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Plants allocate defences in order to decrease costs and maximize benefits against herbivores. The Optimal Defense Theory (ODT) predicts that continuously expressed (i.e. constitutive) defences are expected in structures of high value, whereas defences that are expressed or that increase their expression only after damage or upon risk of damage (i.e. induced defences) are expected in structures of low value. Although there are several studies evaluating ODT predictions, few studies have successfully tested them as a way of measuring ecological investment in extrafloral nectary (EFN)‐mediated ant–plant interactions. Here we compared extrafloral nectar production and ant attractiveness to EFNs located on vegetative versus reproductive plant structures on Qualea multiflora plants subjected to different levels of simulated herbivory. We then addressed the following predictions emerging from the ODT: (a) extrafloral nectar produced in inflorescence EFNs will have higher volumes and calories and will attract more ants than extrafloral nectar produced in leaf EFNs; (b) extrafloral nectar production (volume and calories) and ant attendance will increase after simulated herbivory in leaf EFNs but not in inflorescence EFNs; (c) higher simulated leaf herbivory will induce higher extrafloral nectar production in EFNs on leaves and (d) more attractive extrafloral nectar (higher volume and calories) will attract more ants. Extrafloral nectar volume and calorie content, as well as ant abundance, were higher in EFNs of inflorescences compared to EFNs of leaves both before and after simulated herbivory, consistent with one of our predictions. However, EFNs on both leaves and inflorescences, not on leaves only, were induced by simulated herbivory, a pattern opposite to our prediction. Plants subjected to higher levels of leaf damage produced more and higher calorie extrafloral nectar, but showed similar ant abundance. Finally, more attractive extrafloral nectar attracted more ants. Synthesis. Our results show that extrafloral nectar production before and after simulated herbivory, as well as ant recruitment, varies according to the plant structure on which EFNs are located. Our study is the first to show that ant recruitment via extrafloral nectar follows predictions from Optimal Defense Theory, and that the ant foraging patterns may be shaped by the plant part attacked and the level of damage it receives.

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Predators affect plant fitness when they forage on them and reduce the action of herbivores. Our study evaluates the complementary effects of spiders and ants that visit the extrafloral nectaries of Eriotheca gracilipes (Malvaceae) on the production of fruits and viable seeds of these savanna trees. Four experimental groups were established: control group – with free access of spiders and ants; exclusion group – spiders and ants excluded; ant group – absence of spiders; and spider group – absence of ants. The presence of ants reduced the spider richness; however, the presence of spiders did not affect the ant richness. A significantly higher number of fruits per buds were found in the presence of spiders alone or spiders and ants together (control group) compared with the absence of both predators (exclusion group). The number of seeds per fruits and seed viability were higher in the control group. This is the first study showing that spiders and ants may exert a positive and complementary effect on the reproductive value of an extrafloral nectaried plant. Mostly the impact of ants and/or spiders on herbivores is considered, whereas our study reinforces the importance of evaluating the effect of multiple predators simultaneously, exploring how the interactions among predators with distinct skills may affect the herbivores and the plants on which they forage.

Background and Aims Ant–plant associations are widely diverse and distributed throughout the world, leading to complex ecological networks. Regarding ant–plant mutualism, ant pollination is a very rare interaction and few studies have shown the role of ants as pollinators. Therefore, we aimed to evaluate the role of ants as effective pollinators of Paepalanthus lundii (Eriocaulaceae) in a Brazilian savanna. Methods Fieldwork with experimental manipulation was conducted to evaluate the fitness of P. lundii, considering potential pollinators. For this, we mainly observed the number of seeds produced in different conditions: control, ant exclusion, exclusion of flying insects, and exclusion (entomophily test) of both ants and flying insects. Furthermore, we evaluated all floral visitors throughout the day, stigma receptivity, the numbers of male and female flowers, and patterns of species co-occurrence, which can indicate the presence of different pollinators in the plants at the same time. Key Results We observed a relation between seed production and ant visits; Camponotus crassus was the most frequent floral visitor and the most effective pollinator. Also, we observed a statistical difference between the numbers of male and female flowers produced, with a greater number of male flowers. Furthermore, P. lundii presented flowering asynchrony, with 12 different types of maturation sequence, which indicates a cross-pollination system. Lastly, we observed an overlap of the greatest abundance of C. crassus and the time of plant stigmatic receptivity, and a pattern of non co-occurrence of ants, which shows the pollinator role of this ant. Conclusions Our data provide evidence that previous generalizations neglecting the importance of ants as pollinators are wrong. Brazilian savanna can reveal a lot about the ant-pollination syndrome, since this environment presents peculiar characteristics related to this association. Thus, this study has great significance for the understanding of the ant-pollination syndrome, and for the understanding of the complex ecological networks present in these dry arid systems.