We tested the interactive effects of top-down (mite herbivores and predators) and bottom-up (fertilization) factors on cottonwood sapling performance, measured as leaf area, number of leaves, and height growth rate. Herbivorous spider mites in the absence of predators reduced plant performance on both fertilized and unfertilized plants. Plants responded to fertilization with increased growth only in the absence of herbivores. Without fertilization, plant performance with herbivores and predators present exceeded that of control plants with no herbivore damage. With fertilization, plant performance was intermediate between plants with herbivores and plants without herbivores or predators. By four weeks predators had effectively removed herbivorous mites on fertilized and unfertilized plants. Predator populations were unaffected by fertilization but significantly reduced herbivore populations more on fertilized than unfertilized plants. The results suggest that plant performance depends on the complex interaction between top-down and bottom-up factors.
Oikos is a journal issued by the Nordic Ecological Society and is one of the leading peer-reviewed journals in ecology. Oikos publishes original and innovative research on all aspects of ecology. Emphasis is on theoretical and empirical work aimed at generalization and synthesis across taxa, systems and ecological disciplines. Papers should be well founded in ecological theory and contribute to new developments in ecology by reporting novel theory or critical experimental results. Confirming or extending the established literature is given less priority. Synthesis of new and emerging fields in ecology and beyond is encouraged. Papers of review character should should strive for conceptual unification and being a point of departure for future work rather that restrospective summaries of established fields or topics.
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