Synchrony in local population dynamics of stream-dwelling Dolly Varden: do genetically similar groups show similar demography?

We investigated the relationship between genetic divergence and demographic dependence. Genetically related groups may consist of the same demographic unit or a single population,'' because high levels of dispersal may synchronize population dynamics. We examined this hypothesis by assessing the levels of synchrony in seven demographic parameters among locations supporting stream-dwelling Dolly Varden. We analyzed synchrony using demographic data collected over 10 years in five neighboring tributary streams (<7 km) where little genetic divergence was observed. The overall synchrony was moderate for age-0+ and >= age-1+ (average cross-correlation coefficient <(rho)over bar> = 0.32-0.56), but the synchrony decreased at later life stages (mature adults, (rho) over bar = 0.00-0.43). No significant temporal co-variation was observed for other demographic parameters (sex ratio and resident-to-migrant ratio, (rho) over bar = -0.19 and 0.38, respectively). Therefore, it appears that demographic synchrony was more prevalent for early life stages, but less so for later life stages, suggesting the demography of each tributary is unique. Furthermore, since an isolated location showed high levels of synchrony with the other locations, the main driver of synchrony is likely correlated environmental influences on demography (Moran effect) rather than dispersal. Pairwise synchrony was not correlated with geographical distance, but negatively correlated with the degree of genetic differentiation (F(ST)) in a few cases. Overall, however, we found little evidence that dispersal induces strong synchrony even among the neighboring tributaries where genetic analysis indicated considerable dispersal. Finally it is worth noting that the influences of dispersal may be different in terms of genetic and demographic contexts, and that density-dependent processes may mask patterns of observed synchrony.