Global shifts in the phenological synchrony of species interactions over recent decades

Abstract

Phenological responses to climate change (e.g., earlier leaf-out or egg hatch date) are now well documented and clearly linked to rising temperatures in recent decades. Such shifts in the phenologies of interacting species may lead to shifts in their synchrony, with cascading community and ecosystem consequences. To date, single-system studies have provided no clear picture, either finding synchrony shifts may be extremely prevalent [Mayor SJ, et al. (2017) Sci Rep 7:1902] or relatively uncommon [Iler AM, et al. (2013) Glob Chang Biol 19:2348-2359], suggesting that shifts toward asynchrony may be infrequent. A meta-analytic approach would provide insights into global trends and how they are linked to climate change. We compared phenological shifts among pairwise species interactions (e.g., predator-prey) using published long-term time-series data of phenological events from aquatic and terrestrial ecosystems across four continents since 1951 to determine whether recent climate change has led to overall shifts in synchrony. We show that the relative timing of key life cycle events of interacting species has changed significantly over the past 35 years. Further, by comparing the period before major climate change (pre-1980s) and after, we show that estimated changes in phenology and synchrony are greater in recent decades. However, there has been no consistent trend in the direction of these changes. Our findings show that there have been shifts in the timing of interacting species in recent decades; the next challenges are to improve our ability to predict the direction of change and understand the full consequences for communities and ecosystems.

Keywords: baseline; global warming; mismatch; time series; trophic interactions.

Fig. 1.

Changes in the relative timing of interacting species (n = 54). (A) The magnitude of synchrony change (days/decade) across interactions, with zero indicating no change in synchrony. Presented are the species-level intercepts (α_s) from the intercept-only model. The solid vertical line denotes the mean synchrony change (μ_α = 6.1 days/decade; 95% CI: 5.2, 7.0). The distribution in red represents the null model, with the dashed line as the mean synchrony change (μ_α = 0.97 days/decade; 95% CI: 0.96, 0.98). (B) Phenological change (days/decade) across interacting species. Interactions are ordered top to bottom by the magnitude of synchrony change. Numbers on the y axis represent their unique identifier in the analysis. Means with 95% CIs are shown. To improve viewing, overlapping labels have been removed. (C) The direction and magnitude of synchrony change (days/decade) across interactions, where positive values indicate that the timing of interacting species is getting closer together in the season (days) and negative values mean that the timing of interacting species is getting further apart in the season (days). Presented are the species-level intercepts (α_s) from the intercept-only model. The solid vertical line denotes the mean synchrony change (μ_α = −0.50 days/decade; 95% CI: −2.1, 1.1). The distribution in red represents the null model, with the dashed line as the mean synchrony change (μ_α = 0.048 days/decade; 95% CI: −0.08, 0.2).

Fig. 2.

Uncertainty in estimates of phenological and temperature change. (A) Relationship between phenological change (days/decade) and temperature change (°C/decade) across species (n = 37). Means with 95% CIs for both axes are shown. (B) Effect of time-series length (5–40 years, in increments of 5, assessed using a null model) on estimates of species’ phenological change (days/year) represented as black dots (n = 31), with 95% CIs represented by colored lines. Dotted lines bracket 20 years of data, corresponding to the average length of time series (mean = 21.7 years, SD = 8.4).