Movement and gene flow in an actively sedentary stream fish, the mottled sculpin (Cottus bairdi).

摘要

The cues to and extent of individual movements constitute vital determinants of population dynamics, but the difficulty of observing long moves in the field has limited our understanding of the ecology of mobile species. This study assessed whether small-scale moves could be "scaled up" to predict longer moves. It also experimentally tested whether the scale-dependent spatial patterns evident in the observational data could be explained by conspecific copying. I used observational, experimental, and genetic approaches to assess movement in the mottled sculpin, Cottus bairdi, a stream fish with notably restricted dispersal, over multiple spatial and temporal scales.; Observational and experimental data on reach-scale (20 to 160m) movements demonstrated that C. bairdi use conspecific density as a direct cue to reach-scale movement, even though C. bairdi use prey density as the proximal cue to fine-scale (less than 2m) moves. Mark-recapture surveys showed that C. bairdi moved substantial distances (greater than 20m) more often than previous work indicated and that the correlates of movement changed seasonally. Mark-recapture also indicated, and field manipulations of C. bairdi density confirmed, that C. bairdi used conspecific density as a proximal cue for movement. The aggregation probably resulted from C. bairdi using conspecifics as an indicator of good foraging habitat, a process known as conspecific copying. Microsatellite DNA samples from C. bairdi over 5.3 km of stream length showed strong isolation-by-distance, with significant differences between locations less than 1 km apart, which supports stepping-stone dispersal in this population. Even so, the gene flow inferred from the genetic data still exceeded the dispersal estimates derived from the mark-recapture data. The genetic data also contrasted with the mark-recapture data in the cues to and direction of dispersal, but these differences were more likely due to differences in methods and sampling areas rather than an actual conflict in their results. Thus, these data show that even an exceptionally sedentary species may exhibit significant and distinct movement patterns from the patch to the population scale.