Quantifying spatial correlations in extinction risk for an aphid metapopulation

Metapopulation persistence depends on dispersal offsetting local extinction risks. The mitigating power of dispersal to offset local extinction risks is substantially reduced if extinction risks are highly spatially correlated. Extinction risks are likely to be spatially correlated when mechanisms driving local extinction act on large spatial scales, such as climatic events or far-ranging predators. In this paper I develop a method to quantify spatial correlations in local extinction risks within a region. I then show that colonies of the aphid Aphis lugentis within clusters of their host plant, Senecio bigelovii, do not have strong spatial correlations in extinction risks, even though the primary mechanism for colony extinction is over-predation by far-ranging predators (ladybugs and syrphid flies). Consequently, dispersal potentially plays an important role offsetting local extinction. Aphids did experience a weak, but significantly positive correlation in extinction risk in one of the two years of this study as well as increasing extinction risks across all plant clusters in both years. These observations point to important gaps in our understanding of how population synchrony affects metapopulation persistence.