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 Cage-1? (average cross-correlation coefficient q ¼ 0:32À0:56), but the synchrony decreased at later life stages (mature adults, q ¼ 0:00À0:43). No significant temporal co-variation was observed for other demographic parameters (sex ratio and resident-to-migrant ratio, q ¼ À0:19 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.

Nomoto K, Omiya H, Sugimoto T, Akiba K, Edo K, Higashi S. Potential negative impacts of introduced rainbow trout on endangered Sakhalin taimen through redd disturbance in an agricultural stream, eastern Hokkaido.
Ecology of Freshwater Fish 2010: 19: 116–126. © 2009 John Wiley & Sons A/S Abstract –  Sakhalin taimen (Hucho perryi) populations have decreased in Hokkaido, northernmost Japan, primarily because of overexploitation and habitat degradation. Here we document another threat to this species, that of spawning redd superimposition by artificially introduced rainbow trout (Oncorhynchus mykiss). Sakhalin taimen and rainbow trout are the only spring‐spawning salmonid species in Hokkaido. In 2006–2008, spawning activities of both these species were observed in a Hokkaido stream, and it was determined that their spawning periods overlapped during mid‐late April. They also spawned at similar water velocities, depths and substrate compositions. Although female Sakhalin taimen were larger than female rainbow trout, their egg burial depths were nearly identical. During the observation period, rainbow trout redds were approximately five times more abundant than Sakhalin taimen redds, and about 30% of the observed Sakhalin taimen redds were superimposed by rainbow trout redds. The high degree of spatial and temporal overlap in spawning, the similar egg burial depths of both species, and the high proportion of superimposed redds suggest that the introduced rainbow trout impact the endangered Sakhalin taimen in Hokkaido, and possibly, in other areas where the two species occur together.

Egg hatching rates of F1 hybrids among three fishes, Japanese dace Tribolodon hakonensis, Pacific redfin T. brandtii, and rosyface dace T. sachalinensis were compared with pure crosses. They are deeply diverged (10-20 million years ago) but naturally hybridizing. Although crosses involving female rosyface dace were not available, hatching success was high among all combinations of hybrids (76 ± 23 %) and comparable to pure crosses (86 ± 8 %), implying ecological or genetic isolation mechanisms maintaining each species in later life stages.

Understanding environmental factor determining ecological niche is very important to elucidating the distribution of species, and also revealing how closely related species are able to coexist in a particular region. Here, we applied ecological niche modeling to develop the ecological niches of two hynobiid salamanders: Salamandrella keyserlingii and Hynobius retardatus which are co‐occurring on Hokkaido Island, Japan. We, then, tested hypotheses about ecological niche differentiation between the two species. Our models showed that the potential distribution of S. keyserlingii was strictly limited to a small area at Kushiro Marsh, while the suitable distribution of H. retardatus was covered widely on Hokkaido Island. The results revealed the little geographic range overlap and the differentiation on the requirements of the ecological condition between the two species. We found nonequivalent niches in identity tests and counterintuitive results in background tests, indicating that S. keyserlingii has used a habitat subset of H. retardatus. Overall, our result contributed to understand the ecological niche space, and suggest the historical formation of these species on Hokkaido Island. The models can also be used to aid conservation purposes, such as habitat management, planning and designation of protected areas.

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