Plant-pollinator interactions in sympatric exotic and native Senecio species: is facilitation or competition for pollinators occurring?
Eve M. WhiteA,B, John C. WilsonA and Anthony R. ClarkeA
A School of Natural Resource Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia.
B Current address: Alan Fletcher Research Station, Department of Natural Resources and Water and CRC for Australian Weed Management, PO Box 36, Sherwood, Queensland 4075, Australia.
The role of indirect interactions in invasion biology has rarely been addressed. Indirect interactions between two plant species may be mediated by shared pollinators: the presence of one plant species can have either a negative impact on pollination (and seed set) in another by competing for pollinators, or a positive effect by facilitating pollinator visitation. We investigated whether facilitation or competition for pollination was occurring between the closely related native Senecio pinnatifolius (A.Rich) and exotic S. madagascariensis (Poiret) in south-east Queensland. Visitation rates by honeybees and syrphid species, as well as seed set in each Senecio species, were assessed in naturally occurring mixed and pure stands. The exotic S. madagascariensis did not affect visitation rates to the native, but seed set of the native species was higher in mixed populations. The presence of native S. pinnatifolius caused a reduction in honeybee visits and an increase in syrphid visits to the exotic plant, but altered visitation patterns were not reflected in a change in seed set in the exotic.
Keywords: fireweed, indirect effects, invasive species, plant-pollinator interactions,visitation rates.
Plant Protection Quarterly (2008) 23 (3) 120-126.