Effects of plant age, experimental nutrient addition and ant occupancy on herbivory in a neotropical myrmecophyte

Abstract

Summary Variation in antiherbivore defences among individuals within a plant species may be influenced by intrinsic characteristics of the plant, environmental conditions and the interactions between these factors. We used a long‐term field experiment and a laboratory palatability trial to elucidate the effects of plant age, nutrient availability and ant occupancy on herbivore damage sustained by Cordia alliodora, a common neotropical myrmecophyte. Herbivory in this system was influenced by both plant characteristics and environmental conditions, and the relative importance of these variables changed with plant age. Five‐year‐old plants had a higher frequency of ant occupation and more workers per domatium than 1‐year‐old plants. Plant age did not significantly affect herbivory in either field studies or laboratory palatability trials conducted with a specialist herbivore. In the field, however, 1‐year‐old plants tended to have higher levels of herbivory than 5‐year‐old plants. There was a trend towards lower herbivory in trees that had been fertilized. Additionally, leaves from fertilized trees were significantly less palatable to specialist herbivores. In 1‐year‐old plants, the abundance of ants in domatia had no effect on herbivory of nearby leaves. In contrast, ant abundance and herbivory were negatively correlated for 5‐year‐old trees, demonstrating that ants provide effective defence only for older plants. These results suggest that understanding ant‐plant‐herbivore relationships requires examining how biotic and abiotic factors and their interactions change with plant ontogeny. Although our work focused on one particular ant‐plant system, the importance of ontogenetic variation in antiherbivore defence is increasingly recognized as a critical area of study in plant defence theory.