Phenological synchronization disrupts trophic interactions between Kodiak brown bears and salmon

Abstract

Climate change is altering the seasonal timing of life cycle events in organisms across the planet, but the magnitude of change often varies among taxa [Thackeray SJ, et al. (2016) 535:241-245]. This can cause the temporal relationships among species to change, altering the strength of interaction. A large body of work has explored what happens when coevolved species shift out of sync, but virtually no studies have documented the effects of climate-induced synchronization, which could remove temporal barriers between species and create novel interactions. We explored how a predator, the Kodiak brown bear (), responded to asymmetric phenological shifts between its primary trophic resources, sockeye salmon () and red elderberry (). In years with anomalously high spring air temperatures, elderberry fruited several weeks earlier and became available during the period when salmon spawned in tributary streams. Bears departed salmon spawning streams, where they typically kill 25-75% of the salmon [Quinn TP, Cunningham CJ, Wirsing AJ (2016) 183:415-429], to forage on berries on adjacent hillsides. This prey switching behavior attenuated an iconic predator-prey interaction and likely altered the many ecological functions that result from bears foraging on salmon [Helfield JM, Naiman RJ (2006) 9:167-180]. We document how climate-induced shifts in resource phenology can alter food webs through a mechanism other than trophic mismatch. The current emphasis on singular consumer-resource interactions fails to capture how climate-altered phenologies reschedule resource availability and alter how energy flows through ecosystems.

Body size and lean mass of brown bears across and within four diverse ecosystems

“…They are highly intelligent, diverse in their localized food habits and habitat use, and vary greatly in individual body size and population density (Pasitschniak‐Arts, ; Servheen, ; Leclerc et al ., ). Body size in brown bears is related to the quality, quantity, and availability of nutritional resources, especially protein (Hilderbrand et al ., ), though realized diet is shaped by macronutrient optimization and energy needs (Erlenbach et al ., ) and the availability of food resources that allow for optimization (Deacy et al ., ). Despite dietary plasticity indicating broad niche variation in nutritional resource utilization, the proportional fall body composition (i.e.…”

Warming counteracts defoliation‐induced mismatch by increasing herbivore‐plant phenological synchrony

“…In contrast, phenological shifts can also remove temporal barriers, synchronizing activities that were previously separated in time, and thereby establishing climate‐induced interactions (Kharouba et al, ). For example, during years of anomalously warm springs, brown bears switch their food preferences from salmon to elderberries, which usually mature several weeks earlier (Deacy et al, ). Such a shift in feeding alters the trophic network that is based on the ecological interaction between salmon and their predators (Helfield & Naiman, ).…”

Extreme winter warm event causes exceptionally early bud break for many woody species

“…) and altered phenology can disrupt ecological networks (Inouye 2008, Deacy et al. ). Since we measured trees and shrubs, long‐lived, modular organisms with stored energy that can survive organ damage or loss, all individuals survived the return of frost following this warm event.…”