Earlier Migration Timing, Decreasing Phenotypic Variation, and Biocomplexity in Multiple Salmonid Species

Ryan P. Kovach,Jesse D. Echave,John E. Joyce,David A. Tallmon,Mark S. Lindberg,Stephanie M. Carlson

doi:10.1371/journal.pone.0053807

Abstract

Climate-induced phenological shifts can influence population, evolutionary, and ecological dynamics, but our understanding of these phenomena is hampered by a lack of long-term demographic data. We use a multi-decade census of 5 salmonid species representing 14 life histories in a warming Alaskan stream to address the following key questions about climate change and phenology: How consistent are temporal patterns and drivers of phenology for similar species and alternative life histories? Are shifts in phenology associated with changes in phenotypic variation? How do phenological changes influence the availability of resource subsidies? For most salmonid species, life stages, and life histories, freshwater temperature influences migration timing – migration events are occurring earlier in time (mean = 1.7 days earlier per decade over the 3–5 decades), and the number of days over which migration events occur is decreasing (mean = 1.5 days per decade). Temporal trends in migration timing were not correlated with changes in intra-annual phenotypic variation, suggesting that these components of the phenotypic distribution have responded to environmental change independently. Despite commonalities across species and life histories, there was important biocomplexity in the form of disparate shifts in migration timing and variation in the environmental factors influencing migration timing for alternative life history strategies in the same population. Overall, adult populations have been stable during these phenotypic and environmental changes (λ ≈1.0), but the temporal availability of salmon as a resource in freshwater has decreased by nearly 30 days since 1971 due to changes in the median date of migration timing and decreases in intra-annual variation in migration timing. These novel observations advance our understanding of phenological change in response to climate warming, and indicate that climate change has influenced the ecology of salmon populations, which will have important consequences for the numerous species that depend on this resource.

Highlights

Along the coasts of the northern Pacific Ocean, salmonids (Oncorhynchus and Salvelinus spp.) are a vital link between marine and terrestrial ecosystems, and provide a massive source of nutrients to coastal food webs [1,2]
Considerable life history variation exists within and among these salmonid species (See Text S1, [9]), and data for different life stages provide a unique opportunity to understand whether responses are consistent across life history strategies within a species. Using these data we address a number of questions: (1) has inter-annual migration timing changed in those salmonid species and life histories occupying Auke Creek, Alaska, USA; (2) what environmental or life history factors appear to play a role in determining migration timing; (3) are there temporal trends in VP in migration timing, and, if so, (4) are these trends correlated with changes in the average phenotype; (5) how variable are phenological responses and the environmental factors influencing phenology across different species, life-stages, and life-histories; and (6) have changes in the central tendency and variance in migration timing altered the availability of salmon as an ecosystem service?
Our results show that the migration timings of Auke Creek salmonids have changed across species and life history types over the last 30–47 years

Summary

Introduction

Along the coasts of the northern Pacific Ocean, salmonids (Oncorhynchus and Salvelinus spp.) are a vital link between marine and terrestrial ecosystems, and provide a massive source of nutrients to coastal food webs [1,2]. An important aspect of salmonid biology that may need to respond to climate change is migration timing because this trait is closely adapted to local environmental conditions, temperature [4], and influences individual fitness by affecting survival and reproductive success [5,6,7,8]. Due to their important ecological role [1,2] and predictable migratory timing [9], many species are thought to have adapted their phenologies to correspond with the presence of adult salmon in freshwater [10,11].

Methods

Results

Conclusion