Helena Maura Torezan-Silingardi

Loss and gains in ant–plant interactions mediated by extrafloral nectar: fidelity, cheats, and lies

All mutualistic plant–animal interactions are mediated by costs and benefits in relationships where resources (from plants) are exchanged by services (from animals). The most common trading coin that plants offer to pay for animal services is nectar; the main servers are hymenopterans. Extrafloral nectar (EFN) is produced in almost all aboveground plant parts not directly related with pollination, and their true function has long been an issue of discussion among naturalists and will be our main subject. The protective function of extrafloral nectaries (EFNs) is reviewed and considered with an alternative hypothesis, presenting not only ants, but also spiders and wasps as potential and effective agents in these protective interactions. Despite their likely relevance, the phenological variation (mainly sequential flowering and resprouting) of host plants mediating these interactions have been generally ignored. We discuss how the outcomes of each ant–EFN bearing plant interaction vary depending on physical and biotic changes in interacting organisms (internal factors such as phenology and species identity) as well as in their environments (external factors such as climatic variation), all of which may modify the character of each interaction. We propose that ant–EFN bearing plant interactions serve an excellent and unique model to test the “Geographic Mosaic Theory” of coevolution providing us a more clear view of how evolution has structured these plant–animal ecological networks.

Foraging behavior of Brachygastra lecheguana (Hymenoptera: Vespidae) on Banisteriopsis malifolia (Malpighiaceae): Extrafloral nectar consumption and herbivore predation in a tending ant system

In the Brazilian savanna many plant species bear regular associations with patrolling ants that are aggressive towards insect herbivores. However, not only ants but also several species of predatory wasps are attracted to plants due to the extrafloral nectaries (EFNs). Such wasps feed on both herbivores and plant exudates. In this study we describe the foraging behavior of the social Polistinae wasp Brachygastra lecheguana in the extrafloral nectaried shrub Banisteriopsis malifolia, and investigated the influence of patrolling ants Camponotus blandus on the activity of the wasp. Brachygastra lecheguana fed on the endophytic larvae of Anthonomus (Curculionidae) beetles that developed inside flower buds. The wasp lacerated the bud layers to reach the beetle larvae located at the bud core. The wasp visits to Ba. malifolia were statistically related to the abundance of flower buds and beetles. Ant exclusion experiments revealed that the hunting behavior of B. lecheguana on beetles was not related to the absence of C. blandus. However we found that wasps spent more time consuming extrafloral nectar on branches where ants were excluded. This is the first study reporting extrafloral nectar consumption by B. lecheguana, as well as the predation on herbivores in natural areas. In cerrado vegetation, ants benefit the plant by reducing insect herbivores, and our study provides evidence that the B. lecheguana – Ba. malifolia system represents a potential interaction where the wasp may also benefit the host plant. The value of this wasp species as a plant‐guard is discussed.

Ant–herbivore interactions in an extrafloral nectaried plant: are ants good plant guards against curculionid beetles?

Extrafloral nectary drinking ants are known as effective plant guards, but some herbivores may circumvent ant attacks by foraging on different plant parts or presenting adaptations to avoid ant predation. Here we experimentally investigated the effect of Camponotus blandus on the florivory of the extrafloral nectaried shrub Banisteriopsis malifolia; and a possible spatial segregation between ants and herbivores (leaves and flowers). Flower buds are attacked by Anthonomus weevils. Results revealed no significant influence of C. blandus on the reduction of florivory. Adult Anthonomus are hard-bodied and were immune to ant bites; larvae are endophytic, so protected from ants. Ants and adult beetles were concentrated in different plant parts (leaves and flowers, respectively) so restraining the probability of encounters. Our results indicate that the system C. blandus–Anthonomus–B. malifolia is not stable, as ants receive extrafloral nectar, but are unable to protect the plant against weevils.

Beneficial Effects of Ants and Spiders on the Reproductive Value of Eriotheca gracilipes (Malvaceae) in a Tropical Savanna

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.

Temporal niche overlap and distinct bee ability to collect floral resources on three species of Brazilian Malpighiaceae

Spatial and temporal limited resource and niche overlap studies have been widely used to explain resource-sharing in community ecology. Furthermore, morphological and behavioral differences among species are relevant to predict how they may share niche availabilities. We evaluated temporal niche overlap and the ability of visitors to collect floral resources on three Malpighiaceae species in the Brazilian savannah. We hypothesized: (I) an overlap between the temporal niches due the similarities between their floral resources requirements and the temporal limitation of flowering; and (II) a differential ability of bee species in resource harvesting. The 31 floral visitor species exhibited a higher niche overlap than expected by chance, confirming our first hypothesis. Furthermore, according to our second hypothesis, we observed that floral visitors showed a different efficiency in resource collection, depending on bee size and behavior. We believe that this may be a proxy of pollination efficiency. Our discussion is based on the distinct specialization of oil-collecting abilities and the specific requirements of each bee tribe.

The Complex Ant–Plant Relationship Within Tropical Ecological Networks

The tools involved in the study of ecological networks are relatively new and very useful to improve the knowledge about communities, biodiversity, and their conservation. In many tropical habitats, ants form the major part of the arthropod fauna found on vegetation and, therefore, it is extremely common to observe ants establishing ecological interactions with the host plants, where they find and use nectar, oils, pollen, arils, and seeds as food resources. In this chapter, we show that ant–plant interactions are dynamic, diverse, worldwide spread, and very manipulative which fit perfectly as models in studies dealing with interaction networks. For this, we have conducted global review in the distribution of studies on ant–plant networks and highlighted the most recurrent structural patterns observed in ant–plant networks and the main mechanisms and process behind this structure. Finally, we pointed out the limitations and new directions for the study of ant–plant networks in tropical environments.

Spiders as Plant Partners: Complementing Ant Services to Plants with Extrafloral Nectaries

In terrestrial communities, multitrophic interactions comprise a minimum of three trophic levels that interact among each other: plants, herbivores and their natural enemies. The top-down forces exerted by invertebrate predators on herbivores, and their cascading effect on plants, are very important to community structuring. Among major invertebrate predators, ants exert a strong impact on the density and spatial distribution of leaf and floral herbivores, which is reflected in the reproductive capacity of the plants. This important effect has only recently also been attributed to spiders. Studies of trophic interactions involving spiders and their impacts on the vegetation have increased considerably in the last few years. This is to be expected, considering that spiders are present in almost all terrestrial environments and occur in higher abundance in vegetation-rich areas. Regarded as excellent predators, spiders also use plants as foraging substrates, exploring differences in the plant architecture and in prey-capture strategies. Furthermore, spiders commonly prey on insect herbivores, which can result in a great decrease in herbivory rates, benefiting the host plants. In this chapter we will explore the hypothesis that spiders increase the reproductive value of plants with extrafloral nectaries, complementing the services provided by ants.