title: Mechanisms of plant-plant interactions: concealment from herbivores is more important than abiotic-stress mediation in an African savannah.
abstract: Recent work on facilitative plant-plant interactions has emphasized the importance of neighbours' amelioration of abiotic stress, but the facilitative effects of neighbours in reducing plant apparency to herbivores have received less attention. Whereas theory on stress reduction predicts that competition should be more important in less stressful conditions, with facilitation becoming more important in harsh environments, apparency theory suggests that facilitation should be greater in the presence of herbivores, where it is disadvantageous to be conspicuous regardless of abiotic stress level. We tested the relative strength of neighbours' stress reduction versus apparency reduction on survival, growth, reproduction and lifetime fitness of Hibiscus meyeri, a common forb in central Kenya, using neighbour removals conducted inside and outside large-herbivore exclosures replicated in arid and mesic sites. In the absence of herbivores, neighbours competed with H. meyeri in mesic areas and facilitated H. meyeri in arid areas, as predicted by stress-reduction mechanisms. By contrast, neighbours facilitated H. meyeri in the presence of herbivory, regardless of aridity level, consistent with plant apparency. Our results show that the facilitative effects arising from plant apparency are stronger than the effects arising from abiotic stress reduction in this system, suggesting that plant-apparency effects may be particularly important in systems with extant large-herbivore communities.
authors: Environmental Studies Program, University of Colorado at Boulder, , Boulder, CO 80309, USA, Mpala Research Centre, , PO Box 555, Nanyuki 10400, Kenya, Program in Ecology, Department of Botany, University of Wyoming, , Laramie, WY 82070, USA, Program in Ecology, Department of Zoology and Physiology, University of Wyoming, , Laramie, WY 82070, USA, Department of Biology, University of Florida, , Gainesville, FL 32611, USA, Department of Ecology and Evolutionary Biology, Princeton University, , Princeton, NJ 08544, USA.
authors: Allison M
authors: AM
authors: Louthan
authors: Daniel F
authors: DF
authors: Doak
authors: Jacob R
authors: JR
authors: Goheen
authors: Todd M
authors: TM
authors: Palmer
authors: Robert M
authors: RM
authors: Pringle
mesh_terms: D002980:Climate; D004777:Environment; D060434:Herbivory; D007630:Kenya; D018521:Plant Physiological Phenomena; D011156:Population Density; D011157:Population Dynamics; D013312:Stress, Physiological
keywords: abiotic stress; facilitation; herbivory; plant apparency; stress-gradient hypothesis