Floral Resource Sharing by Bumblebees and Hummingbirds in Pedicularis (Scrophulariaceae) Pollination

Abstract

MACIOR, L. W. (Dept. Biol., Univ. Akron, Akron, OH 44325) Floral resource sharing by bumblebees and hummingbirds in Pedicularis (Scrophulariaceae) pollination. Bull. Torrey Bot. Club 113:101-109. 1986.-Pedicularis densiflora in California was found to be animal pollinator dependent. Younger flowers with short corolla tubes were pollinated by short-tongued Bombus edwardsii workers foraging primarily for nectar, while older flowers with deep tubes were pollinated by nectar-foraging Anna and rufous hummingbirds. Scarlet corollas apparently attract birds, while magenta calyces and floral bracts with highly ultraviolet reflective hairs attract bumblebees. Nectar concentration (sucrose equivalents) varied from 15.0 to 24.5%; only fructose and sucrose were present. Cinematographic and stereophotographic records indicated that the flowers are pollinated only nototribically by birds and insects. Of 83 corbicular pollen loads from 193 B. edwardsii worker pollinators, 55% contained P. densiflora pollen, and 60% contained pollen of Dodecatheon hendersonii, suggesting that these two plants share pollinators by synchronously supplying complementary resources in the same plant community. The earlier blooming Arctostaphylos did not effectively deflect Bombus pollinators from P. densifora, but observations on a community including synchronously blooming Arctostaphylos and Pd. aurantiaca, a subspecies with variably colored flowers, indicated that Arctostaphylos preferentially attracted Bombus pollinators with hummingbirds exclusively pollinating Pd. aurantiaca. Pedicularis densiflora is considered a species in transition between two pollination syndromes, influenced by the biotic and physical circumstances of the environment.