The Dual Role of Floral Traits: Pollinator Attraction and Plant Defense

Abstract

Abstract. Plants are under siege from a diversity of enemies that consume both leaf and floral parts. Plants resist damage to leaves in a variety of ways, and we now have a rich literature documenting how plants defend themselves against herbivore attack. In contrast, the mechanisms by which plants resist enemies that consume floral parts or resources are much less known, even though damage to floral tissue usually has tighter links to plant fitness than damage to leaf tissue. Many plants experience nectar robbing, whereby floral visitors remove nectar from flowers, often without pollinating. Nectar robbers can reduce plant fitness to degrees comparable to, or even surpassing, reduction by herbivores. However, because nectar attracts both pollinators and nectar robbers, plants face a dilemma in defending against nectar robbers without also deterring pollinators. Here, we extend the conceptual framework of resistance to herbivores to include resistance to nectar robbers, focusing on nectar traits. We review published data and find that an array of nectar traits may deter robbers without deterring pollinators. Although resistance traits against robbers have been broadly identified, the costs and benefits of these traits in terms of plant fitness remain poorly understood. We present data showing that a nectar trait (dilute nectar) might directly, as well as indirectly, benefit plant fitness by deterring nectar-robbing bumble bees of Ipomopsis aggregata without deterring hummingbird pollinators. However, the magnitude of any plant fitness benefit will depend on the degree to which plants are pollen-vs. resource-limited in a given year. The results of our work offer both conceptual and empirical insight into how plants cope with attack by nonpollinating floral visitors through a relatively unexplored trait, nectar.

How plant?animal interactions signal new insights in communication

“…Likewise, bumblebees Bombus spp. pollinate some flowers but rob nectar from hummingbird-pollinated flowers [31].…”

Floral Scent Contributes to Interaction Specificity in Coevolving Plants and Their Insect Pollinators

“…The production of such a diverse array of compounds is likely to incur energetic (Gershenzon 1994;Wright and Schiestl 2009) and ecological costs, because the same compounds that attract mutualistic insects also may attract antagonistic herbivores and seed predators (Irwin et al 2004;Proffit et al 2007;Schiestl et al 2011;Theis 2006;Theis and Adler 2012;Wright and Schiestl 2009).…”

Geographic patterns in fruit colour diversity: do leaves constrain the colour of fleshy fruits?

“…Alternatively, it is well known that the synthesis of plant pigments in vegetative tissue may vary according to abiotic factors such as temperature (Hoch et al 2003;Schaefer and Wilkinson 2004). Similarly, fruit and flower colours may vary with soil (Traveset and Willson 1998;Schemske and Bierzychudek 2007) or be influenced greatly by selection of flower and fruit predators (Irwin et al 2004;Whitney and Stanton 2004). Therefore, both fruit and background colours could vary geographically according to abiotic factors, independently of selection from dispersers.…”