Data from: Changing light conditions in pine rockland habitats affect the intensity and outcome of ant–plant interactions

Extrafloral nectar (EFN) mediates food-for-protection mutualisms between plants and ants. Such mutualisms exist within a complex web of biotic interactions, and in a framework provided by the abiotic environment. Both biotic and abiotic factors, therefore, affect the outcome of ant–plant interactions. We conducted an experiment to determine the effects of ant activity, and light intensity, on herbivory rates, growth, and reproductive fitness in Senna mexicana var. chapmanii, a perennial legume native to pine rockland habitats of south Florida. Forty plants were divided among four treatments in a factorial experimental design with two independent variables: ant activity and light intensity. Plants were divided equally between sunny and shady habitats, and ants were excluded from half of the plants in each habitat type. The presence of ants significantly reduced herbivory rates in S. chapmanii. In shaded habitats, the presence of ants had no effect on plant reproductive fitness, however, in sunny habitats plants with ants produced significantly more seeds over the duration of the 1-yr study. Ants represent an important biotic defense against herbivores in S. chapmanii; however, their effects on plant fitness are dependent on light conditions. Pine rockland habitats in south Florida have been widely destroyed or mismanaged. In fragments that remain, suppression of fire has led to increased canopy closure and shading of the understory. These changes will likely negatively impact plants that rely on ants for defense. We highlight the importance of conservation efforts to preserve the pine rocklands and the fire regimes on which they rely.

花外蜜腺（Extrafloral nectar, EFN）介导植物与蚂蚁间的“食物-保护”互利共生关系。此类互利共生关系嵌套于复杂的生物相互作用网络之中，并受非生物环境框架的约束。因此，生物与非生物因子共同影响蚁植相互作用的结局。我们开展了一项实验，以探究蚂蚁活动与光照强度对墨西哥决明查普曼变种（Senna mexicana var. chapmanii）的植食率、生长及繁殖适合度的影响。该物种为多年生豆科植物，原生分布于美国南佛罗里达的松岩生境中。本实验采用双因素析因设计，设置两个自变量——蚂蚁活动与光照强度，共包含四种处理组合，40株供试植物被随机分配至各处理组中。供试植物被平均分配至向阳与遮阴两种生境中，且每种生境类型下的半数植株均被排除蚂蚁访问。实验结果显示，蚂蚁的存在显著降低了S. chapmanii的植食率。在遮阴生境中，蚂蚁的存在对植物繁殖适合度无显著影响；但在向阳生境中，有蚂蚁访问的植株在为期1年的研究周期内结籽量显著更高。蚂蚁是S. chapmanii抵御植食者的重要生物防御因子，但其对植物适合度的影响依赖于光照条件。南佛罗里达的松岩生境已遭到大范围破坏或不当管理。在现存的生境片段中，火灾抑制措施导致林冠封闭度提升，林下植被受到更多遮阴。这些变化很可能对依赖蚂蚁提供防御的植物产生负面影响。我们强调需开展保护工作，以维持松岩生境及其依赖的火制度。