Climate-Induced Trends In Predator–Prey Synchrony Differ Across Life-History Stages Of An Anadromous Salmonid

Testing the Impacts of Climate Change on Salmon

Changes to the Timing of Seasonal Events

A major concern stemming from climate change is that differential shifts in phenology — the timing of seasonal biological events such as migration — will decouple consumers (e.g., predators) from their food resources (e.g., prey; Visser and Both 2005; Thackeray et al. 2010). Predator phenologies must match interannual variation in prey availability (Hjort 1914; Cushing 1969, 1990), which is often achieved using phenological cues (e.g., temperature) that are indirectly associated with optimal foraging conditions. However, phenological cues can become unreliable under changing climatic conditions (Visser and Holleman 2001), limiting the ability of predators to track shifting prey phenologies and creating trophic mismatches (Visser and Both 2005).

Changes in Predator-Prey Interactions

Trophic mismatches can decrease predator abundance (Both et al. 2006) and potentially impact the larger ecosystem by altering predator–prey interactions across multiple trophic levels (Winder and Schindler 2004). Most studies have focused on potential trophic mismatches during a single life-history event. However, predators often benefit from matching prey during multiple life-history stages, such as entry into the ocean (downstream migration) and return to fresh water (upstream migration) for anadromous fish.

Summary of Study

The Influence of Life Stages

Differential climate-induced shifts in phenology can create mismatches between predators and prey, but few studies have examined predator–prey mismatch across multiple life-history stages. We used long-term data from a warming stream with shifting salmonid migration timings to quantify intra-annual migration synchrony between predatory Dolly Varden (Salvelinus malma) and Pacific salmon prey and examined how predator–prey synchrony has been influenced by climate change.

Overall, we show that climate change can have differing impacts on predator–prey synchrony across life-history stages.

Summary of Results

We demonstrate that Dolly Varden have become increasingly mismatched with spring downstream migrations of abundant pink salmon (Oncorhynchus gorbuscha) juveniles. However, Dolly Varden have remained matched with fall upstream migrations of spawning Pacific salmon, including coho (Oncorhynchus kisutch), sockeye (Oncorhynchus nerka), and pink salmon. Downstream predator–prey migration synchrony decreased over time and with higher temperatures, particularly with pink salmon. In contrast, upstream migration synchrony was temporally stable and increased with rising temperatures.

Differing trends in Dolly Varden predator–prey synchrony may be explained by the direct use of salmon to cue upstream migration, but not downstream migration. Overall, we show that climate change can have differing impacts on predator–prey synchrony across life-history stages.