Disruption of ant-seed dispersal mutualisms by the invasive Asian needle ant (Pachycondyla chinensis)

Abstract

By disrupting the structure of native ant assemblages, invasive ants can have effects across trophic levels. Most studies to date, however, have focused on the impacts just two species (Linepithema humile and Solenopsis invicta). The impacts of many other invasive ant species on ecological processes in their introduced range are unknown. In this study we tested the hypothesis that the invasive ant Pachycondyla chinensis disrupts ant-seed dispersal mutualisms by displacing native ant species, especially the keystone mutualist Aphaenogaster rudis, while failing to disperse seeds itself. In a paired design we measured the impact of P. chinensis on the native ant-plant seed dispersal mutualism. The number of A. rudis workers was 96% lower in invaded than in intact plots, and the number of seeds removed was 70% lower in these plots. Finally, in invaded plots the abundance of Hexastylis arifolia, a locally abundant myrmecochorous plant, was 50% lower than in plots where P. chinensis was absent. A parsimonious interpretation of our results is that P. chinensis causes precipitous declines in the abundance of A. rudis within invaded communities, thereby disrupting the ant-plant seed dispersal mutualisms and reducing abundances of ant-dispersed plants. In sum, the magnitude of the effects of P. chinensis on seed dispersal is quantitatively similar to that documented for the intensively studied invasive Argentine ant. We suggest that more studies on the impacts of lessstudied invasive ant species on seed dispersal mutualisms may increase our knowledge of the effects of these invaders on ecosystem function.

The unnoticed effect of a top predator on complex mutualistic ecological interactions

“…Disruptions of mutualistic systems (pollination and seed dispersal) have often been documented, but their ecological implications have remained less extensively studied (Traveset and Richardson 2006;Rodríguez-Cabal et al 2011;Markl et al 2012;Traveset et al 2012). For example, mutualistic disruptions can induce cascading effects on biodiversity, but they remain quite unknown in an ecological context (Aslan et al 2013), especially on islands.…”

Non-native and native organisms moving into high elevation and high latitude ecosystems in an era of climate change: new challenges for ecology and conservation

“…Warren and Chick (2013) showed how changing climates influenced the distribution of native ant species along an elevation gradient in southern United States, with consequences for seed dispersal mutualisms. In addition, several studies in low elevation forest sites have demonstrated how the Asian needle ant (Brachyponera chinensis) alters native ant communities and seed-dispersal mutualisms (e.g., Rodriguez-Cabal et al 2012) and models suggest that this invasive ant is likely to move upward in both latitude and elevation (Bertelsmeier et al 2013). …”

Mutualism between co-introduced species facilitates invasion and alters plant community structure

“…In this context, our mesocosm approach is unique; most previous research has compared seed removal between invaded and uninvaded sites (e.g. [6,43]). Results in these previous studies may be confounded by pre-existing differences between invaded and uninvaded sites or a higher overall density of ants in invaded sites [34,36].…”