Evolutionary consequences of habitat loss for Pacific anadromous salmonids.

Michelle M Mcclure,Beth L Sanderson,Jeffrey C Jorgensen,Joseph Travis,Susan M Sogard,Timothy J Beechie,Richard W Carmichael,Stephanie M Carlson,Damon M Holzer,George R Pess,Mary E Power,Sonia E Sultan

doi:10.1111/j.1752-4571.2008.00030.x

Abstract

Large portions of anadromous salmonid habitat in the western United States has been lost because of dams and other blockages. This loss has the potential to affect salmonid evolution through natural selection if the loss is biased, affecting certain types of habitat differentially, and if phenotypic traits correlated with those habitat types are heritable. Habitat loss can also affect salmonid evolution indirectly, by reducing genetic variation and changing its distribution within and among populations. In this paper, we compare the characteristics of lost habitats with currently accessible habitats and review the heritability of traits which show correlations with habitat/environmental gradients. We find that although there is some regional variation, inaccessible habitats tend to be higher in elevation, wetter and both warmer in the summer and colder in the winter than habitats currently available to anadromous salmonids. We present several case studies that demonstrate either a change in phenotypic or life history expression or an apparent reduction in genetic variation associated with habitat blockages. These results suggest that loss of habitat will alter evolutionary trajectories in salmonid populations and Evolutionarily Significant Units. Changes in both selective regime and standing genetic diversity might affect the ability of these taxa to respond to subsequent environmental perturbations. Both natural and anthropogenic and should be considered seriously in developing management and conservation strategies.

Highlights

Loss of habitat and its attendant consequences have been implicated as the largest threat to endangered species in the United States (Wilcove et al 1998), and the loss of habitat is seen as the major cause of extinctions (Ehrlich and Ehrlich 1981; Wilson et al 2003)
Areas that are currently inaccessible are significantly higher in elevation, are colder in the winter, warmer in the summer, and drier than those that continue to be accessible to anadromous salmonids
Evolutionary consequences of anthropogenic impacts on salmonids are only beginning to be examined in the conservation literature

Summary

Introduction

Loss of habitat and its attendant consequences have been implicated as the largest threat to endangered species in the United States (Wilcove et al 1998), and the loss of habitat is seen as the major cause of extinctions (Ehrlich and Ehrlich 1981; Wilson et al 2003). Salmonid habitat loss and evolution habitat types might substantially alter the selective regime a species experiences. If a species shows local adaptation to habitats, habitat loss will reduce the variety of traits displayed by a species; if the loss of primary habitat displaces a species into less favorable or previously unutilized habitats with novel selective regimes, survival will require new phenotypes to emerge and spread (Miller and Sadro 2003). When there is considerable phenotypic plasticity underlying trait expression, individual response patterns (‘norms of reaction’) themselves can adaptively evolve as the benefit of responses for some habitats are lost (Scheiner 1993, 2002, and references therein)

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Conclusion