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.
Data file for Dryad repository
Sheet 1 of the data file contains data describing plant growth rates. Column A identifies the individual plant. Column B show the light treatment (0=shade, 1=sun). Column C indicates ant treatment (0=ants present, 1-ants absent. Columns D through X are measurements of plant growth rate as an estimate of increased biomass over each 2 week period.
Sheet 2 of the data file contains data describing herbivory rates. Column A identifies the individual plant. Column B show the light treatment (0=shade, 1=sun). Column C indicates ant treatment (0=ants present, 1-ants absent. Columns D through X are measurements of plant herbivory rate as an estimate of % leaf area removal.
Sheet 3 of the data file contains data describing plant size. Column A identifies the individual plant. Column B show the light treatment (0=shade, 1=sun). Column C indicates ant treatment (0=ants present, 1-ants absent. Columns D through AB are measurements of plant size, taken as the total number of growing stems.
Sheet 4 of the data file contains data describing extrafloral nectar production. Column A identifies the individual plant. Column B show the light treatment (0=shade, 1=sun). Column C indicates ant treatment (0=ants present, 1-ants absent. Columns D through I are bi-monthly measurements of extrafloral nectar production, expressed as total sugar production from 5 leaves on each plant.
Sheet 5 of the data file contains data from insect surveys conducted throughout the year long study. Column A shows the date that surveys were conducted. Column B identifies the individual plant. Column C shows the light treatment (0=shade, 1=sun). Column D indicates ant treatment (0=ants present, 1-ants absent. Column E indicates whether the survey was conducted during the day or at night (0=day, 1=night). Columns F through AY are different insects and they presence and abundance are indicated for each survey.
Sheet 6 of the data file contains data describing plant reproductive fitness. Column A shows the date that data were collected. Column B identifies the individual plant. Column C shows the light treatment (0=shade, 1=sun). Column D indicates ant treatment (0=ants present, 1-ants absent. Columns E, F, G, and H indicate numbers of flowers, fruit set, mature fruit, and seeds respectively.
