Pollination and Mutualism Disruption
Pollination mutualisms are essential to the reproduction of many plants. We study the evolutionary ecology of pollination in an applied context, focused on the reproductive ecology of rare plants and the impacts of invasive species on pollinator abundance and behavior.
IMPACT OF A FLOWERING SHRUB ON POLLINATORS AND REPRODUCTIVE SUCCESS OF NATIVE PLANTS
Understanding when biological invasions will have positive, neutral, or negative effects on the pollination success of native plants remains an open and important question in ecology and conservation. Invasive plants can compete for pollinators if they attract pollinators and reduce the visitation rates of native plants, leading to lower fruit and seed production. Invasive plants can also reduce pollen quality and quantity when their pollen finds its way onto pollinators and from there onto the stigmas of native plants. This can reduce the amount of conspecific pollen and increase the likelihood of clogging stigmas with the wrong pollen. Finally, some plant species will self-fertilize when there is not sufficient outcross pollen transferred from other plants, leading to inbreeding depression. Both reductions in seed production and in offspring fitness may ultimately have negative impacts on native plant populations.
In our lab, we are using a combination of field and greenhouse studies to investigate how French broom (Genista monspessulana (L.) O.Bolós & Vigo; Fabaceae), a widespread invasive plant that produces copious and long-lived flowers, impacts the pollination of native forbs in California grasslands. We further aim to understand how underlying pollen limitation of native plants contributes to the magnitude and direction of invader impacts on native plant reproduction.
IMPACT OF AN ICONIC WETLANDS INVADER ON POLLINATOR VISITATION AT THE COMMUNITY AND SPECIES LEVELS
Through competition for pollinators, invasive plants may suppress native flora. Community-level studies provide an integrative assessment of invasion impacts and insights into factors that influence the vulnerability of different native species. With collaborator Karen Goodell at Ohio State University, we investigated the effects of the nonnative herb purple loosestrife (Lythrum salicaria L.; Lythraceae) on pollination of native species in 14 fens of the eastern United States. We compared visitors per flower for 122 native plant species in invaded and uninvaded fens and incorporated a landscape-scale experiment, removing L. salicaria flowers from three of the invaded fens. Total flower densities were more than three times higher in invaded than uninvaded or removal sites when L. salicaria was blooming.
Despite an increase in the number of visitors with the number of flowers per area, visitors per native flower declined with increasing numbers of flowers. Therefore, L. salicaria invasion depressed visitation to native flowers. In removal sites, visitation to native flowers was similar to uninvaded sites, confirming the observational results and also suggesting that invasion had not generated a persistent build-up of visitor populations. To study species-level impacts, we examined effects of invasion on visitors per flower for the 36 plant species flowering in both invaded and uninvaded fens. On average, the effect of invasion represented about a 20% reduction in visits per flower. We measured the influence of plant traits on vulnerability to L. salicaria invasion using meta-analysis. Bilaterally symmetrical flowers experienced stronger impacts on visitation, and similarity in flower color to L. salicaria weakly intensified competition with the invader for visitors.
Finally, we assessed the reproductive consequences of competition with the invader in a dominant flowering shrub, Dasiphora fruticosa (L.) Rydb (Rosaceae). Despite the negative effect of invasion on pollinator visitation in this species, pollen limitation of seed production was not stronger in invaded than in uninvaded sites, suggesting little impact of competition for pollinators on its population demography. Negative effects on pollination of native plants by this copiously flowering invader appeared to be mediated by increases in total flower density that were not matched by increases in pollinator density. The strength of impact was modulated across native species by their floral traits and reproductive ecology.
For more details, see:
Goodell, K., & Parker, I. M. 2017. Invasion of a dominant floral resource: effects on the floral community and pollination of native plants. Ecology, 98(1), 57-69.
You can find publications from these projects and more at Ingrid's Google Scholar page.