Coupling in goshawk and grouse population dynamics in Finland

Area of Science:

• Ecology
• Population Dynamics
• Wildlife Biology

Background:

• Predator-prey relationships are complex, influenced by prey species' traits and population densities.
• Forest grouse species (hazel, black, and capercaillie) are key prey for northern goshawks in Finland.
• Synchronous fluctuations in prey populations can complicate analyses of predator-prey dynamics.

Purpose of the Study:

• To model the population dynamics of northern goshawks and their main forest grouse prey in Finland.
• To assess the relative significance of individual prey species on goshawk population dynamics.
• To investigate the tightness of predator-prey coupling, considering density dependence, winter severity, and spatial correlation.

Main Methods:

• Utilized first-order log-linear vector autoregressive models.
• Analyzed long-term count data for northern goshawks (Accipiter gentilis) and three grouse species (1983-2010).
• Developed nine competing candidate models to test various combinations of prey effects on goshawk dynamics with lags of 1-3 years.

Main Results:

• Northern goshawk populations showed separate density effects from hazel grouse and black grouse, with lags of 1 and 3 years.
• Capercaillie had no discernible effect on goshawk populations, but goshawk presence negatively impacted capercaillie populations.
• Winter severity significantly affected both goshawk and hazel grouse populations negatively.

Conclusions:

• While large-scale goshawk-grouse population dynamics are coupled, individual species within the guild lack clear mutual effects.
• Pooling data from closely related, synchronously fluctuating prey species can lead to a loss of specific ecological information.
• Understanding species-specific interactions is crucial for accurate predator-prey modeling, even within a unified prey guild.