| Title: | Good neighbors make good defenses: associational refuges reduce defense investment in African savanna plants |
| Author(s): | Coverdale TC; Goheen JR; Palmer TM; Pringle RM; |
| Address: | "Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, 08544, USA. Department of Zoology & Physiology, University of Wyoming, Laramie, Wyoming, 82071, USA. Department of Biology, University of Florida, Gainesville, Florida, 32611, USA" |
| ISSN/ISBN: | 0012-9658 (Print) 0012-9658 (Linking) |
| 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 Animals Ecosystem *Grassland Herbivory Trees Acacia African savannas associational defense associational resistance defense priming facilitation induced response inducible defense physical plant defenses spines thorns; |
| Notes: | "MedlineCoverdale, Tyler C Goheen, Jacob R Palmer, Todd M Pringle, Robert M eng Research Support, N.I.H., Intramural Research Support, U.S. Gov't, Non-P.H.S. 2018/06/26 Ecology. 2018 Aug; 99(8):1724-1736. doi: 10.1002/ecy.2397. Epub 2018 Jun 25" |
