  A large number of theoretical studies predict that the dynamics of spatially
structured populations (metapopulations) can be altered by constant
perturbations to local population size. However, these studies presume large
metapopulations inhabiting noise-free, zero-extinction environments, and their
predictions have never been empirically verified.
  Here we report an empirical study on the effects of localized perturbations
on global dynamics and stability, using fruitfly metapopulations in the
laboratory. We find that constant addition of individuals to a particular
subpopulation in every generation stabilizes that subpopulation locally, but
does not have any detectable effect on the dynamics and stability of the
metapopulation. Simulations of our experimental system using a simple but
widely applicable model of population dynamics were able to recover the
empirical findings, indicating the generality of our results. We then simulated
the possible consequences of perturbing more subpopulations, increasing the
strength of perturbations, and varying the rate of migration, but found that
none of these conditions were expected to alter the outcomes of our
experiments. Finally, we show that our main results are robust to the presence
of local extinctions in the metapopulation.
  Our study shows that localized perturbations are unlikely to affect the
dynamics of real metapopulations, a finding that has cautionary implications
for ecologists and conservation biologists faced with the problem of
stabilizing unstable metapopulations in nature.
