MECHANISMS OF TOLERANCE TO FLORAL LARCENY IN TWO WILDFLOWER SPECIES

Tolerance of foliar damage is widely recognized as an effective defense against herbivores and pathogens. However, tolerance of the impacts of antagonists on pollination success is less well understood. Here, we extend the framework of tolerance to foliar damage to understand how plants mitigate the pollination and fitness costs of floral larceny (i.e., the consumption of floral nectar often without pollination). We focused on two mechanisms: high nectar rewards per flower to feed all floral visitors and high flower production to compensate for reproductive losses under reduced pollination and seed set. We compared the efficacy of these mechanisms in two plant species:Polemonium viscosumandIpomopsis aggregata. InPolemonium, ants acting as larcenists reduce nectar accumulation but do not completely empty flowers. When nectar reserves were augmented, ant consumption increased, negating the efficacy of this putative tolerance mechanism. Similarly, inIpomopsis, nectar addition had little effect on tolerance to larceny by bumble bees, perhaps because residual intact flowers do not have enough nectar to compensate for lost rewards. Flower production in both species mitigated some of the negative impacts of larceny on seed set. InPolemonium, flower number was not plastic in response to larceny, but large inflorescences enhanced female fitness only when larcenists were present, suggesting that “surplus” flowers in large inflorescences can function to replace reproductive losses due to larceny. InIpomopsis, high rates of larceny induced flower production, but the fecundity benefits of making more flowers declined inversely to larcenist intensity. Overall, our results suggest (1) that tolerance to floral larceny involves “banking” extra flowers to replace lost reproduction rather than maintaining pollination of ones with larceny, and (2) that the efficacy of flower production as a tolerance mechanism varies inversely to larceny rate.