Landscape-scale eco-evolutionary dynamics: selection by seed predators and fire determine a major reproductive...

Area of Science:

• Ecology
• Evolutionary Biology
• Forest Science

Background:

• Eco-evolutionary dynamics significantly impact ecological processes, but their role in structuring natural ecosystems is less understood.
• Serotiny in lodgepole pine (Pinus contorta) influences postfire seedling density and ecosystem structure, traditionally viewed as an adaptation to fire.
• The selective pressure of seed predation on serotiny remains understudied.

Purpose of the Study:

• To investigate how eco-evolutionary dynamics, specifically the interplay between fire and seed predation, structure lodgepole pine ecosystems.
• To test the hypothesis that spatial variation in serotiny frequency results from conflicting selection pressures from fire and seed predation.
• To determine the relative influence of fire frequency and seed predator abundance on serotiny levels and subsequent forest structure.

Main Methods:

• Measured percentage serotiny in lodgepole pine cones across various sites in Yellowstone National Park.
• Quantified the abundance of American red squirrels (Tamiasciurus hudsonicus), a primary seed predator.
• Assessed forest structure and fire frequency (return intervals) at each study site.

Main Results:

• Fire frequency was a strong predictor of serotiny, consistent with existing literature.
• At high fire frequency sites, high squirrel abundance was negatively correlated with serotiny, indicating predation pressure can override fire selection.
• At low fire frequency sites, serotiny was consistently low (<10%). Forest structure predicted squirrel density, but serotiny did not explain additional variation, suggesting squirrels select against serotiny.

Conclusions:

• Eco-evolutionary dynamics, driven by the balance between fire and seed predation, significantly influence serotiny in lodgepole pine.
• Seed predation by squirrels can be a stronger selective force than fire in some contexts, leading to reduced serotiny.
• Forest structure is influenced by squirrel density, which is shaped by selection against serotiny, rather than squirrels adapting to serotiny levels.