Concentration phenomenon in some non-local equation
Olivier Bonnefon Jérôme Coville Guillaume Legendre
We are interested in the long time behaviour of the positive solutions of the Cauchy problem involving the integro-differential equation
$\partial_t u(t,x)\\=\int_{\Omega }m(x,y)\left(u(t,y)-u(t,x)\right)\,dy+\left(a(x)-\int_{\Omega }k(x,y)u(t,y)\,dy\right)u(t,x),$
supplemented by the initial condition
$\Omega $
, where the domain
$\Omega $
is a, the functions
are non-negative kernels satisfying integrability conditions and the function
is continuous. Such a problem is used in population dynamics models to capture the evolution of a clonal population structured with respect to a phenotypic trait. In this context, the function
represents the density of individuals characterized by the trait, the domain of trait values
$\Omega $
is a bounded subset of
, the kernels
respectively account for the competition between individuals and the mutations occurring in every generation, and the function
represents a growth rate. When the competition is independent of the trait, that is, the kernel
is independent of
, (
), we construct a positive stationary solution which belongs to
inthe space of Radon measures on
$\Omega $
$\mathbb{M}(\Omega )$
.Moreover, in the case where this measure
is regular and bounded, we prove its uniqueness and show that, for any non-negative initial datum in
$L^1(\Omega )\cap L^{\infty}(\Omega )$
, the solution of the Cauchy problem converges to this limit measure in
$L^2(\Omega )$
. We also exhibit an example for which the measure is singular and non-unique, and investigate numerically the long time behaviour of the solution in such a situation. The numerical simulations seem to reveal a dependence of the limit measure with respect to the initial datum.
keywords: Non-local equation demo-genetics concentration phenomenon asymptotic behaviour

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