A density-dependent model of Cirsium vulgare population dynamics using field-estimated parameter values

Area of Science:

• Ecology
• Population Biology
• Mathematical Modeling

Background:

• Population dynamics are influenced by density-dependent factors.
• The specific life-history stage where density dependence operates can significantly alter population trajectories.

Purpose of the Study:

• To develop and compare two stage-structured models of Cirsium vulgare population dynamics.
• To investigate the impact of density dependence at different life-history stages (germination vs. seedling) on population dynamics.
• To estimate density-dependent parameters from field data.

Main Methods:

• Development of two stage-structured population models for Cirsium vulgare.
• Incorporation of density dependence at either the germination stage (Version 1) or seedling stage (Version 2).
• Estimation of model parameters using annual census data from a factorial grazing experiment.

Main Results:

• Version 1 (germination density dependence) yielded significant parameter estimates and predicted two-point limit cycles under hard grazing.
• Limit cycles were most pronounced at the early rosette stage.
• Version 1 accurately predicted mean plant density across grazing treatments (r²=0.81).

Conclusions:

• The stage at which density dependence operates critically influences predicted population dynamics.
• Accurate identification of density-dependent stages is essential for reliable ecological modeling.
• Arbitrarily assigning density dependence to life-history stages can lead to erroneous predictions.