The indirect consequences of a mutualism: comparing positive and negative components of the net interaction between honeydew‐tending ants and host plants

Abstract

Summary1. In ecological webs, net indirect interactions between species are composed of interactions that vary in sign and magnitude. Most studies have focused on negative component interactions (e.g. predation, herbivory) without considering the relative importance of positive interactions (e.g. mutualism, facilitation) for determining net indirect effects. 2. In plant ⁄ arthropod communities, ants have multiple top-down effects via mutualisms with honeydew-producing herbivores and harassment of and predation on other herbivores; these ant effects provide opportunities for testing the relative importance of positive and negative interspecific interactions. We manipulated the presence of ants, honeydew-producing membracids and leaf-chewing beetles on perennial host plants in field experiments in Colorado to quantify the relative strength of these different types of interactions and their impact on the ant's net indirect effect on plants.3. In 2007, we demonstrated that ants simultaneously had a positive effect on membracids and a negative effect on beetles, resulting in less beetle damage on plants hosting the mutualism. 4. In 2008, we used structural equation modelling to describe interaction strengths through the entire insect herbivore community on plants with and without ants. The ant's mutualism with membracids was the sole strong interaction contributing to the net indirect effect of ants on plants. Predation, herbivory and facilitation were weak, and the net effect of ants reduced plant reproduction. This net indirect effect was also partially because of behavioural changes of herbivores in the presence of ants. An additional membracid manipulation showed that the membracid's effect on ant activity was largely responsible for the ant's net effect on plants; ant workers were nearly ten times as abundant on plants with mutualists, and effects on other herbivores were similar to those in the ant manipulation experiment. 5. These results demonstrate that mutualisms can be strong relative to negative direct interspecific interactions and that positive interactions deserve attention as important components of ecological webs.

Bears benefit plants via a cascade with both antagonistic and mutualistic interactions

“…In a previous study, ants had a negative net effect on plants due to the ant–treehopper mutualism and the treehopper's effect on plants (red paths) (Grinath et al . ). Interactions between non‐ant arthropod predators and herbivores are shown in grey to highlight paths that may be altered by intraguild predation.…”

Biodiversity and Ecosystem Functioning in Tropical Habitats — Case Studies and Future Perspectives in Atlantic Rainforest and Cerrado Landscapes

“…Although the above scenario may arise from the three trophic level interaction mentioned above, it has been suggested that ants may also repel chewing insects by consuming honeydew, decreasing their abundance and activity on plants [133]. The different responses of herbivores to abundance of ants found in our study suggest that the effect of ants on herbivores is dependent of herbivore feeding habits.…”

“…The different responses of herbivores to abundance of ants found in our study suggest that the effect of ants on herbivores is dependent of herbivore feeding habits. Several studies have reported non-obligatory interactions between ants and sap-sucking insects [123,[130][131][132][133][134]. In this interaction, ants feed on the honeydew and protect the insects against predators and competitors [130].…”

“…The outcome of the interaction between ants and plants may depend on feeding habits of the herbivores, due to the interaction between ants and sapfeeding insects. Several authors [123,[130][131][132][133][134] suggest that generalist ants feeding on their honeydew protect these insects from predators and competitors over chewing insects [130]. Moreover, plant protection may be related to ant species composition, as different ant species present varied behavior and defensive characteristics [129].…”

Tending-Ants Increase Survivorship and Reproductive Success of Calloconophora pugionata Drietch (Hemiptera, Membracidae), a Trophobiont Herbivore of Myrcia obovata O.Berg (Myrtales, Myrtaceae)

“…The study of community ecology, focused on negative interactions between species, has led to the neglect of positive interactions and its importance in food webs (Ohgushi, 2008;Grinath et al, 2012). The effect of Hemiptera-ant interaction can cause changes in community in terms of abun- dance, distribution and survival of the associated arthropods (Del-Claro & Oliveira, 2000;Renault et al, 2005;Styrsky & Eubanks, 2006).…”