Density-dependent effects on group size are sex-specific in a gregarious ungulate

Area of Science:

• Ecology
• Behavioral Ecology
• Population Dynamics

Background:

• Density dependence significantly influences social behaviors, including group size in animal populations.
• Understanding sex-specific responses to density is crucial for predicting population dynamics and social structures.

Purpose of the Study:

• To investigate how changes in population density affect sex-specific group size in elk (Cervus canadensis).
• To determine if the observed changes in group size are density-dependent or frequency-dependent.

Main Methods:

• Quantified changes in elk group size and dispersion in response to experimentally reduced population densities (from 1.20 to 0.67 elk/km²).
• Analyzed sex-specific data from a Manitoba, Canada elk population between 2002 and 2009.

Main Results:

• Elk group size exhibited sex-specific functional responses to population density.
• Female elk displayed positive density dependence in group size at densities ≥0.70 elk/km², with evidence of a minimum group size at ≤0.70 elk/km².
• Male elk group size changes were density-dependent, but with a weaker relationship than females, primarily driven by solitary males joining groups.

Conclusions:

• Population density impacts male and female elk group sizes differently.
• These sex-specific responses have significant implications for ecological factors such as predation risk, resource competition, and mate access.