Spatial Synchrony in Wisconsin Karner Blue (Lepidoptera: Lycaenidae) Populations

We analyzed geographic patterns of Karner blue (Lycaeides melissa samuelis Nabokov, Lepidoptera: Lycaenidae) population fluctuations in summer broods in central and northwestern Wisconsin and spring+summer broods in central Wisconsin. We removed possible effects of population trends by analyzing residuals from a regression of each site’s population index vs. year. We then calculated correlation coefficients (r) of these residuals for all site-pairs separately for 1992- 2005 (26 sites, N = 325 site-pairs), 1995-2005 (21 sites, N = 210), and 1998-2005 (14 sites, N = 91). We analyzed patterns in these r values relative to distance between sites using correlations vs. distance and using pairwise comparisons of different distance categories (0-3 km up to 223-264 km apart). Karner blues showed significant (P \u3c 0.05) population synchrony over all distances. Spatial autocorrelation was strongest among sites \u3c3 km apart, then gradually leveled off at greater distances. Statistical power increased when we added three years but the number of sites did not decrease greatly (1995-2005 vs. 1998-2005 analyses) and when using an annual index combining spring+summer indices instead of just summer. The spatial autocorrelation extending over the entire study region suggests that environmental factors like weather provide some synchronization of Karner blue populations. Their much higher local synchrony is consistent with the species’ short dispersal distance. Their local and regional spatial autocorrelation increases the likelihood of correlated local extinctions during low fluctuation broods, especially when these coincide with unfavorable weather or adverse habitat events