INTERPOPULATIONAL VARIATION IN FRUIT PRODUCTION: THE ROLE OF POLLINATION‐LIMITATION IN THE OLYMPIC MOUNTAINS

Abstract

Fruit set varied from a mean of 44% to 93% among six populations of Veronica cusickii L. (Scrophulariaceae) spanning a distance of 13 km in the Olympic Mountains, WA. Hand pollinations in three populations showed that this variation resulted primarily from differences in the level of limitation by insect pollination. In every pollination, hand‐pollinated flowers averaged at least 82% fruit set. In 1981 and 1982, addition of excess pollen significantly increased mean fruit set per plant in the Blue Mountain population, but not in two other populations with higher natural fruit sets. At Blue Mountain, hand pollination more than doubled the mean seed set of V. cusickii and also significantly increased seed set in two of three other species visited primarily by flies or solitary bees. Pollination‐limitation appears to be common at this site where the weather is frequently cold and damp.