Background/Question/Methods Spatial synchrony among conspecific populations is a critical component of metapopulation dynamics and is important to the long-term viability of populations. Meta-population dynamics are influenced by the landscape in which the populations occur. In a changing landscape how is spatial synchrony among conspecific populations effected, and are these effects felt equally across a community or are they species-specific? We have used over 30 years of presence-absence data to address these questions. A single individual has monitored four sites in California's Central Valley approximately every 10 days. We have used pair-wise correlations to estimate synchrony for 48 species. Additionally we have looked at how spatial synchrony has changed between the first and second halves of the study. We have also used presence-absence data to analyze species richness for each site over time. We have identified species that show regional decline, that are and are not synchronous, and that show the greatest changes in synchrony over time and have analyzed them based on life–history traits to find commonalities. We have used biannual data on regional land-use to consider these changes in population dynamics and community structure with respect to landscape changes from natural and agricultural to urban and the concomitant decrease in connectivity of habitats. Results/Conclusions All 4 sites show a significant decline in species richness over the time of study. Synchrony between populations has also declined regionally. This has occurred while there has been a marked increase in the conversion of land from agriculture and natural landscapes to urban and suburban uses. Species with a wide range of life-history traits show a decline in synchrony and occurrence, indicating that the changes within communities and between populations are not isolated to any particular, easily identified group. The changes observed in butterfly communities and land-use are not unique to butterflies or the northern Central Valley, although the ability to enumerate such trends with a long-term data set are. We have shown that both the richness of butterfly communities and their population dynamics are under threat as we modify their habitat.