Fine-scale differences in genetic and census population size ratios between two stream fishes
Comparing the ratio of effective number of breeders (N b ) to adult population size (N) among closely related coexisting species can provide insights into the role of life history on N b /N ratios and inform conservation programs towards limiting the loss of evolutionary potential in natural populations. We estimated N b and N in two coexisting salmonid fishes (Brook trout and Atlantic salmon) for 3–4 consecutive years in two small, adjacent streams in Newfoundland, Canada, using mark-recapture (N), linkage disequilibrium (N b(LD)), and sibship frequency approaches (N b(Sib) ). We found that N b /N ratios were about 20-fold greater in Atlantic salmon than in brook trout (mean 0.20, range 0.06–0.56 vs. mean 0.02, range 0.01–0.05, respectively). This difference was consistent across N b estimators. In addition, we found that removing migrants reduced N b : the strength of the effect was weak for N b(LD) and much stronger for N b(Sib). Our results highlight the importance of subtle ecological differences and gene flow in shaping N b /N. They also provide some evidence that the linkage between demographic and evolutionary processes varies between closely related taxa and suggest that a more complete understanding of the N b /N range across various species is an important component of conservation genetics and management.
KeywordsCensus population size Effective number of breeders Genetic monitoring Mark-recapture Salmonid
We thank S. Smart, P. Debes, J-M. Matte, K. Marin and M. Heath for fieldwork, as well as Dr. John Carlos Garza and two anonymous reviewers for their helpful comments on previous versions of this manuscript. This research was funded by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant and Accelerator Award to D.J. Fraser, a Vladimir J. Elgart Graduate Entrance Scholarship and two Quebec Center for Biodiversity Science (QCBS) awards to T.A. Bernos, and an NSERC PGS Scholarship to M. Yates.
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