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

Area of Science:

• Ecology
• Evolutionary Biology
• Phenology

Background:

• Species rely on environmental cues, like degree-days, to synchronize phenological events with seasons.
• Population-level reaction norms describe the relationship between phenological timing and environmental cues.
• Variation in reaction norms can either amplify (cogradient) or dampen (countergradient) cue effects on timing.

Purpose of the Study:

• To investigate spatial and seasonal variation in species' phenological reaction norms.
• To understand how cogradient and countergradient variation influence species' temporal tuning to the environment.
• To assess if phenotypic plasticity is sufficient for phenological events to keep pace with environmental cues.

Main Methods:

• Utilized a unique dataset of 91 taxa and 178 phenological events.
• Data collected from 472 monitoring sites across the former Soviet Union.
• Compared spatial variation in reaction norms with temporal variation (within-site, year-to-year).

Main Results:

• Spatial variation in reaction norms accentuates spring phenological responses to temperature cues (cogradient).
• Spatial variation attenuates autumn phenological responses (countergradient).
• Phenological events lag behind cues in earlier years, indicating insufficient plasticity.

Conclusions:

• Spatial and temporal reaction norms influence species' responses to climate change differently in spring and autumn.
• Among-population variation in timing is greater in spring and lesser in autumn due to spatial reaction norm variation.
• Local adaptation through reaction norms exists but is insufficient to fully track rapid environmental changes.