Some aspects of the relationship between conservativeness of a dynamical system (namely the preservation of a finite measure) and the existence of a Poisson structure for that system are analyzed. From the local point of view, due to the Flow-Box Theorem we restrict ourselves to neighborhoods of singularities. In this sense, we characterize Poisson structures around the typical zero-Hopf singularity in dimension 3 under the assumption of having a local analytic first integral with non-vanishing first jet by connecting with the classical Poincaré center problem. From the global point of view, we connect the property of being strictly conservative (the invariant measure must be positive) with the existence of a Poisson structure depending on the phase space dimension. Finally, weak conservativeness in dimension two is introduced by the extension of inverse Jacobi multipliers as weak solutions of its defining partial differential equation and some of its applications are developed. Examples including Lotka-Volterra systems, quadratic isochronous centers, and non-smooth oscillators are provided. 973702702.From the point of view of the relationship with Poisson systems and their diffeomorphic transformation properties, it will be useful for us to know how inverse integrating factors change under orbital equivalence of vector fields, see [3,8] for further details.Proposition 3. Let Φ be a diffeomorphism in Ω ⊂ R n with non-vanishing Jacobian determinant J Φ on Ω and let η : Ω → R be such that η ∈ C 1 (Ω) and η(x) = 0 everywhere in Ω. If V is an inverse Jacobi multiplier of the C 1 -vector field Y in Ω then η(V • Φ)/J Φ is an inverse Jacobi multiplier of the orbitally equivalent vector field η Φ * (Y).