Effects of experimental population extinction for the spatial population dynamics of the butterfly Parnassius smintheus

While many studies have examined factors potentially impacting the rate of local population extinction, few experimental studies have examined the consequences of extinction for spatial population dynamics. Here we report results from a large-scale, long-term experiment examining the effects of local population extinction for the dynamics of surrounding populations. From 2001-2008 we removed all adult butterflies from two large, neighboring populations within a system of 17 subpopulations of the Rocky Mountain Apollo butterfly, Parnassius smintheus. Surrounding populations were monitored using individual, mark-recapture methods. We found that population removal decreased immigration to surrounding populations in proportion to their connectivity to the removed populations. Correspondingly, within-generation population abundance declined. Despite these effects, we saw little consistent impact between generations. The extinction rates of surrounding populations were unaffected and local population growth was not consistently reduced by the lack of immigration. The broader results show that immigration affects local abundance within generations, but dynamics are mediated by density-dependence within populations and by broader density-independent factors acting between generations. The loss of immigrants resulting from extinction has little impact on the persistence of local populations in this system.