Granivores and the Composition of Experimental Grass and Forb Communities

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9420860 Howe This study will examine whether seed-eating birds, and seed-eating and foliage-eating rodents influence community structure of tallgrass prairie. The objective is to determine whether predictable foraging behaviors have predictable consequences for composition and dominance in model tallgrass communities. To do so, the investigators will establish controlled communities of plant species stratified by seed size, form, and phenology. Plots protected from vertebrates should show dominance of large-seeded species and dicots. Plots accessible to rodents should show a depression in cover of seedlings of plant with seeds favored by rodents, while plots accessible to birds should show a depression in cover and seedlings of plant with seeds in their optimal handling range. Plots exposed to both will be dominated by species with the smallest, least desirable seeds. To refine predictions, the PIs will integrate censuses of vertebrate populations on and off the treatment plots with selectivity trials of common birds, mice, and voles on seeds or foliage of 12 plant species. Ranking of selectivities will determine whether seed preferences conform to predictions of foraging theory based on seed size and/or encounter rate. Rankings of seed and foliage selectivities will also provide specific predictions of how key animal species are likely to influence plant communities in the field. Concordant evaluation of on-site and off-site vertebrate populations will permit assessment of influences of treatments as compared with off-site effects of birds and mammals.