93 research outputs found

    Importance of allelopathy as peudo-mixotrophy for the dynamics and diversity of phytoplankton

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    Understanding the dynamics and diversity of marine phytoplankton is essential for predicting oceanic primary production, oxygen generation and carbon sequestration. Several top-down and bottom-up factors lead to complex phytoplankton dynamics. Complexities further arise from inter-species interactions within phytoplankton communities. Consequently, some of the basic questions on phytoplankton diversity, identified long ago, still puzzle the ecologists: for example, what regulates the diversity in simple systems where species compete for limiting resources? In this context, allelopathic interaction among phytoplankton species has been identified as a potential driver of their dynamics and regulator of their diversity. This chapter deals with the importance of allelopathy in regulating the outcome of nutrient competition among phytoplankton species, through analysis of a resource-competition model. It demonstrates that, through the mechanism of pseudo-mixotrophy - proposed earlier by the author - allelopathy provides essential growth advantage to weaker competitors, and stabilizes resource competition, which ensures the coexistence of two phytoplankton on a single nutrient. In simple nutrient-phytoplankton interactions where higher-trophic influences are negligible, this mechanism theoretically promotes phytoplankton diversity, and can potentially support high diversity in natural phytoplankton communities

    Toxin-allelopathy among phytoplankton species prevents competitive exclusion

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    Toxic or allelopathic compounds liberated by toxin-producing phytoplankton (TPP) acts as a strong mediator in plankton dynamics. On an analysis of a set of phytoplankton biomass-data that have been collected by our group in the North-West part of the Bay of Bengal, and by analysis of a three-component mathematical model under a constant as well as a stochastic environment, we explore the role of toxin-allelopathy in determining the dynamic behaviour of the competing-phytoplankton species. The overall results, based on analytical and numerical wings, demonstrate that toxin-allelopathy due to the toxin-producing phytoplankton (TPP) promotes a stable coexistence of those competitive phytoplankton that would otherwise exhibit competitive exclusion of the weak species. Our study suggests that TPP might be a potential candidate for maintaining the coexistence and diversity of competing phytoplankton species.Comment: 29 pages, 6 figures, Journal Pape

    Oscillations in continuous culture populations of Streptococcus pneumoniae: population dynamics and the evolution of clonal suicide

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    Agents that kill or induce suicide in the organisms that produce them or other individuals of the same genotype are intriguing puzzles for ecologists and evolutionary biologists. When those organisms are pathogenic bacteria, these suicidal toxins have the added appeal as candidates for the development of narrow spectrum antibiotics to kill the pathogens that produce them. We show that when clinical as well as laboratory strains of Streptococcus pneumoniae are maintained in continuous culture (chemostats), their densities oscillate by as much as five orders of magnitude with an apparently constant period. This dynamic, which is unanticipated for single clones of bacteria in chemostats, can be attributed to population-wide die-offs and recoveries. Using a combination of mathematical models and experiments with S. pneumoniae, we present evidence that these die-offs can be attributed to the autocatalytic production of a toxin that lyses or induces autolysis in members of the clone that produces it. This toxin, which our evidence indicates is a protein, appears to be novel; S. pneumoniae genetic constructs knocked out for lytA and other genes coding for known candidates for this agent oscillate in chemostat culture. Since this toxin lyses different strains of S. pneumoniae as well as other closely related species of Streptococcus, we propose that its ecological role is as an allelopathic agent. Using a mathematical model, we explore the conditions under which toxins that kill members of the same clone that produces them can prevent established populations from invasion by different strains of the same or other species. We postulate that the production of the toxin observed here as well as other bacteria-produced toxins that kill members of the same genotype, ‘clonal suicide’, evolved and are maintained to prevent colonization of established populations by different strains of the same and closely related species

    Texas A&M University – Lake Granbury and Bosque River Assessment Final Scientific/Technical Report

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    The “Texas A&M University – Lakes Granbury and Waco, and Bosque River Assessment” project was developed to address two separate water quality issues in Central Texas. Prior work in each waterbody has identified major water quality concerns and laid the ground work for the activities conducted in this project. Lake Granbury and the Bosque River both serve vital roles in the Brazos River watershed. Lake Granbury is a reservoir constructed on the main stem of the Brazos River in Hood County, Texas and provides a potable water supply for over 250,000 area residents, cooling water for a natural gas fired and a nuclear power plant, vital flood control for the city of Waco and a critical economic stimulus for the city of Granbury and surrounding areas. The Bosque River, also in the Brazos River watershed plays a vital role in Central Texas as well; it feeds Lake Waco and supplies water for 200,000 Central Texans. Lake Granbury has experienced recent toxic blooms of Prymnesium parvum (Golden algae) that have resulted in massive fish kills and concerns about general water quality. Lake Waco, a reservoir constructed on the main stem of the Bosque River, has viable P. parvum populations, but does not experience harmful blooms. Thus, comparisons between Lakes Granbury and Waco allow for comparisons of environmental conditions leading to bloom formation. Both Lake Granbury and Lake Waco are critical to this region as being primary water supplies, sources of revenue and recreational hotspots. This project addressed these water quality issues by providing critical information about the relationships between the contaminants (Golden algae and nutrients) and environmental factors in the respective watersheds. In Lakes Granbury and Waco, various plankton, nutrient and water quality samples were collected at fixed-location stations, and high-resolution spatial maps were generated using an on-board dataflow technology of various plankton and water quality parameters. Linkages between the toxic Golden algae blooms and environmental conditions were examined. In addition, a numerical model of Lake Granbury was developed and continues to be refined. Bloom forming processes were investigated with this model. In the Bosque River, elevated nutrient levels have lead to increased aquatic vegetation growth and subsequent taste and odor problems in Lake Waco. This project enlists physically based computer modeling to determine the nutrient and sediment removal capabilities of implementing recommended Best Management Practices (BMPs) throughout the watershed. Results of this project indicate areas where specific management strategies will provide the most pollutant control for the cost to implement the practice. Each project is focused on addressing specific water quality issues in a specific water body, but each will provide valuable information that can be used to correct water quality concerns in other watersheds with similar problems. Ultimately, the project will result in improved water quality for consumptive, recreational, and industrial uses and will help to sustain the economic stimulus resulting from these water bodies

    Resisting annihilation: relationships between functional trait dissimilarity, assemblage competitive power and allelopathy

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    Abstract Allelopathic species can alter biodiversity. Using simulated assemblages that are characterised by neutrality, lumpy coexistence and intransitivity, we explore relationships between within-assemblage competitive dissimilarities and resistance to allelopathic species. An emergent behaviour from our models is that assemblages are more resistant to allelopathy when members strongly compete exploitatively (high competitive power). We found that neutral assemblages were the most vulnerable to allelopathic species, followed by lumpy and then by intransitive assemblages. We find support for our modeling in real-world time-series data from eight lakes of varied morphometry and trophic state. Our analysis of this data shows that a lake's history of allelopathic phytoplankton species biovolume density and dominance is related to the number of species clusters occurring in the plankton assemblages of those lakes, an emergent trend similar to that of our modeling. We suggest that an assemblage's competitive power determines its allelopathy resistance

    Productivity analysis and non-linear gain scheduling approach for multi-species bioprocesses with product inhibition

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    International audienceBioprocesses with product inhibition are known to allow species coexistence. In this work, we first study the productivity of the different possible equilibria, depending on the operating conditions, and show that single species offers the best performances. Then, we propose a control strategy to stabilize the dynamics about the desired equilibria, in presence of instability. Based on output feedback linearization, we propose a family of controllers and a gain-scheduling approach to adapt the controller. Finally, we illustrate our approach on numerical simulations, showing that the attraction basin of the closed-loop system is improved by considering the gain-scheduling approach
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