Charisma, an individual based macrophyte model

Plant plot movie
Researcher(s): E.H. (Egbert) van Nes
Other people involved: M. (Marten) Scheffer, H. (Hugo) Coops (RIZA), M.S. (Marcel) van den Berg (RIZA)
Conducted jointly with: RIZA
Funded by: RIZA
  1. The Charisma program (1200 KB)
  2. The manual (PDF)
  3. Thesis: van Nes, E.H. 2002. Controlling complexity in individual-based models of aquatic vegetation and fish communities. PhD Thesis. Wageningen University (download as pdf or order by email)

An individual-based simulation model for the dynamics of aquatic vegetation is developed and analysed. The model ('Charisma') can simulate the growth of one or more competing species of submerged macrophytes. It is spatially explicit and grid-based, but not focused on spatial processes. The model can also run as a more traditional age-structured population model.
Physiological data of macrophyte species and environmental variables (e.g., irradiation, temperature, extinction) are used as input of the model. The model produces spatial and temporal patterns of macrophytes, which can be compared with field data.

The model was used to analyse competition betweenChara aspera andPotamogeton pectinatus L. along a depth gradient. The parameter settings were based on literature, laboratory experiments and data from Lake Veluwemeer. The preliminary results show that in deeper waterChara is a better competitor. In shallow water coexistence is possible, but it is hard to replace an existingPotamogeton field byChara.

Furthermore, the occurrence of alternative stable states in shallow lakes is analysed using Charisma. Two alternative equilibria could be generated with the model, one without vegetation and one with vegetation. The parameters affecting the turbidity range where the system has alternative stable states and accompanying hysteresis, were analysed using the model.

Sensitivity analysis shows that a uncertainty in all parameters of 10 % leads to a range of model outputs in summer of about 40 %. In spring and autumn the sensitivity to parameter variation is much larger than during the rest of the year. The maximum biomass in summer is influenced most heavily by the maximum photosynthetic rate.

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