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Section: Application Domains

Keywords : Bayesian estimation, Markov chain Monte Carlo (MCMC), Metropolis-Hastings, interacting Monte Carlo methods, particle methods.

Modeling and inference of ecological and environmental dynamics

Ecological and environmental dynamics are at the heart of some of today's leading issues (greenhouse effect, global warming, deforestation, loss of biodiversity, natural resources assessment etc.). For more than a decade, biologists and ecologists have been increasingly using computation modeling for a deeper understanding of the intricacies of these complex dynamics. This approach allows for improved assessments, accurate predictions and effective decision-making. Crucially, random effects need to be considered in this domain.

Most of the dynamical problems considered here are contrasted with the classical applications of hidden Markov models, such as automated speech recognition, target tracking or DNA sequence analysis. Indeed, the measurement data are highly noise-corrupted, acquired at very low frequencies, and on short time series (e.g. one measurement per year for several decades).

From the statistical point of view, the poor quality of data is an argument for using the Bayesian approach. The knowledge of ecological and environmental scientists allows for the choice of model used, as well as its structure. The Markovian framework offers a wide spectrum of possible models adapted to the Bayesian inference (see Section 3.2 ). Hence, in this context, we are drawn toward a model-driven approach.

Our first studies focused on the assessment of fishery resources. We adopted the Markovian formalism presented in Section 3.2 . The evolution of the total biomass and the relative abundance indexes are represented as a hidden Markov model. The hierarchical structure of this model allows for an efficient simulation-based inference of the a posteriori distribution law of the latent variables (state vector and parameter), given the observation data (catches and abundance indexes).

We recently considered the dynamics of tropical forests (see Section 6.2.4 ). Beyond “simple” economic production issues, recent developments in this area incorporate the concerns of biodiversity conservation and sustainable management. In this context, the need for spatial-temporal models becomes essential. Again, the Markovian framework offers many possibilities. In a statistical point of view, the main difficulty is to strike a compromise between the complexity of the model and the limitations of available data.


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