Seedling recruitment correlates with seed input across seed sizes: implications for coexistence

Area of Science:

• Ecology
• Plant Ecology
• Community Ecology

Background:

• Community assembly and diversity depend on plant recruitment dynamics.
• Theory suggests small-seeded species are microsite-limited and large-seeded species are seed-limited.
• Seed predation can disproportionately affect large-seeded species, influencing their establishment.

Purpose of the Study:

• To test predictions of recruitment limitation in perennial forbs varying in seed size.
• To assess the impact of postdispersal seed predation on recruitment functions.
• To investigate how spatial variation in grassland sites affects recruitment.

Main Methods:

• Compared recruitment functions of 16 perennial forb species with varying seed sizes.
• Manipulated seed densities from zero to three times natural fecundity in undisturbed plots.
• Conducted experiments across 10 grassland sites with differing productivity and resource availability.

Main Results:

• Most species exhibited linear recruitment functions, indicating seed limitation, contradicting the microsite limitation theory for small-seeded species.
• Recruitment functions saturated near average fecundity for only 19-37% of species, unrelated to seed size.
• Rodent seed predation strongly inhibited recruitment of large-seeded species but not small-seeded ones.
• Small-seeded species showed greater sensitivity to spatial variation in recruitment conditions across sites.
• Small-seeded species recruitment was more inhibited at productive sites compared to large-seeded species.

Conclusions:

• Plant recruitment is often seed-limited, even for highly fecund small-seeded species.
• Seed predation, particularly by rodents preferring larger seeds, can significantly increase seed limitation for large-seeded species.
• Understanding seed predation and spatial variation is crucial for predicting plant community assembly and species coexistence.