Trait-mediated indirect interactions in invasions: unique behavioral responses of an invasive ant to plant nectar

Abstract

Abstract. Exotic species often form beneficial, facultative associations with indigenous species.However, we still have a limited understanding of the influences that these positive associations may have on the dynamics and impacts of species invasions. Highly invasive species may respond differently than less invasive species to resources that are exchanged in mutualisms, leading to trait-mediated indirect interactions between native species via invaders that may reshape native communities. In this study, we tested the hypothesis that the highly invasive ant species, Anoplolepis gracilipes, exhibits stronger trait changes in response to increasing levels of nectar than co-occurring, less invasive ant species. Across two islands in the Samoan Archipelago, we located multiple sites dominated by A. gracilipes and multiple sites dominated by other, less invasive species. At each site, we manipulated nectar levels on a common extrafloral nectary-bearing shrub and assessed short-term changes in ant worker recruitment and aggression. We found that the recruitment response of the highly invasive ant species A. gracilipes was not unique: other dominant ant species also increased recruitment in response to increasing nectar levels. However, A. gracilipes did show unique changes in aggressive behaviors: as nectar levels increased, the proportion of prey discovered, attacked and removed by A. gracilipes workers and the speed at which they performed these aggressive behaviors all increased strongly. Other ant species showed no such responses. In addition, fewer subordinate ants persisted on plants at sites invaded by A. gracilipes. Finally, plot-level, simultaneous manipulations of ant access to the plants and nectar availability demonstrated that Morinda citrifolia-ant mutualisms influenced the b-diversity of local arthropod communities differently when A. gracilipes dominated local ant assemblages. These results suggest that mutualisms between invasive ants and native plants can modify interactions between invaders and co-occurring arthropods, possibly leading to more negative consequences for native communities. They also underscore the importance of incorporating both positive species interactions and indirect pathways into our studies of both community ecology and invasion biology.

Carbohydrate scarcity increases foraging activities and aggressiveness in the ant Prolasius advenus (Hymenoptera: Formicidae)

“…This hypothesis has been supported by several field and laboratory studies (Yanoviak & Kaspari, ; Gibb & Cunningham, ; Kay et al ., ; Kaspari et al ., ). Interestingly, such a pattern was also found in several invasive ants, whose foragers were more abundant or more aggressive when given access to increased carbohydrate resources in field experiments (Rowles & Silverman, ; Savage & Whitney, ). Overall, the variety of responses described so far thus makes it difficult to predict how any given species will react when faced with varying carbohydrate or food availabilities.…”

“…A number of studies have examined how different contexts of nutrient availability and their effects at the individual, colony, population and community levels may favor or prevent the ability of an introduced ant species to maintain and expand in a new environment. For example, increased carbohydrate availability was found to increase aggression towards prey in the yellow crazy ants, Anoplolepis gracilipes (Savage & Whitney, ), but to decrease aggressiveness towards ant competitors in the Caribbean crazy ants, Nylanderia fulva (Horn et al ., ). Nutrient imbalances were shown to affect colony growth and induce dietary manipulation of hoarded food in fire ants, Solenopsis invicta (Cook et al ., ; Wilder et al ., ), and to influence foraging activity and competitive performance in the Argentine ant Linepithema humile (Grover et al ., ; Sagata & Lester, ; Kay et al ., ).…”

“…Nutrient imbalances were shown to affect colony growth and induce dietary manipulation of hoarded food in fire ants, Solenopsis invicta (Cook et al ., ; Wilder et al ., ), and to influence foraging activity and competitive performance in the Argentine ant Linepithema humile (Grover et al ., ; Sagata & Lester, ; Kay et al ., ). An important result emerging from this growing body of work is that ants' invasiveness may depend, in part, on their ability and tendency to respond strongly to carbohydrate availability (Rowles & Silverman, ; Savage & Whitney, ; Savage et al ., ; Shik & Silverman, ).…”

Previous diet affects the amount but not the type of bait consumed by an invasive ant

“…Even if we did diminish available protein substantially, the preference for baits with sugar may be due to a preference for an especially high carbohydrate‐biased diet in this species. Yellow crazy ants are a ‘high tempo’ ant renowned for their attraction to naturally occurring carbohydrate‐rich resources in the environment . The similarly invasive Argentine ant ( Linepithema humile ) had greater colony growth when maintained on a diet of either 6:1 or 3:1 carbohydrate:protein (C:P) than on lower C:P ratio diets .…”

High invasive ant activity drives predation of a native butterfly larva

“…Carbohydrate‐rich resources, such as honeydew and floral and extrafloral nectar (EFN), attract ants onto plants and may mediate their activity and interspecific competitive ability (Grover et al . ; Savage & Whitney ). While foraging on these resources, ants may disrupt plant–insect interactions by attacking or deterring pollinators (Lach , LeVan et al .…”