  The spatial scale of population synchrony gives the characteristic distance
at which the population fluctuations are correlated. Therefore, it gives also
the characteristic size of the regions of simultaneous population depletion, or
even extinction. Single-species previous results imply that the spatial scale
of population synchrony is equal or greater (due to dispersion) than the
spatial scale of synchrony of environmental fluctuations. Theoretical results
on multispecies ecosystems points that interspecies interactions modify the
spatial scale of population synchrony. In particular, recent results on two
species ecosystems, for two competitors and for predator-prey, point that the
spatial scale of population synchrony generally increases as the fluctuations
propagates through the food web, i.e., the species more directly affected by
environmental fluctuations presents the smaller spatial scale of population
synchrony. Here, we found that this behaviour is generally true for a two
species ecosystem. The exception to this behaviour are the particular cases
where the population fluctuations of one of the species does not damp by its
own, but requires a strong transfer of the fluctuation to the other species to
be damped. These analytical results illustrate the importance of applying an
ecosystem rather than a single-species perspective when developing sustainable
harvestings or assessing the extinction risk of endangered species.
