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Nonflying Mammal Pollination of Southern African Proteas: A Non-Coevolved System

Delbert Wiens, John P. Rourke, Brenda B. Casper, Eric A. Rickart, Timothy R. LaPine, C. Jeanne Peterson and Alan Channing
Annals of the Missouri Botanical Garden
Vol. 70, No. 1 (1983), pp. 1-31
DOI: 10.2307/2399006
Stable URL: http://www.jstor.org/stable/2399006
Page Count: 31
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Nonflying Mammal Pollination of Southern African Proteas: A Non-Coevolved System
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Abstract

Traits characterizing those proteas adapted for pollination by nonflying mammals include: bowl-shaped heads bearing fleshy bracts, these borne on short, flexible peduncles, often at or near ground level (geoflorous) and hidden beneath dense overlying foliage (cryptic), and producing copious nectar (ca. 1.8 ml/head, standing crop); individual florets with wiry, yet flexible styles and a nectar-stigma distance of 10 mm; a distinctive yeastlike odor; nocturnal anthesis; sucrose-rich nectar with a high total carbohydrate content (ca. 36%) and a relatively low proportion of amino acids. Evidence of small-mammal visitation to protea flowering heads includes: the presence of pollen on the rostra (carried in a position to effect pollination when foraging for nectar); the transport of fluorescing powders to flowering heads both within and between plants; the accumulation of small-mammal feces in flowering heads, and the destruction of exclosure bags containing nectar-rich heads. The period of greatest small-mammal activity (1800 hr.) coincides with maximum flower opening. T maze experiments showed that small mammals, when given a choice between typically bird-pollinated proteas and those having characteristics of flowers pollinated by nonflying mammals, always foraged on the latter. That small mammals can effect pollination is indicated by their foraging behavior on flowering heads while in captivity, the morphological "fit" between individual florets and the rostra of small mammals, and by selective exclosure experiments that reduced seed set (50% and 95%) when small mammals were excluded and visitation was limited to insects (mostly honey bees). The nectar produced by these proteas meets the energy requirements of the small-mammal community for only several days annually, thus coevolution is impossible. Proteas adapted for pollination by nonflying mammals have evolved unilaterally, probably from bird-pollinated prototypes, possibly in response to progressive decrease in population size. Recent discoveries in the Neotropics of flowers with some similar characteristics and also pollinated by nonflying mammals support the existence of a worldwide class of flowers adapted for such pollinators.

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