CONICET | Buscador de Institutos y Recursos Humanos

Abstract1. It is not uncommon for one or a few species, and theirinteractions, to have disproportionate effects on other species in ecologicalcommunities. Such keystone interactions might affect how communities respond tothe invasion of non-native species by preventing or inhibiting theestablishment, spread or impact of non-native species.2. We explore whether a keystone mutualism among a hummingbird?mistletoe?marsupialpromotes ecological resistance to an invasive pollinator, the bumblebee Bombus terrestris, by comparing data collected at sites priorto bumblebee invasion to data collected 11 years after the invasion in siteswith and without the keystone mutualism.3. We built pollination networks and focused on network motifs,regarded as building blocks of networks, to identify the central pollinatorsand estimate the change in their interactions after invasion of B. terrestris. We also estimated the interaction rewiringacross the season in post-invasion networks and tested it as a possible mechanismexplaining how the keystone mutualism increased ecological resistance toinvasion.4. We found two times more species in post-invasion sites withthe keystone mutualism than in post-invasion sites without the keystonemutualism. Moreover, we found that invasive bumblebee reduced the strength andinteraction niche of the five central pollinator species while increasing itsown strength and interaction niche, suggesting a replacement of interactions.Also, we found that the keystone mutualism promoted resistance to B. terrestris invasion by reducing its negative impacts oncentral species. In the presence of the keystone mutualism, central species hadthree times more direct interactions than in sites without this keystone mutualism.The higher interaction rewiring, after invasion of B. terrestris, in sites with the keystone mutualismindicates greater chances of central pollinators to form new interactions andreduces their competence for resources with the non-native bumblebee.5. Our results demonstrate that a keystone mutualism can enhancecommunity resistance against the impacts of a non-native invasive pollinator byincreasing species diversity and promoting interaction rewiring in thecommunity. This study suggests that the conservation ofmutualisms, especially those considered keystone, could be essential forlong-term preservation of natural communities under current and future impactsof global change.

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