Interações multitróficas no gravatá-do-banhado (Apiaceae): um teste do papel protetivo das formigas

Abstract

The mutualistic interactions of ants are easily observable, manageable, sustained over time, and can be considered a model system to understand plant association and defense. One of the forms of anti-herbivory defense used by plants is the biotic defense, which consists of the removal of herbivores by predators, indirectly protecting the plant. The main group involved in this defense are the ants, which in addition to protecting plants against their natural enemies and decreasing herbivory, receive food rewards. This protective role played by ants is present in several plant species, with plants that have specialized structures, some attractive mechanisms, or even that harbor hemipterans. The interaction that occurs between sucking hemipterans and ants is called trophobiosis. Trophobionts excrete a liquid food rich in sugars for the attendant ants. Another important feature of ant biology is the construction of anthills, which is a fundamental activity for several ecosystem services. This study aimed to evaluate the role of Camponotus termitarius in removing herbivores from Eryngium pandanifolium (swamp bowtie) plants near the nests. We also evaluated the relative role that the presence of trophobionts plays in this removal. The study was carried out in a rural region located in the Campus Capão do Leão of the Federal University of Pelotas, in themunicipality of Capão do Leão (southern Brazil). To evaluate the biotic defense in plants, according to proximity to nest and the influence of trophobionts, termites were used as a surrogate of potential herbivores. The biotic defense provided by the ants was evaluated through the behaviors observed in the interactions with termites in several types of response variables that were considered as (i) quantity of ants in the plant; (ii) number of touches by ants to termites; (iii) time elapsed until the first ring; (iv) amount of termite attack; (v) time elapsed until the first attack; (vi) number of termite removals and (vii) time elapsed until removal. From a total of 360 termites used, we recorded 259 interactions, divided into 53 touches, 128 attacks, and 78 removals, involving 214 ants of the species C. termitarius. Among the 60 plants in the experiment, 14 had the presence/interaction of C. rufipes, therefore they were excluded from some experiments, leaving 46 with the interaction of C. termitarius, of which 23 were closer to nests and 23 were far from nests. The results are consistent with the hypothesis that plants close to the nests receive greater protection from the ant C. termitarius against herbivory. Among nearby plants, the distance at which the nest is located is irrelevant for biotic defense. The effect of the presence of trophobionts in this scenario increases patrolling and recognition of possible threats to the plant but does not increase attacks.