Abstract
Mutualism can facilitate the colonization, establishment, and spread of invasive species. By modifying interactions with third parties, mutualisms can have cascading community-wide effects. Both native and invasive ants are capable of forming mutualisms with hemipteran insects, preying on non-hemipteran herbivores and indirectly affecting primary production. Comparative research on the effects of both native and invasive ant exclusions on multitrophic interactions is therefore crucial for understanding the invasive potential of ants, along with any ecological consequences that invasions may have. We performed a quantitative review of the multitrophic effects of invasive and native ants on insect–plant food webs. Herbivorous insects are the most common food source for both invasive (comprising 56% of prey species caught) and native ants (55% of the prey species caught), followed by predators (31% for invasive ants, 45% for native ants). Excluding both invasive and native ants significantly reduced hemipteran abundance, and excluding invasive ants had a greater negative impact on hemipteran abundance than native ants. Native ant predation significantly reduced herbivore abundance, but excluding invasive ants had no effect. Cascading effects of native ants on plant fitness were significantly positive, but there was no significant impact of invasive ants. These findings suggest a weak relationship between the presence of invasive ants and non-hemipteran herbivore abundance. We suggest that the hemipteran–ant mutualism could represent a ‘symbiotic invasion’. The ecological dominance of invasive ants is often facilitated by hemipteran insects. This association requires invasive ant control strategies to expand beyond ants to consider mutualists.
Highlights
Biological invasion is a threat to biodiversity and leads to enormous economic and ecological costs [1,2]
We assessed the relevance of the articles based on titles and abstracts to determine their potential for meeting our selection criteria and their validity for subsequent inclusion in the meta-analysis
Because different species of ant, hemipteran insect, prey, and plant were involved in the meta-analysis, a high heterogeneity of effect size variance was expected in the analysis
Summary
Biological invasion is a threat to biodiversity and leads to enormous economic and ecological costs [1,2]. The exact outcome of these interactions is generally context dependent [19,26] Both invasive ants and native ants can form trophobiosis with hemipteran insects [27,28,29]. (b) Proposed hypotheses on cascading effects of both native and invasive ants on the local arthropod community and plant fitness. In this scenario, both native and introduced ant species perform identical roles within communities, but the magnitude of any ecological effect is more pronounced in invasive ants due to a greater intensity of mutualistic interactions. In addition to the relative magnitude of species interactions outlined by Styrsky and Eubanks [26], other factors will affect the ant-hemipteran interaction and its cascading effects on arthropods and plant fitness. This paper addressed the following two questions: (1) How do native and alien ants influence hemipteran abundance, herbivore abundance, and plant fitness? (2) Are any of these effects modified according to by climatic zone hemipteran taxon, or plant type?
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