Comparative study of the reproductive ecology of two co-occurring related plant species: the invasive Senecio inaequidens and the native Jacobaea vulgaris

Abstract

Background and aims – A previous study showed that the visitation rate by pollinators and the seed set of the exotic invasive Senecio inaequidens (Asteraceae) were higher compared to the native relative, Jacobaea vulgaris. The first aim of the present study was to assess if these results could be explained by differences in self-fertility, nectar rewards or floral display between the two species. Moreover, in a second step, we examined if the higher visitation rate on S. inaequidens has a negative effect on the reproductive success of J. vulgaris. Methods – Self-fertility was estimated after self- and cross-hand pollinations. Nectar volume, total sugar concentration and sugar composition were analysed on plants cultivated under controlled conditions. In the field, in order to assess the effect of floral display and impact of the invasive on the pollination success of the native, insect behaviour was assessed by comparing visitation rates, number of visitors per 10 min observation and individual censuses. Floral display (density of capitula per unit area) was artificially modified by clipping or grouping inflorescences in both species.Key results – In terms of self-fertility, seed sets were similarly low after self-pollination (11–12%) for both species. S. inaequidens produced lower amounts of nectar with lower sugar concentration compared to J. vulgaris. No influence of floral display was detected on insect visitation rates. The presence of S. inaequidens did not alter pollinator visits and seed set of J. vulgaris. Conclusions – Other traits need to be investigated to explain the different visitation rates and reproductive success between the two species. The higher seed set of S. inaequidens could be due to a higher outcrossing rate, or more frequent pollinator movements between individuals.