1,721,083 research outputs found
Ward-Ecology/Plankton_IBM: Plankton_IBM post review EL
No full textUpdated code giving more detailed instructions on how to run simulations and reproduce figures in Ward &amp; Collins</span
Mixotroph ecology: More than the sum of its parts
No full textMarine microbial ecosystems represent an important nexus in the Earth system, linking photosynthesis and biological productivity to global nutrient cycles and climate. Each year, marine biota export billions of tons of organic carbon into the deep ocean, maintaining an oceanic reserve that has a profound moderating effect on our climate (1). Our current understanding of these important microbial ecosystems has been shaped to a large extent by the terrestrial macroscopic world we see around us. In particular, the distinction between photosynthetic phytoplankton and heterotrophic zooplankton reflects a very familiar divide between plants and animals. While this distinction is intuitive, a great many species at the base of marine food webs defy such strict classifications (2). These flexible organisms, known as mixotrophs, not only use energy from the sun to take up nutrients and grow but they can also kill and eat other plankton. At present, we know that mixotrophy is the default lifestyle for many single-celled plankton, and we know that they often dominate marine communities (3). However, there remains considerable uncertainty as to how different environmental conditions select for mixotrophy across broad environmental gradients. While a number of hypotheses have been developed to explain the ecological niche of mixotrophs, we do not have a concrete understanding of how environmental factors shape the balance between different sources of nutrition in these communities. As such, it has been difficult to test the validity of hypotheses and to assess how the ecological role of mixotrophs might affect global ecosystem function, biogeochemical cycles, and climate. In PNAS, Edwards (4) presents a new synthesis of field observations and mathematical modeling that helps to address this knowledge gap
Environmental control of marine phytoplankton stoichiometry in the North Atlantic Ocean
No full textThe stoichiometric coupling of carbon to limiting nutrients in marine phytoplankton regulates the magnitude of biological carbon sequestration in the ocean. While clear links between plankton C:N ratios and environmental drivers have been identified, the nature and direction of these links, as well as their underlying physiological and ecological controls, remain uncertain. We show, with a well-constrained mechanistic model of plankton ecophysiology, that while nitrogen availability and temperature emerge as the main drivers of phytoplankton C:N stoichiometry in the North Atlantic, the biological mechanisms involved vary depending on the spatiotemporal scale and region considered. We find that phytoplankton C:N stoichiometry is overall controlled by nitrogen availability below 40° N, predominantly driven by ecoevolutionary shifts in the functional composition of the phytoplankton communities, while phytoplankton stoichiometric plasticity in response to dropping temperatures and increased grazing pressure dominates at higher latitudes. Our findings highlight the potential of “organisms-to-ecosystems” modeling approaches based on mechanistic models of plankton biology accounting for physiology, ecology, and trait evolution to explore and explain complex observational data and ultimately improve the predictions of global ocean models
Marine ecosystem model analysis using data assimilation
No full textNumerical modelling of the marine ecosystem requires the aggregation of diverse chemical and biological species into broad categories. To avoid large bias errors it is preferable to resolve as many explicit state variables and processes as possible. The cost of this increased complexity is greater uncertainty in model parameters and output. When comparing models, the importance of quantifying both bias error and the variability of unconstrained solutions was revealed as two marine ecosystem models were calibrated to data. Results demonstrated that all prior parameter information must include realistic error estimates if model uncertainty is to be quantified. Five simple ecosystem models were calibrated to observations from two North Atlantic sites; the Bermuda Atlantic Time-series Study (BATS) and the North Atlantic Bloom Experiment (NABE). Model-data mists were reduced by between 45 and 50%. The addition of model complexity (a parameterised microbial loop, a variable chlorophyll a to nitrogen ratio and dissolved organic nitrogen) led to larger improvements in model performance at BATS relative to NABE. Calibrated parameter values developed at NABE performed better than the default parameter values when applied at BATS. Solutions developed at BATS performed worse than the default values at NABE. The models lacked sufficient ecological complexity to function well at BATS. Errors in the model were masked by errors in the calibrated parameters and the models did not perform well with regard to independent data. The models were well suited to reproducing the NABE data, and the calibrated models performed relatively well at BATS. The models were sensitive to the underlying physical forcing. Although the ecosystem models were originally calibrated within a poor representation of the physical environment at BATS, results from experiments using an improved physical model support the conclusion that the ecosystem models lacked the required complexity at that site
Assessing an efficient “Instant Acclimation” approximation of dynamic phytoplankton stoichiometry
No full textThe variable elemental ratios of carbon to essential nutrients in marine organic matter affect the productivity of marine food-webs and the sequestration of carbon in the deep ocean. It is important that models of these systems are able to correctly reproduce observed trends. “Dynamic Quota” models have achieved some success in this regard, but the computational expense of transporting each state variable in ocean models has prevented many large-scale models from moving beyond a simpler “Fixed Stoichiometry” formulation. This article compares the Dynamic Quota and Fixed Stoichiometry models to a recent “Instant Acclimation” model, which combines the stoichiometric flexibility of the Dynamic Quota model with the computational efficiency of the Fixed Stoichiometry model. The Instant Acclimation model is mathematically equivalent to the Dynamic Quota model at equilibrium, and provides an accurate approximation under a wide range of dynamic conditions. The accuracy and computational efficiency of the Instant Acclimation model recommend it as a candidate for incorporating flexible stoichiometry into marine ecosystem models, especially in situations where the number of model state-variables is restricted
Cell morphological plasticity in response to substrate availability of a cosmopolitan polymorphic yeast from the open ocean
No full textPolymorphic yeasts can switch between unicellular division and multicellular filamentous growth. Although prevalent in aquatic ecosystems, such as the open ocean, we have a limited understanding of the controlling factors on their morphological variation in an aquatic ecology context. Here we show that substrate concentration regulates cell morphogenesis in a cosmopolitan polymorphic yeast, Aureobasidium pullulans, isolated from the pelagic open ocean and analyzed in liquid batch culture. Filamentous cell development was triggered only under high initial substrate conditions, suggesting that hyphal growth could be more advantageous under eutrophic conditions and may influence pelagic fungal interactions with particulate organic matter. Filamentous growth proportionally declined before the exhaustion of substrate and before budding yeast-type cell division entered stationary phase, possibly modulated by quorum sensing as previously evidenced in other polymorphic yeasts. We also found that budding yeast-type unicells decreased in size and became more elongated in shape in response to substrate depletion, resulting in higher cell surface area to volume ratios, which could affect yeast dispersal and/or provide a nutrient uptake advantage under oligotrophic conditions. Our results demonstrate resource-responsive morphological plasticity in a marine-derived polymorphic yeast, providing mechanistic insight into the ability of fungi to survive fluctuating environmental conditions such as in the open ocean.</p
Rapid evolution allows coexistence of highly divergent lineages within the same niche
Full text linkMarine microbial communities are extremely complex and diverse. The number of locally coexisting species often vastly exceeds the number of identifiable niches, and taxonomic composition often appears decoupled from local environmental conditions. This is contrary to the view that environmental conditions should select for a few locally well-adapted species. Here we use an individual-based eco-evolutionary model to show that virtually unlimited taxonomic diversity can be supported in highly evolving assemblages, even in the absence of niche separation. With a steady stream of heritable changes to phenotype, competitive exclusion may be weakened, allowing sustained coexistence of nearly neutral phenotypes with highly divergent lineages. This behaviour is robust even to abrupt environmental perturbations that might be expected to cause strong selection pressure and an associated loss of diversity. We, therefore, suggest that rapid evolution and individual-level variability are key drivers of species coexistence and maintenance of microbial biodiversity.</p
Selective constraints on global plankton dispersal
Full text linkMarine microbial communities are highly interconnected assemblages of organisms shaped by ecological drift, natural selection, and dispersal. The relative strength of these forces determines how ecosystems respond to environmental gradients, how much diversity is resident in a community or population at any given time, and how populations reorganize and evolve in response to environmental perturbations. In this study, we introduce a globally resolved population–genetic ocean model in order to examine the interplay of dispersal, selection, and adaptive evolution and their effects on community assembly and global biogeography. We find that environmental selection places strong constraints on global dispersal, even in the face of extremely high assumed rates of adaptation. Changing the relative strengths of dispersal, selection, and adaptation has pronounced effects on community assembly in the model and suggests that barriers to dispersal play a key role in the structuring of marine communities, enhancing global biodiversity and the importance of local historical contingencies.</p
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