Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 4386
Title: It's a bear market: evolutionary and ecological effects of predation on two wild sockeye salmon populations
Author: Jocelyn E. Lin, Jeffrey J. Hard, Kerry A. Naish, Daniel Peterson, R. Hilborn, L. Hauser
Publication Year: 2016
Journal: Heredity
Volume: 116
Pages: 447-457
DOI: 10.1038/hdy.2016.3
Keywords: wild sockeye

Predation can affect both phenotypic variation and population productivity in the wild, but quantifying evolutionary and demographic effects of predation in natural environments is challenging. The aim of this study was to directly estimate selection coefficients associated with bear predation in wild salmon populations spawning in pristine habitat. Using genetic pedigrees reconstructed from wild spawners, individual reproductive success was estimated in two populations of sockeye salmon (Oncorhynchus nerka) for two consecutive brood years with very different predation intensities. In combination with the pedigree, phenotypic data on individual adult body length, body depth, stream entry timing, and reproductive lifespan were used to calculate selection coefficients and genetic variance components using regression and animal models. Brown bears (Ursus arctos) consistently killed larger and more recently arrived adults, although selection differentials were small. In both populations, mean reproductive success was higher in the brood year experiencing lower predation intensity. In contrast, selection coefficients were similar across brood years, often indicating stabilizing selection on reproductive lifespan as well as directional selection for longer lifespan.  Despite these selection pressures, genetic covariation of morphology, phenology and lifespan appears to have maintained variation in spawner body size and stream entry timing in both populations. Our results therefore suggest considerable demographic but limited evolutionary effects of bear predation in the two study populations.

Official Citation:

Lin, J., J. J. Hard, K. Naish, D. Peterson, R. Hilborn, and L. Hauser. 2016. It's a bear market: evolutionary and ecological effects of predation on two wild sockeye salmon populations. Heredity 116:447-457 (doi:10.1038/hdy.2016.3; published online 10 February 2016).