Predator-prey feedback in a gyrfalcon-ptarmigan system?

Area of Science:

• Ecology
• Population Dynamics
• Time Series Analysis

Background:

• Specialist predators' population dynamics are influenced by prey, but they don't always cause prey cycles.
• Distinguishing top-down (predator-driven) from bottom-up (prey-driven) dynamics is crucial for understanding predator-prey coupling.
• Confounding factors like weather can affect population dynamics, complicating analysis.

Purpose of the Study:

• To infer the degree of coupling between gyrfalcon (Falco rusticolus) and rock ptarmigan (Lagopus muta) populations.
• To assess the influence of abiotic (weather) variables on these populations.
• To differentiate between top-down and bottom-up predator-prey dynamics using time series models.

Main Methods:

• Utilized multivariate autoregressive (MAR) models with 1 and 2 time lags (MAR(1) and MAR(2)).
• Contrasted models assuming predator-prey feedback (top-down) versus prey-driven dynamics (bottom-up).
• Employed simulations to evaluate model identification accuracy and robustness.

Main Results:

• MAR(1) models suggested predator-prey feedback and weak weather effects on gyrfalcons.
• MAR(2) models allowed for independent cycling and suggested bottom-up scenarios, fitting data better but showing less realistic correlations.
• Simulations indicated MAR(1) top-down models are more prone to misidentification as bottom-up than vice versa.

Conclusions:

• Predator-prey feedback is the most likely driver of oscillations in the gyrfalcon-ptarmigan system.
• Bottom-up dynamics remain a possibility, requiring further investigation.
• Ecological time series analysis, enhanced by simulations, can improve understanding of complex ecological interactions and identify key drivers.