Testing hypotheses for excess flower production and low fruit-to-flower ratios in a pollinating seed-consuming mutualism

Oikos
By: , and 

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Abstract

Pollinator attraction, pollen limitation, resource limitation, pollen donation and selective fruit abortion have all been proposed as processes explaining why hermaphroditic plants commonly produce many more flowers than mature fruit. We conducted a series of experiments in Arizona to investigate low fruit-to-flower ratios in senita cacti, which rely exclusively on pollinating seed-consumers. Selective abortion of fruit based on seed predators is of particular interest in this case because plants relying on pollinating seed-consumers are predicted to have such a mechanism to minimize seed loss. Pollinator attraction and pollen dispersal increased with flower number, but fruit set did not, refuting the hypothesis that excess flowers increase fruit set by attracting more pollinators. Fruit set of natural- and hand-pollinated flowers were not different, supporting the resource, rather than pollen, limitation hypothesis. Senita did abort fruit, but not selectively based on pollen quantity, pollen donors, or seed predators. Collectively, these results are consistent with sex allocation theory in that resource allocation to excess flower production can increase pollen dispersal and the male fitness function of flowers, but consequently results in reduced resources available for fruit set. Inconsistent with sex allocation theory, however, fruit production and the female fitness function of flowers may actually increase with flower production. This is because excess flower production lowers pollinator-to-flower ratios and results in fruit abortion, both of which limit the abundance and hence oviposition rates, of pre-dispersal seed predators.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Testing hypotheses for excess flower production and low fruit-to-flower ratios in a pollinating seed-consuming mutualism
Series title Oikos
DOI 10.1111/j.0030-1299.2004.13058.x
Volume 105
Issue 3
Year Published 2004
Language English
Publisher Wiley
Contributing office(s) Southeast Ecological Science Center
Description 8 p.
First page 633
Last page 640
Country United States
State Arizona
Other Geospatial Organ Pipe Cactus National Monument
Online Only (Y/N) N
Additional Online Files (Y/N) N