Mathematical modeling of colony formation in algal blooms: phenotypic plasticity in cyanobacteria
In this paper, we analyzed a mathematical model of algal-grazer dynamics, including the effect of colony formation, which is an example of phenotypic plasticity. The model consists of three variables, which correspond to the biomasses of unicellular algae, colonial algae, and herbivorous zooplankton. Among these organisms, colonial algae are the main components of algal blooms. This aquatic system has two stable attractors, which can be identified as a zooplankton-dominated (ZD) state and an algal-dominated (AD) state, respectively. Assuming that the handling time of zooplankton on colonial algae increases with the colonial algae biomass, we discovered that bistability can occur within the model system. The applicability of alternative stable states in algae-grazer dynamics as a framework for explaining the algal blooms in real lake ecosystems, thus, seems to depend on whether the assumption mentioned above is met in natural circumstances.
KeywordsBistability Colony size Defensive morphology Handling time Selective feeding
We are grateful to K. Shibata for permission to use a microscopic photo of Microcystis and the useful discussions. This study is supported by the Global COE Program “Global Eco-Risk Management from Asian View Points” from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
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