Evolutionary dynamics as a component of stage-structured matrix models: an example using Trillium grandiflorum

Area of Science:

• Ecology
• Evolutionary Biology
• Conservation Biology

Background:

• Demographic matrix models are standard for projecting population dynamics in conservation but typically exclude evolutionary processes.
• Natural selection can influence population fitness and long-term trajectories, yet its integration into demographic models remains a challenge.

Purpose of the Study:

• To project evolutionarily informed population trajectories for Trillium grandiflorum, a perennial plant facing decline from herbivory.
• To compare different methods of incorporating evolutionary selection into demographic models and assess their impact on projected population dynamics.

Main Methods:

• Developed deterministic matrix models incorporating selection analyses in three distinct ways.
• Compared these deterministic models with a more realistic individual-based model for projecting population trajectories.
• Analyzed selection on flowering time in Trillium grandiflorum, a trait linked to reduced herbivory by white-tailed deer.

Main Results:

• Deterministic models that averaged fitness over the phenotypic distribution yielded population trajectories similar to the individual-based model.
• A deterministic model using fitness at the mean phenotype projected a significantly faster rate of evolution than observed.
• Subtle differences in integrating evolutionary and demographic models can lead to substantial variations in predicted population outcomes.

Conclusions:

• Combining demographic and selection analyses is essential for understanding the role of evolution in population dynamics and persistence.
• The method chosen for integrating evolutionary dynamics into demographic models critically affects projections of population persistence.
• This research highlights the importance of considering evolutionary processes for accurate conservation planning.