No limiar tênue entre teoria e realidade, sazonalidade e caos em sistemas planctônicos
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2009-02-26
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Universidade Federal de Goiás
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The Chaos Theory is an alternative tool to stochastic dynamic modeling when
target biological systems show irregular and no predictive behavior. The plankton is a
model group of organisms to theoretical and experimental investigations in chaotic
dynamics due to its intrinsic biological characteristics as small size, high reproductive
rate and short life cycle, with the additional advantage of its public interest related to
practical problems. In this work we investigated the dynamical aspects of a
NutrientPhytoplankton-Zooplankton seasonal forced model, created by means of the
addition of the Zooplankton level on a Nutrient-Phytoplankton seasonal forced model
that show chaotic behavior, proposed by Huppert et al. (2005). An important outcome
of the Huppert’s model is that the intensity of the seasonal forcing is the control
parameter of the system. We investigated the zooplankton effect on the stability of the
model, and the chaos control by means of pulses in the intensity of the seasonal forcing.
Our results show that strong and weak seasonal forcing implicates in cyclical
fluctuations of phytoplankton populations, and those cycles had higher amplitude in
strong seasonal forcing. Between those two extremes, there is chaos. The zooplankton
mortality is a fundamental component of the behavior of the model. In fact, despite of
seasonal forcing values that can promote chaotic behavior, the model can show cyclic
behavior to some values of mortality rates. This suggests that absence of top-down
control in the models built to understand phytoplanktonic dynamics (blooms are only a
consequence of this), result in an over-simplification and lack of conceptual
comprehension of the system. Our results show that periodic pulses can be able to
control the chaos on moderate seasonal forcing, and to promote chaos to weak and
strong seasonal effects. The pulses are theoretical indicatives of how climatic changes
influences a seasonal variable can to affect the dynamics aspects of planktonic systems.
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FERREIRA, Heury Sousa. No limiar tênue entre teoria e realidade, sazonalidade e caos em sistemas planctônicos. 2009. 52 f. Dissertação (Mestrado em Ecologia e Evolução) - Instituto de Ciências Biológicas, Universidade Federal de Goiás, Goiânia, 2009.