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Application of mathematical modelling for examining plankton community patterns across a trophic gradient Jing--Yang Zhao, Maryam Ramin, Vincent Cheng, Jing G George B. A Arhonditsis h di i University of Toronto Objectives z Examination of the functional properties and the abiotic conditions di i under d which hi h the h different diff plankton l k groups can dominate or can be competitively excluded in oligooligo-, mesomeso- and eutrophic environments environments. z Elucidation of the aspects (i. (i.e., important causal links) of the complex interplay among physical, physical chemical and biological factors that drive epilimnetic plankton dynamics. dynamics. Simple Models versus Complex Models z Simple Models – Mathematically more sound – Results can be easily understood – Focus on one specific explanation of a phenomenon and n neglect eglect important aspects of system dynamics (spatial heterogeneity, individual variability) z Complex C l Models M d l – Mathematical features that can introduce artefacts – Results R lt can nott b be easily il understood d t d – Parameterization that more closely represents real world dynamics Food web structure Si N, P Diatoms z High g growth g rates z Strong P competitors z Weak N competitors z Si requirements z High sinking velocity z Lower Lo er temperature temperat re optima z High metabolic rate z High preference from zooplankton Cyanobacteria z Low L growth th rates t z Weak P competitors z Strong N competitors z Very low sinking velocity z High g temperature p optima p z Low metabolic rate z Low preference from zooplankton Green Algae Intermediate competitors To more realistically depict the continuum between diatomdiatom- and cyanobacteria--dominated communities in our numerical cyanobacteria experiments Cladocerans z z z z z z High grazing rates P-rich animals L Lower C C:N N ratio ti High temperature optima Higher metabolic rate Filter feeders Copepods z z z z z z Lower grazing rates N-rich animals L Lower C C:P P ratio ti Low temperature optima Lower metabolic rate Feeding selectivity Effects of ingested food quality and quantity on zooplankton ooplankton phosphor phosphoruss prod production ction efficienc efficiency Food Quality: HUFA, amino acids, protein content, digestibility Critical seston C:P threshold Phosphorus production efficiency Methodology Identification of the plausible parameter range (min, max) Assignment of a probability distribution: (i) form f (e.g., ( normal, l uniform) if ) (ii) calculation of the moments (central tendency, dispersion) Monte M t C Carlo l sampling li θi Literature information for θ 7,000 Monte Carlo sets θ k for each trophic state Parameter distributions θ f(xi,θ k) f( Model outputs ỹi Oli t hi Oligotrophic M Mesotrophic t hi Nutrient Loading Solar Radiation Epilimnion Temperature Hypolimnion Temperature Interannual variability Nutrient Loading Vertical Mixing Intraannual variability E Eutrophic t hi Oligotrophic environment Mesotrophic environment Eutrophic environment Diatoms Minimum intracellular phosphorus storage (Summer stratified period) Luxury uptake External Maximum phosphorus nutrients uptake k rate Maximum intracellular phosphorus storage (Eutrophic environments & winter period) Internal nutrients ti t Growth Phytoplankton y p cell Diatoms Diatoms Tight connection and positive relationship between diatoms (fastgrowing species with superior phosphorus competitors) and cladocerans (P-rich animals) that seems to reduce the grazing pressure exerted on the other residents of the phytoplankton community. Diatoms Diatoms and green algae directly compete against each other, as the th one group’s ’ ffunctional ti l properties ti (growth ( th rates, t storage t capacity, metabolic rates) and biomass levels can be significant predictors for the other one’s dynamics. Cyanobacteria Cladocerans Cladocerans • The PP-rich animals (e.g., Daphnia Daphnia)) contribute a significant proportion ti off the th excess carbon b and d nitrogen it b being i recycled l d iin the system. • The large large--bodied zooplankton grazers have the ability to reduce phytoplankton sensitivity to external perturbations. • The reproduction of the seasonal succession zooplankton patterns is VERY sensitive to the assigned temperature requirements for attaining optimal growth. Production of particulate matter with high C:P and N:P Ingestion Cladocerans Low N:P Excretion/egestion of material with ith strongly strongl increased C:P and N:P Copepods High N:P Excretion/egestion of material with ith moderately moderatel increased C:P and N:P Mineralization Nitrification Sedimentation (Hypothesis 1) Increased levels of depositing PON → possible effects on the diagenesis processes → alkalinity levels (Hypothesis 2) Increased levels of DON,, NO3 and NH4 Homeostatic regulation of zooplankton stoichiometries • Hypothesis yp 1: Processingg duringg digestion 1: g and assimilation pprocess (removing elements in closer proportion to their body ratio rather than to the element ratio in the food) • Hypothesis 2: 2: PostPost-assimilation processing and differential excretion of nutrients The proposed food quality/quantity parameterization ggives reasonable results!! References • Zhao, J., M. Ramin, V. Cheng, and G.B. Arhonditsis. Application of mathematical modeling for examining plankton community patterns across a trophic gradient: What is the role of the zooplankton functional groups? Ecological Research: Submitted Manuscript • Zhao, Zhao JJ., M M. Ramin Ramin, V V. Cheng Cheng, and G G.B. B Arhonditsis Arhonditsis. Competition patterns among phytoplankton functional groups: How useful are the complex biogeochemical models? Ecological Complexity: Submitted Manuscript
