Population extinction and metapopulation synchrony: a reassessment

Abstract

Synchronous dynamics of populations reduces metapopulation persistence. Thus, determining sources of synchrony is important for understanding metapopulations and biodiversity patterns in response to environmental disturbance. Previously, we found that the experimental extinction of two contiguous subpopulations of the butterfly Parnassius smintheus, increased synchrony among nearby subpopulations relative to distant controls. We hypothesized that increased synchrony was caused by either 1) a Moran‐like effect where the loss of immigrants simultaneously reduced the abundance of surrounding subpopulations or 2) an increase in dispersal among subpopulations surrounding the extinction. Reestablishment following extinction allowed for discrimination of these hypotheses. Additional data and new analyses using 24‐years of population growth in 12 nearby and control subpopulations before, during and after the experimental extinction show that our initial result was wrong. The ‘increase' in synchrony seen during the extinction was due to synchrony being low among treatment subpopulations during the pre‐extinction period, rather than an increase due to the experimental extinction. Lower synchrony among treatment subpopulations prior to extinction may have been due to less dispersal among treatment than among control subpopulations during the pre‐extinction period. Population crashes inducing synchrony (a Moran effect) during the extinction and post‐extinction periods also appear to have had greater and more lasting effects on synchrony for treatment than control subpopulations. Theoretical models show that local population extinction can increase synchrony in metapopulations, particularly for tightly regulated populations, but further experiments are needed to test this hypothesis.