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B Cazelles

Publications and source records attributed to B Cazelles.

6 recordsLinked to original sources
PubMed2001

Unexpected coherence and conservation.

The effects of migration in a network of patch populations, or metapopulation, are extremely important for predicting the possibility of extinctions both at a local and a global scale. Migration between patches synchronizes local populations and bestows upon them identical dynamics (coherent or synchronous oscillations), a feature that is understood to enhance the risk of global extinctions. This is one of the central theoretical arguments in the literature associated with conservation ecology. Here, rather than restricting ourselves to the study of coherent oscillations, we examine other types of synchronization phenomena that we consider to be equally important. Intermittent and out-of-phase synchronization are but two examples that force us to reinterpret some classical results of the metapopulation theory. In addition, we discuss how asynchronous processes (for example, random timing of dispersal) can paradoxically generate metapopulation synchronization, another non-intuitive result that cannot easily be explained by the standard theory.

Animal Migration↗
PubMed2001

Blowout bifurcation with non-normal parameters in population dynamics.

Interesting dynamic behaviors have been associated with the transverse stability of an invariant subspace (e.g., riddled basins or on-off intermittency). Recently, these complex behaviors have been generalized to cases of models with non-normal parameters showing that these behaviors might be widespread. In this Brief Report I demonstrate this type of complex dynamics in models of interacting populations for which the invariant subspace is defined by species extinction. In the context of the current biodiversity crisis, implications of these behaviors for population biology are discussed.

Journal Article↗
PubMed1997

Using the Kalman filter and dynamic models to assess the changing HIV/AIDS epidemic.

Many factors, including therapy and behavioral changes, have modified the course of the HIV/AIDS epidemic in recent years. To include these modifications in HIV/AIDS models, in the absence of appropriate external data sources, changes over time in the parameters can be incorporated by a recursive estimation technique such as the Kalman filter. The Kalman filter accounts for stochastic fluctuations in both the model and the data and provides a means to assess any parameter modifications included in new observations. The Kalman filter approach was applied to a simple differential model to describe the observed HIV/AIDS epidemic in the homo/bisexual male community in Paris (France). This approach gave quantitative information on the time-evolution of some parameters of major epidemiological significance (average transmission rate, mean incubation rate, and basic reproduction rate), which appears quite consistent with the recent epidemiological literature.

Disease Outbreaks↗
PubMed1994

Estimation of CHD risk in a French working population using a modified Framingham model. The PCV-METRA Group.

We adapt a recent model from the Framingham study (Circulation 1991; 83: 356-362) to predict CHD in France for both sexes over a large age range. Calculations were based on data from the French PCV-METRA study. In France, the Paris Prospective Study model could predict CHD but only for men aged 43-53 years. Applied to men 43-53 years from the PCV-METRA, the Framingham model estimated a 5-year CHD risk (4%) lower than the risk reported in the Framingham sample, but significantly higher than the risk estimated by the French model (2%). Differences in estimated CHD risk between the Framingham and the PCV-METRA samples were explained for only 30% by adjustment on major CHD risk factors (mainly HDL-cholesterol and tobacco). Modifying the intercept in the Framingham model, agreement with estimated risk by the French model was improved from 29 to 80%. By an appropriate change of the intercept, the Framingham model might be used to estimate CHD risk in other populations.

Adult↗