Landscape characteristics drive the schedule of salmon subsidies and species they support in terrestrial ecosystems

Background/Question/Methods

The transport of materials by migratory animals among habitats can have considerable ecological effects, but little is understood in how the timing of resource subsidies affects recipient communities.  Intraspecific diversity in the spawn-timing of Pacific salmon (Oncorhynchus sp.) may have substantial implications for terrestrial organisms that depend on salmon resources, yet we lack a general understanding of processes that generate spawn-timing variability in the wild. Environmental variation among spawning sites may explain some of the diversity in the timing and spatial pattern of a salmon spawning.  We hypothesized that landscape attributes influence salmon phenology that therefore shape the schedule of scavenging opportunities for animals that depend on salmon. Multivariate approaches were used to evaluate environmental characteristics that contributed to variation in salmon spawning among 39 streams in the Wood River basin of southwest Alaska.  We also assessed whether the variation in spawn timing was associated with the phenology of scavenging activity of coastal brown-bears (Ursus arctos), Glaucus–winged gulls (Larus glaucescens), and the bloom timing of riparian plants (Angelica genuflexa) throughout the river network.

Results/Conclusions

Principal component analysis (PCA) indicated that topography, hydrology, and temperature influences salmon spawn timing life histories.  Variation in summer temperature has the strongest effect on the variation in salmon spawn timing, where cold streams supported earlier spawning salmon populations whereas warmer streams had salmon populations that spawn weeks to months later. The diversity in salmon residence among spawning sites extended the length of season that salmon were available for brown bears and Glaucus –winged gulls from 3 weeks to more than 2 months. Salmon spawn-timing was also indirectly linked to bloom timing of riparian plants through riparian pollinators that were composed of 85-99% salmon-derived material. We found that salmon spawning date explained a substantial amount (71%) of the observed seasonal variation in peak flowering date among streams compared with other environmental characteristics in the riparian area. Thus, our research highlights how geomorphology and hydrology act as important drivers of water temperature which influences the intraspecific variation in salmon and the species they support at the landscape level.