@article{685510fcedd64a168904178e07fd6ca8,
title = "Good neighbors make good defenses: associational refuges reduce defense investment in African savanna plants",
abstract = "Intraspecific variation in plant defense phenotype is common and has wide-ranging ecological consequences. Yet prevailing theories of plant defense allocation, which primarily account for interspecific differences in defense phenotype, often fail to predict intraspecific patterns. Furthermore, although individual variation in defense phenotype is often attributed to ecological interactions, few general mechanisms have been proposed to explain the ubiquity of variable defense phenotype within species. Here, we show experimentally that associational refuges and induced resistance interact to create predictable intraspecific variation in defense phenotype in African savanna plants. Physically defended species from four families (Acanthaceae, Asparagaceae, Cactaceae, and Solanaceae) growing in close association with spinescent Acacia trees had 39–78% fewer spines and thorns than did isolated conspecifics. For a subset of these species, we used a series of manipulative experiments to show that this variability is maintained primarily by a reduction in induced responses among individuals that seldom experience mammalian herbivory, whether due to association with Acacia trees or to experimental herbivore exclusion. Unassociated plants incurred 4- to 16-fold more browsing damage than did associated individuals and increased spine density by 16–38% within one month following simulated browsing. In contrast, experimental clipping induced no net change in spine density among plants growing beneath Acacia canopies or inside long-term herbivore exclosures. Associated and unassociated individuals produced similar numbers of flowers and seeds, but seedling recruitment and survival were vastly greater in refuge habitats, suggesting a net fitness benefit of association. We conclude that plant-plant associations consistently decrease defense investment in this system by reducing both the frequency of herbivory and the intensity of induced responses, and that inducible responses enable plants to capitalize on such associations in heterogeneous environments. Given the prevalence of associational and induced defenses in plant communities worldwide, our results suggest a potentially general mechanism by which biotic interactions might predictably shape intraspecific variation in plant defense phenotype.",
keywords = "Acacia, African savannas, associational defense, associational resistance, defense priming, facilitation, herbivory, induced response, inducible defense, physical plant defenses, spines, thorns",
author = "Coverdale, {Tyler C.} and Goheen, {Jacob R.} and Palmer, {Todd M.} and Pringle, {Robert M.}",
note = "Funding Information: We thank the government of Kenya (NACOSTI/P/14/8746/1626), D. Martins, and Mpala Research Centre and Conservancy for permission to conduct this study. J. Abolem, V. Amaral, C. Clements, B. Culver, J. Echekan, A. Garr, K. Grabowski, A. Hassan, A. Ibrahim, A. Iqbal, S. Kurukura, A. Marsh, I. McGeary, M. Mohamed, J. Mosiany, P. Nasikie, and R. O{\textquoteright}Connell assisted with field work. We thank J. Atkins, D. Augustine, M. Bertness, G. Charles, J. Daskin, J. Guyton, L. Hedin, M. Hutchinson, T. Kartzinel, S. Levin, A. Louthan, J. Metcalf, S. Pacala, A. Potter, D. Rubenstein, C. Tarnita, J. Witman, T. Young, and two anonymous reviewers for conversation and insightful comments on the manuscript. T. C. Coverdale was supported by an NSF Graduate Research Fellowship, an NSF Doctoral Dissertation Improvement Grant (DEB-1601538), a Lewis and Clark Fund for Exploration and Field Research grant from the American Philosophical Society, a Princeton Institute for International and Regional Studies Summer Research Grant, and the Caroline Thorn Kissel Summer Environmental Studies Scholarship from the Garden Club of America. R. M. Pringle was supported by NSF DEB-1355122, DEB-1457691, and IOS-1656527, the Princeton Environmental Institute, and the Innovation Fund for New Ideas in the Natural Sciences from the Office of the Dean of Research of Princeton University. J. R. Goh-een was supported by NSF DEB-1457679 and DEB-1556728, and the University of Wyoming{\textquoteright}s Biodiversity Institute. T. M. Palmer was supported by NSF DEB-1149980. The UHURU experiment was built with a Natural Sciences and Engineering Research Council Tools and Instruments grant and funds from the University of Florida and the Sherwood Family Foundation. T. C. Coverdale conceived the research. T. C. Coverdale and R. M. Pringle designed the research plan. T. C. Coverdale performed the research and analyzed the data. J. R. Goheen, T. M. Palmer, and R. M. Pringle conceived and implemented the UHURU experiment. T. C. Coverdale wrote the manuscript with input from R. M. Pringle; all authors contributed edits and approved the final version. Funding Information: We thank the government of Kenya (NACOSTI/P/14/8746/1626), D. Martins, and Mpala Research Centre and Conservancy for permission to conduct this study. J. Abolem, V. Amaral, C. Clements, B. Culver, J. Echekan, A. Garr, K. Grabowski, A. Hassan, A. Ibrahim, A. Iqbal, S. Kurukura, A. Marsh, I. McGeary, M. Mohamed, J. Mosiany, P. Nasikie, and R. O'Connell assisted with field work. We thank J. Atkins, D. Augustine, M. Bertness, G. Charles, J. Daskin, J. Guyton, L. Hedin, M. Hutchinson, T. Kartzinel, S. Levin, A. Louthan, J. Metcalf, S. Pacala, A. Potter, D. Rubenstein, C. Tarnita, J. Witman, T. Young, and two anonymous reviewers for conversation and insightful comments on the manuscript. T. C. Coverdale was supported by an NSF Graduate Research Fellowship, an NSF Doctoral Dissertation Improvement Grant (DEB-1601538), a Lewis and Clark Fund for Exploration and Field Research grant from the American Philosophical Society, a Princeton Institute for International and Regional Studies Summer Research Grant, and the Caroline Thorn Kissel Summer Environmental Studies Scholarship from the Garden Club of America. R. M. Pringle was supported by NSF DEB-1355122, DEB-1457691, and IOS-1656527, the Princeton Environmental Institute, and the Innovation Fund for New Ideas in the Natural Sciences from the Office of the Dean of Research of Princeton University. J. R. Goheen was supported by NSF DEB-1457679 and DEB-1556728, and the University of Wyoming's Biodiversity Institute. T. M. Palmer was supported by NSF DEB-1149980. The UHURU experiment was built with a Natural Sciences and Engineering Research Council Tools and Instruments grant and funds from the University of Florida and the Sherwood Family Foundation. T. C. Coverdale conceived the research. T. C. Coverdale and R. M. Pringle designed the research plan. T. C. Coverdale performed the research and analyzed the data. J. R. Goheen, T. M. Palmer, and R. M. Pringle conceived and implemented the UHURU experiment. T. C. Coverdale wrote the manuscript with input from R. M. Pringle; all authors contributed edits and approved the final version. Publisher Copyright: {\textcopyright} 2018 by the Ecological Society of America",
year = "2018",
month = aug,
doi = "10.1002/ecy.2397",
language = "English (US)",
volume = "99",
pages = "1724--1736",
journal = "Ecology",
issn = "0012-9658",
publisher = "Ecological Society of America",
number = "8",
}