Differences in spatial versus temporal reaction norms for spring and autumn phenological events

Abstract

For species to stay temporally tuned to their environment, they use cues such as the accumulation of degree-days. The relationships between the timing of a phenological event in a population and its environmental cue can be described by a population-level reaction norm. Variation in reaction norms along environmental gradients may either intensify the environmental effects on timing (cogradient variation) or attenuate the effects (countergradient variation). To resolve spatial and seasonal variation in species’ response, we use a unique dataset of 91 taxa and 178 phenological events observed across a network of 472 monitoring sites, spread across the nations of the former Soviet Union. We show that compared to local rates of advancement of phenological events with the advancement of temperature-related cues (i.e., variation within site over years), spatial variation in reaction norms tend to accentuate responses in spring (cogradient variation) and attenuate them in autumn (countergradient variation). As a result, among-population variation in the timing of events is greater in spring and less in autumn than if all populations followed the same reaction norm regardless of location. Despite such signs of local adaptation, overall phenotypic plasticity was not sufficient for phenological events to keep exact pace with their cues—the earlier the year, the more did the timing of the phenological event lag behind the timing of the cue. Overall, these patterns suggest that differences in the spatial versus temporal reaction norms will affect species’ response to climate change in opposite ways in spring and autumn.

Phenological shifts of abiotic events, producers and consumers across a continent

“…In this context, we note that our current data include both abiotic climate-related events and biotic responses, with the former shifting more than the latter. These disparities between the rates of change in the abiotic environment and species responses match previous observations that current phenological plasticity is not keeping pace with variation in climatic conditions 3,17,18,22,[53][54][55][56] . Mismatches between the velocity of climate change and realised seasonal shifts may help identify regions of concern, e.g.…”

“…2 and Extended Data Fig. 2) importantly qualifies the expectation of a strong and general pattern of phenology change along latitudinal or other environmental gradients 17 . Yet, it is consistent with our previous work 17 showing that phenological plasticity is constrained by local differentiation in reaction norms to temperature cues 44 , i.e., by local adaptation (see also 18,45 ).…”

“…2) importantly qualifies the expectation of a strong and general pattern of phenology change along latitudinal or other environmental gradients 17 . Yet, it is consistent with our previous work 17 showing that phenological plasticity is constrained by local differentiation in reaction norms to temperature cues 44 , i.e., by local adaptation (see also 18,45 ). Under such a scenario, we would indeed expect site-specific variation in phenology beyond patterns attributable to average temperature or its change over time.…”

“…On top of species-specific variation, there is also considerable site-specific variation in phenological advance 16 . Such variation among sites and populations may arise from a combination of factors, including changes in temperature and other climatic variables, population sizes, genetic differences, phenotypic plasticity, and land use 16,17 .…”

“…As proposed by Burrows et al 17,52 , the observed patterns of shifts in phenology should be compared to patterns in the velocity and seasonal shift of climate change. In this context, we note that our current data include both abiotic climate-related events and biotic responses, with the former shifting more than the latter.…”