Phenological shifts can disrupt ecosystems by altering the timing and duration of species interactions. Most phenology research identifies phenological shifts by changes in the onset or mean of a phenological event, but these metrics ignore individual variation in timing (i.e., phenological synchrony), and therefore may be uninformative for predicting ecological effects of phenological shifts. Phenological synchrony should be ecologically important because it influences a population’s density through time, size structure, and temporal-numerical overlap with interacting populations. However, we currently know very little about how phenological synchrony contributes to population demography and species interactions. We addressed this gap with a mixed approach combining agent-based modelling and aquatic mesocosm experiments. In both approaches, we manipulated phenological synchrony and mean of a population in relation to its competitor and measured outcomes on population vital rates and competitive outcomes.
Results/Conclusions
Decreasing phenological synchrony increased population survival by as much as 10%. This effect was driven by low synchrony generating strong asymmetries among individuals (via age differences) that shifted intraspecific interactions from scramble to content competition, thereby more strongly allocating limited resources towards those individuals that survived. Additionally, in a competition context, arrival synchrony served as a bet-hedging strategy; low synchrony reduces the benefit of arriving earlier than a competing species but also reduces the cost of arriving later (14% reduction in survival at early arrival; 25% increase in survival at late arrival). Alternatively, high synchrony increases the benefit of early arrival, but also increases the cost of late arrival (5% increase in survival at early arrival; 8% reduction in survival at late arrival). Our results demonstrate it is critical to consider synchrony when measuring phenological shifts and predicting ecological outcomes. With climate change rapidly altering species phenologies, it is increasingly important to be able to accurately track phenological shifts and predict the net effects. We demonstrate that this requires expanding our traditional framework of phenological shifts to also include shifts in phenological synchrony.