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Pre-Dispersal Biology of Pistacia lentiscus (Anacardiaceae): Cumulative Effects on Seed Removal by Birds

Pedro Jordano
Oikos
Vol. 55, No. 3 (Jul., 1989), pp. 375-386
Published by: Wiley on behalf of Nordic Society Oikos
DOI: 10.2307/3565598
Stable URL: http://www.jstor.org/stable/3565598
Page Count: 12
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Pre-Dispersal Biology of Pistacia lentiscus (Anacardiaceae): Cumulative Effects on Seed Removal by Birds
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Abstract

This paper examines within-population variation in realized fecundity of Pistacia lentiscus (Anacardiaceae) and considers how plant traits relevant to the interaction with avian seed dispersers do influence it. A highly variable fraction of final-sized fruits (on average, 80.1% and 55.5% in two consecutive study years) contained empty seeds, either because of embryo abortion or parthenocarpy, but these fruits were retained and eventually consumed by birds. A total of 26 bird species consumed the fruits, with 19 of them being seed dispersers accounting for the removal of 82.5% and 83.3% of the final-sized fruit crop in two study years. Only four bird species removed 82.2% of the seeds and pulp/seed predators took 6.0%. Plant characteristics directly related to fecundity had strong effects on estimates of dispersal success relevant to fitness, accounting for 82.4% of its variance when holding constant the effects of fruit-design traits; the latter accounted for 1.8% of this variance. Fruit removal by frugivores had a negligible contribution to variation in realized reproductive output. This was largely attributable to the cumulative effects of the pre-dispersal phase, when great losses of potential fecundity occurred as abortion of embryos or production of parthenocarpic fruit. Variation in removal rates by frugivores did not "screen-off" these pre-dispersal effects.

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