Effects of wildfire on floral display size and pollinator community reduce outcrossing rate in a plant with a mixed mating system

• Published in: American journal of botany Vol. 105; no. 7; pp. 1154 - 1164
• Main Authors: LoPresti, Eric F., Van Wyk, Jennifer I., Mola, John M., Toll, Katherine, Miller, Timothy J., Williams, Neal M.
• Format: Journal Article
• Language: English
• Published: United States John Wiley and Sons, Inc 01.07.2018; Botanical Society of America, Inc
• Subjects: autogamy; Bee assemblages; Bees; Chaparral; Climate change; Communities; Demography; disturbance; Flowers; Flowers & plants; Forest & brush fires; geitonogamy; Lamiaceae; McLaughlin Reserve; Morphology; Mutualism; mutualisms; Plant reproduction; pollen transfer; Pollination; Pollinators; Polymorphism; Populations; RESEARCH ARTICLE; wildfire; Wildfires; disturbance; geitonogamy; mutualisms; pollen transfer; McLaughlin Reserve; wildfire; Lamiaceae; autogamy; Bee assemblages
• ISSN: 0002-9122; 1537-2197
• DOI: 10.1002/ajb2.1129

Premise of the Study Wildfire changes the demography, morphology, and behavior of plants, and may alter the pollinator community. Such trait changes may drastically alter the outcome of pollination mutualisms on plants; however, the direct role of fire on these mutualisms is poorly known. Methods Following a pair of fires in the northern California coast range chaparral, we censused floral visitor communities of Trichostema laxum (Lamiaceae), quantified visiting bee behavior, and estimated outcrossing rates using a widespread Mendelian recessive floral polymorphism across a matrix of populations in burned and unburned sites. We also compared pre‐ and postfire floral visitation in two populations. Results Outcrossing rates were significantly lower in burned areas; however, our data suggest that the much larger size of plants in burned areas, not burn status itself, drove this pattern. Large‐bodied bees dominated floral visitor communities after fire, likely recruiting to the abundant postfire floral resources. These bees visited more flowers per plant than did the smaller bees prevalent before fire and in unburned areas, likely increasing selfing through geitonogamy (within‐plant pollination), an effect made possible by the far larger size of plants in burned areas. Conclusions Outcrossing rates dropped substantially after wildfires because of changes in the pollinators, plant display size, and their interactions. Reductions in outcrossing following fire may have important implications for population resilience and evolution in a changing climate with more frequent fires.