Impact of invasive species on the structure of plant–pollinator webs in the temperate forests of South Argentina

MORALES CAROLINA LAURA, AIZEN MARCELO ADRIÁN

Oaxaca, México

Conferencia; 1st Diversitas Open Science Conference (OSC1); 2005

Diversitas

Background and goal of study: Invasive species affect many ecosystem services, including plant pollination by animals.  The identification of key factors which influence the structure of plant–pollinator webs in communities invaded by alien species permits an assessment of the impact of biological invasions on key processes such as pollination. We asked i. whether mutualist richness varies with the origin of the mutualists, and ii. whether the plant species origin (i.e., alien or native) influences the composition of pollinator assemblages at the order and species level.   Materials and Methods: We compared mutualist richness between plants and pollinators from different origins using rarefaction curves. Using canonical correspondence analysis, we examined the structure of a plant–pollinator web comprising both alien and native plants and pollinators. We also evaluated the influence of plant origin and other potential covariates, including habitat disturbance in the composition of pollinator assemblages.   Results and discussion: Species origin did not affect mutualist richness. Alien and native plant species did not differ in the proportion of visits by insects from different orders. In spite of representing a minor fraction of total richness (3.6% of all species), alien pollinators accounted for >20% of all individuals recorded on flowers.  Thus, due to their high abundance, they could have a significant impact in terms of pollination. Plant species origin influenced the composition of pollinator assemblages at the level of species. The influence of origin persisted after accounting for other significant factors like flowering time, and habitat disturbance. This influence was determined by a preferential association between alien pollinators and alien plants. On the other hand, the main native pollinators were, on average, as closely associated with native as they were with alien plant species. Thus, alien species are well integrated into the overall community-wide pollination web; nevertheless, alien plants and pollinators may be viewed as a sub-web embedded in the overall plant–pollinator web. Conclusions: The preferential association between plants and pollinators suggests the existence of “invasive mutualisms” which may potentially favor, through pollination, a synergistic facilitation of the invasion process.