Dispersal: a matter of scale

Area of Science:

• Ecology
• Ornithology
• Conservation Biology

Background:

• Population density is often hypothesized to influence dispersal distances due to competition and aggression.
• Previous studies on density-dependent dispersal in long-lived vertebrates have produced inconsistent findings.
• Dispersal study conclusions can be sensitive to the spatial and temporal scales of analysis, yet multi-scale research is limited.

Purpose of the Study:

• To investigate the influence of population density on natal dispersal distances in a non-migratory Peregrine Falcon (Falco peregrinus) population.
• To examine these relationships across multiple spatial and temporal scales.
• To assess potential scale-dependency in the density-dispersal relationship.

Main Methods:

• Long-term study of Peregrine Falcons in the British Isles (1964-2016).
• Analysis of natal dispersal distances using ringed nestlings with subsequent recaptures or recoveries.
• Three distinct spatial scales were examined: a limited local area, a broader regional area, and the entire British Isles.

Main Results:

• Females consistently dispersed farther than males across all examined scales.
• A clear relationship between population density and dispersal distance was not found at the smallest study scale.
• A negative relationship between population density and dispersal distance emerged when analyzing data across the entire British Isles, indicating scale-dependent effects.

Conclusions:

• The relationship between population density and dispersal distance in Peregrine Falcons is strongly dependent on the spatial scale of analysis.
• Findings suggest that localized studies may not capture the full impact of density on dispersal, while broader analyses reveal significant patterns.
• Emphasizes the critical importance of considering both spatial and temporal scales when interpreting density-dependent dispersal hypotheses in long-lived species.