Seasonality of Fruit Characters and Seed Removal by Birds

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Abstract
I examined the fruit characters of 21 species of plants fruiting from July to September in the Rainbow Creek Research Natural Area in SE Washington, USA, in order to examine the hypotheses on fleshy-fruited and frugivory derived from earlier studies in temperate deciduous and tropical forests. Mean seed mass increased from summer to autumn, but other morphological and chemical factors that may mediate levels of frugivory did not change consistently. Frugivores removed larger fruits of Clintonia uniflora sooner than smaller fruits in 1981, but not in 1982. Among arrays of five fruits presented to birds in 1983, Disporum hookeri was removed significantly faster than Rosa gymnocarpa in one trial; D. hookeri, D. tachycarpum, and Symphoricarpos albus were removed significantly faster than R. gymnocarpa in a second trial, in which I used the same five species of fruits. Percentage removal among five species correlated best with amount of pulp per fruit, less well with fruit diameter and percentage lipid, and was independent of protein, minerals, pulp to seed ratio, and size of seeds in the fruit. Seasonal trends in fruit characters in conifer forests differed from increases in protein, lipid, and potassium reported for fruits of deciduous forests of North America and Europe.