Anisotropic patterned population synchrony in climatic gradients indicates nonlinear climatic forcing

Area of Science:

• Ecology
• Population Dynamics
• Climate Change Biology

Background:

• Spatial population synchrony is often attributed to climate (Moran effect), but disentangling climate impacts from other factors using survey data is challenging.
• Nonlinear population responses to climate variation complicate analysis but can also reveal climate impacts through specific survey designs.
• Species distribution ranges with consistent climate gradients (e.g., latitudinal, altitudinal) offer opportunities to study spatial synchrony patterns.

Purpose of the Study:

• To investigate how nonlinear population responses to climatic variation influence spatial synchrony patterns.
• To test the prediction that nonlinear climate impacts lead to anisotropic synchrony (direction-specific), dropping faster along than across climatic gradients.
• To exemplify a survey design and analysis approach for detecting climate-driven anisotropic synchrony.

Main Methods:

• Designing population surveys to strategically include altitudinal climatic gradients in subarctic birch forests.
• Comparing spatial synchrony patterns across and along the climatic gradient for two sympatric geometrid species.
• Analyzing population survey data to detect anisotropic synchrony patterns indicative of nonlinear climate sensitivity.

Main Results:

• One geometrid species (Operophtera brumata L.) exhibited anisotropic synchrony, consistent with a strong nonlinear sensitivity to climatic variation.
• The other sympatric geometrid species (Epirrita autumnata Bkh.) did not show anisotropic synchrony, suggesting a different response to climatic variation.
• The findings demonstrate the utility of gradient-based survey designs for identifying species with nonlinear climate responses.

Conclusions:

• Nonlinear population responses to climate can generate anisotropic spatial synchrony, detectable through gradient-based surveys.
• The study provides empirical evidence supporting the link between nonlinear climate sensitivity and directional population synchrony patterns.
• Understanding species-specific responses to climate is crucial for predicting population dynamics and ecological interactions in changing environments.