  The kaon to pion ratio $K^+/\pi^+$ and the scaled variance $\omega^-$ for
fluctuations of negatively charged particles are studied within the statistical
hadron resonance gas (HRG) model and the Ultra relativistic Quantum Molecular
Dynamics (UrQMD) transport model. The calculations are done for p+p, Be+Be,
Ar+Sc, and Pb+Pb collisions at the CERN Super Proton Synchrotron energy range
to reveal the system size dependence of hadron production. For the HRG
calculations the canonical ensemble is imposed for all conserved charges. In
the UrQMD simulations the centrality selection in nucleus-nucleus collisions is
done by calculating the forward energy $E_{\rm F}$ deposited in the Projectile
Spectator Detector, and the acceptance maps of the NA61/SHINE detectors are
used. A comparison of the HRG and UrQMD results with the data of the NA61/SHINE
Collaboration is done. To understand a difference of the event-by-event
fluctuations in p+p and heavy ion collisions the centrality selection procedure
in the sample of all inelastic p+p events is proposed and analyzed within the
UrQMD simulations.

Nuclear Theory;High Energy Physics - Experiment;High Energy Physics - Phenomenology;Nuclear Experiment