Abstract
Variability in the size distributions of populations is usually studied in monocultures or in mixed plantings of two species. Variability of size distributions of populations in more complex communities has been neglected. The effects of seeding density (35 or 350 seeds/species/m2) and presence of small vertebrates on the variability of size distributions were studied for a total of 1,920 individuals of 4 species in replicated synthetic communities of 18 species in northern Illinois. End-of season height and above-ground biomass were measured for prairie perennials Dalea purpurea (purple prairie clover), Echinacea purpurea (purple coneflower), Desmanthus illinoensis (Illinois bundleflower) and Heliopsis helianthoides (early sunflower). Variability in biomass distribution of the four target species was twice as great at low than at high densities when small vertebrates were excluded. Our results suggest that inter- and intraspecific competition may affect all individuals more under high-density conditions, thereby reducing the variability in their biomass distributions within this community. This result, a consequence of plant-plant interaction, is obscured when small birds or mammals are present, presumably because either or both add variance that overwhelms the pattern.
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Acknowledgements
We are grateful for the enthusiastic support of Kris Bachtelle, Christopher Dunn and Duane Henry of the Morton Arboretum. This study would have been impossible without many volunteers who helped establish the experiment. We are especially grateful to J. Fornoni, J. Klock, R. Mazurek, L. Pitelka, G. Nuñez, H. Stevens, A. Sullivan, J. Weiner, B. Zorn-Arnold and one anonymous reviewer for comments on the manuscript. C. Martínez-Garza was supported by a fellowship from the National Council of Science and Technology of Mexico (CONACyT). The work was partially supported by the National Science Foundation (USA) and the University of Illinois.
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Martínez-Garza, C., Saha, S., Torres, V. et al. Planting densities and bird and rodent absence affect size distributions of four dicots in synthetic tallgrass communities. Oecologia 139, 433–439 (2004). https://doi.org/10.1007/s00442-004-1521-7
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DOI: https://doi.org/10.1007/s00442-004-1521-7