Priority Effects and Nonhierarchical Competition Shape Species Composition in a Complex Grassland Community

Area of Science:

• Ecology
• Community Ecology
• Invasion Biology

Background:

• Niche and fitness differences are key to understanding competition outcomes.
• Determining their relative importance in invaded, non-equilibrium communities is challenging.
• Classic pairwise competition models may not fully capture complex species assemblages.

Purpose of the Study:

• To investigate the relative importance of niche and fitness differences in invaded grassland communities.
• To assess the applicability of classic competition models to complex species assemblages.
• To model the dynamics of native and exotic species interactions.

Main Methods:

• Parameterized a population-dynamic model.
• Utilized competition experiments involving two native and three exotic grassland species.
• Simulated community dynamics under various competition scenarios.

Main Results:

• Native species showed minimal fitness or niche differences, resulting in slow dynamics and priority effects.
• Exotic species possessed large fitness advantages, enabling unconditional invasion.
• Priority effects among exotic species led to single-species dominance in 80% of model outcomes.
• Fungal infection had minimal impact on coexistence.

Conclusions:

• Invaded communities may be governed by nearly neutral dynamics and priority effects.
• Classic pairwise competition approaches may be insufficient for predicting outcomes in complex invaded systems.
• Priority effects, particularly between exotic species, are significant drivers of community composition.