Preferential nectar robbing of flowers with long corollas: experimental studies of two hummingbird species visiting three plant species

Abstract

Long flower tubes have been traditionally viewed as the result of coevolution between plants and specialized, legitimate, long billed-pollinators. However, nectar robbers may have played a role in selection acting on corolla length. This study evaluated whether hummingbirds are more likely to rob flowers with longer corollas from which they cannot efficiently extract nectar with legitimate visits. We compared two hummingbird species with similar bill lengths (Lampornis amethystinus and Colibri thalassinus) visiting floral arrays of artificial flowers with exaggerated corolla lengths, and also evaluated how the birds extract nectar rewards from medium to long corollas of three hummingbird-pollinated plants (Salvia mexicana, S. iodantha and Ipomoea hederifolia). The consequences of foraging for plant fitness were evaluated in terms of seed production per flower. Variation in seed production after legitimate visits of hummingbird-pollinated plants was mostly explained by differences in pollinator effectiveness. Seed production did not increase with the number of legitimate visits to a flower, except in I. hederifolia. We found that birds were more likely to rob both artificial and natural flowers with long corolla tubes. Nectar robbing was not observed on short-corolla flowers of Salvia spp., but robbing negatively affected seed production of long-tubed flowers of I. hederifolia. Significant differences between hummingbird species in the use of this behavior were observed, but males and females behaved alike. We suggest that short-billed hummingbirds with enlarged bill serrations (the edge of both tomia finely toothed) may have an advantage in illegitimately feeding at long-corolla flowers. This raises the possibility of counter-selection on increasing corolla length by nectar robbers.

Feeding behavior of hummingbirds and perching birds on Erythrina speciosa Andrews (Fabaceae) flowers in an urban area, Londrina, Paraná, Brazil

“…Such birds have bills that are wider and shorter than those of hummingbirds, which probably preclude them to access the nectar of E. speciosa in a way other than perforating the flower (INOUYE 1983). The distinction between nectar thieves and robbers is important because the latter may have a greater effect in reducing the reproductive potential of the plant by damaging sexual tissues and often destroying or removing the entire flower (NEILL 1987, TRAVESET et al 1998, LARA & ORNELAS 2001, RAGUSA-NETTO 2002. Nectar robbing by T. sayaca often did cause reproductive tissue damage.…”

Pollinators and nectar robbers cause directional selection for large spur circle in Impatiens oxyanthera (Balsaminaceae)

“…3). Previous studies had found that conflicting selection pressures were imposed by pollinators and antagonists on the same traits (Brody 1992;Lara and Ornelas 2001;Galen and Cuba 2001;Gómez 2003;Strauss and Irwin 2004;Navarro and Medel 2009). Nectar robbers shifted selection direction to balance selection on floral traits by pollinators (Lara and Ornelas 2001;Young 2008).…”

“…Studies on ecological and evolutionary consequences of species interactions have been mainly focusing on single pairwise effects, such as pollinator-mediated (Campbell et al 1996;Alexandersson and Johnson 2002;Sandring and Å gren 2009;Cuartas-Domínguez and Medel 2010; or nectar robber-mediated (Lara and Ornelas 2001;Urcelay et al 2006;Castro et al 2008;Young 2008;Navarro and Medel 2009) selection on floral traits. However, single pairwise interaction seldomly exists in isolation and can be interfered by other community members (Gómez 2003;Cariveau et al 2004;Lavergne et al 2005;Brody et al 2008;Sánchez-Lafuente 2007;Bartkowska and Johnston 2012).…”

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

“…Tightly packed flowers may physically deny nectar robbers access to nectar spurs or the sides of corolla tubes (Proctor et al 1996). Short corolla tubes may decrease the frequency of robbing by some hummingbirds (Lara and Ornelas 2001). Bract liquid that can create a ''moat'' around flowers may prevent nectar-robbing ants from gaining access to nectar (Wootton and Sun 1989).…”

“…Nectar robbers can reduce plant fitness to degrees comparable to, or even surpassing, fitness reduction by herbivores Bergelson 1997, Irwin andBrody 2000). Damage to floral tissue can have stronger links to plant fitness than does damage to leaf tissue (reviewed in Strauss et al 2003); nectar robbing can reduce female fitness by 50% (e.g., Brody 2000, Lara andOrnelas 2001) and estimates of male fitness by up to 80% (Irwin and Brody 1999). Yet, the mechanisms by which plants resist nectar robbers are less well known than mechanisms associated with resistance to herbivores.…”