbid and recovered more slowly from larger and larger nutrient additions. This change in system behavior was associated with an increase in dominance by a small cyanobacterium - Synechococcus - and a drop in multivariate trait evenness. In turn, numerous chemical and physical properties of the systems also changed. To find out more, take a look here.
photo credit: Thomas Klaper
Mesocosms and more (April 24, 2019)
Setting up in-lake mesocosms
We are preparing for in-lake mesocosm experiments this summer, and there is a lot inolved.
Last week we went on a deep-lake dive with the Lake Greifen police. We played a game of hide and seek with our missing mesocosm buoy. The Lake Policeman was very kind and offered to put on his dry-suit to do his detective work. Lucky for us, X marked the right spot and he managed to retrieve the sunken buoy and anchors within a few hours.
We also had a great visit to Seeon, to visit Mia Stockenreiter. Mia gave us all the details on how to get mesocosms set up in lakes: from heat-sealing polyethylene bags, to scaring off birds. With her wise tips, we are ready to meet the challenge of manipulating resource availability in Lake Greifen.
Setting up in-lake mesocosms
We are preparing for in-lake mesocosm experiments this summer, and there is a lot inolved.
Last week we went on a deep-lake dive with the Lake Greifen police. We played a game of hide and seek with our missing mesocosm buoy. The Lake Policeman was very kind and offered to put on his dry-suit to do his detective work. Lucky for us, X marked the right spot and he managed to retrieve the sunken buoy and anchors within a few hours.
We also had a great visit to Seeon, to visit Mia Stockenreiter. Mia gave us all the details on how to get mesocosms set up in lakes: from heat-sealing polyethylene bags, to scaring off birds. With her wise tips, we are ready to meet the challenge of manipulating resource availability in Lake Greifen.
Paper in press at Oikos (March 26, 2019)
Temperature‐dependence of minimum resource requirements alters competitive hierarchies in phytoplankton
In this paper we measured the minimum resource requirements for light and nitrogen of six different phytoplankton species along a gradient of temperatures. We found that temperature can alter resource requirements and, as a result, shift competitive hierarchies for resources. Check it out!
Temperature‐dependence of minimum resource requirements alters competitive hierarchies in phytoplankton
In this paper we measured the minimum resource requirements for light and nitrogen of six different phytoplankton species along a gradient of temperatures. We found that temperature can alter resource requirements and, as a result, shift competitive hierarchies for resources. Check it out!
ChlamEE P* experiments up and running (March 21, 2019)
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The set-up of the last R* experiment to investigate how competitive abilities of Chlamydomonas reinhardtii evolve under long-term resource limitation is off to the races!
Hats off to this amazing, hard-working team. They may have broken a record on the number of people working simultaneously in a sterile hood. |
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Welcoming new folks to the group! (March 1, 2019)
Carolina Carvalho joins us today as a scientific assistant. She'll be a crucial member of our team as we run lake-mesocosm and lab evolution experiments this summer. Welcome Carolina!
Irene Gallego-Nogales will also join the group in April. Irene will be working on an SNF-funded postdoc in April to investigate the evolution of competitive ability in phytoplankton in natural communities. Irene joins us from Bas Ibeling's group at the University of Geneva, where she had been investigating the role of cell size in shaping niche and fitness differences that determine coexistence in phytoplankton. Check out her paper in the ISME J!
Irene Gallego-Nogales will also join the group in April. Irene will be working on an SNF-funded postdoc in April to investigate the evolution of competitive ability in phytoplankton in natural communities. Irene joins us from Bas Ibeling's group at the University of Geneva, where she had been investigating the role of cell size in shaping niche and fitness differences that determine coexistence in phytoplankton. Check out her paper in the ISME J!
Paper out in Nature Communications! (November 7, 2018)Proteome evolution under non-substitutable resource limitation
Our paper on the evoluiton of protein expression under long-term selection by resource limiation is out in Nature Communications. Also, check out the associated "Behind the paper" blogpost in Nature Ecology and Evolution. Take a look! |
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