Contrasting effects of an invasive ant on a native and an invasive plant

Abstract

When invasive species establish in new environments, they may disrupt existing or create new interactions with resident species. Understanding of the functioning of invaded ecosystems will benefit from careful investigation of resulting species-level interactions. We manipulated ant visitation to compare how invasive ant mutualisms affect two common plants, one native and one invasive, on a subtropical Indian Ocean island. Technomyrmex albipes, an introduced species, was the most common and abundant ant visitor to the plants. T. albipes were attracted to extrafloral nectaries on the invasive tree (Leucaena leucocephala) and deterred the plant's primary herbivore, the Leucaena psyllid (Heteropsylla cubana). Ant exclusion from L. leucocephala resulted in decreased plant growth and seed production by 22% and 35%, respectively. In contrast, on the native shrub (Scaevola taccada), T. albipes frequently tended sap-sucking hemipterans, and ant exclusion resulted in 30% and 23% increases in growth and fruit production, respectively. Stable isotope analysis confirmed the more predacious and herbivorous diets of T. albipes on the invasive and native plants, respectively. Thus the ants' interactions protect the invasive plant from its main herbivore while also exacerbating the effects of herbivores on the native plant. Ultimately, the negative effects on the native plant and positive effects on the invasive plant may work in concert to facilitate invasion by the invasive plant. Our findings underscore the importance of investigating facilitative interactions in a community context and the multiple and diverse interactions shaping novel ecosystems.

Are invasive ants better plant‐defense mutualists? A comparison of foliage patrolling and herbivory in sites with invasive yellow crazy ants and native weaver ants

“…EFNs or honeydew‐producing hemipterans), and prey are abundant on the ground, then A. gracilipes is unlikely to forage on the plant and protect it from herbivores (Lach 2003). Relationships between folivory and other invasive ant species attracted to facultatively ant‐associated plants by insects or nectar are similarly equivocal, with some studies showing declines in folivores or folivory on plants with invasive ants relative to no ants or other ants ( Linepithema humile : Koptur 1979; Technomyrmex albipes : Lach et al 2010; Solenopsis invicta : Stiles and Jones 2001, Ness 2003, Styrsky et al 2006), and others showing increases ( Pheidole megacephala : Djiéto‐Lordon et al 2004; Solenopsis invicta : Styrsky et al 2006).…”

“…Both focus on the red imported fire ant, Solenopsis invicta and their results are inconsistent; S. invicta provides greater protection from herbivores on some plant species (Stiles and Jones 2001, Ness 2003) but it has a net negative effect on others (Stiles and Jones 2001). Other invasive ant species are known to visit EFNs in some contexts ( Anoplolepis gracilipes : Lester and Tavite 2004, Savage et al 2009; Linepithema humile : Freitas et al 2000, Lach et al 2009; Pheidole megacephala : Lach et al 2009; Technomyrmex albipes , Lach et al 2010) but it is unknown how their herbivore‐deterring abilities compare to native ants. The high densities often achieved by invasive ants may translate to higher visitation rates to EFNs and better protection against herbivores.…”

Predicting novel herbivore–plant interactions

“…Several examples have been shown in which tritrophic indirect defenses have developed as novel interactions. For example, non‐native argentine ants are commonly attracted to extrafloral nectaries (Lach et al 2010), non‐ native maize volatiles attract both parasitoid hymenoptera and entomopathogenic nematodes (Turlings et al 1990, Rasmann et al 2005), and agricultural cotton suppresses herbivore populations with predatory mites housed in its domatia (Agrawal and Karban 1997). Unfortunately, the general importance of top–down limitation of herbivores on non‐native plants is far from clear, and much work remains in determining how much non‐native plants rely on or actively recruit natural enemies to suppress their novel herbivores (Harvey et al 2010b).…”

The hitchhiker’s guide to alien ant invasions

“…Of course, dietary requirements differ between developmental stages (larvae, adults) and caste (workers, males, queens). Diet can also differ in the same species, depending on resources, as verified by stable isotope analysis of the introduced Technomyrmex albipes (Smith, 1861) on a small island close to Mauritius: The species' diet was more carnivorous when foraging on an invasive plant, and more herbivorous when feeding on a native plant, ultimately facilitating the former (Lach et al 2010).…”