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Spatial niches and coexistence: testing theory with tarweeds
Susan Harrison1, Howard Cornell, Kara A Moore
1Department of Environmental Science and Policy, University of California, Davis, California 95616, USA.
Ecology
|August 19, 2010
Summary
Plant coexistence relies on specific habitat needs, not just seed availability. Even with ample seeds and disturbance, one species struggled to thrive outside its native environment, supporting niche theory.
Area of Science:
- Ecology
- Plant community dynamics
- Spatial ecology
Background:
- Competitive coexistence is often linked to niche differentiation.
- Recent theories highlight roles of propagule supply and chance events (e.g., neutral theory, stochastic niche theory, spatial storage effect).
- Understanding factors limiting species invasion is key to community assembly.
Purpose of the Study:
- To investigate the influence of propagule supply and disturbance timing on plant coexistence.
- To determine why a dominant species (Holocarpha virgata) cannot invade habitats of two other species (Calycadenia pauciflora, Hemizonia congesta).
Main Methods:
- Experimental addition of Holocarpha seeds into Calycadenia and Hemizonia habitats.
- Simulated experimental disturbances at different times of the year.
- Monitoring Holocarpha seedling density, survival, adult size, and fecundity over three years.
Main Results:
- Holocarpha seedling densities were high in new habitats, but survival and reproduction were significantly reduced outside its native environment.
- Holocarpha persisted in new habitats for three years, with springtime disturbance promoting its expansion.
- Despite persistence, Holocarpha exhibited below-replacement fitness and minimal competitive impact on resident species outside its native habitat.
Conclusions:
- Results support a deterministic view of spatial niches, where species have specific habitat requirements for successful establishment and reproduction.
- Chance events and propagule supply can lead to transient populations, potentially making communities appear unsaturated.
- Habitat specialization, rather than solely propagule availability or disturbance, appears critical for competitive coexistence in this plant community.
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