Limited evidence for a consistent seed mass‐dispersal trade‐off in wind‐dispersed pines

Abstract

Abstract Much of the variation in dispersal potential among seeds of different plant species has been related to a putative trade‐off between dispersal potential and seed mass. Yet to date there are few taxonomically controlled comparisons that explore the generality of this relationship across and within multiple species. We measured the seed mass and dispersal traits across multiple pine species that encompassed a 100‐fold range in seed mass. We expected that for the larger seeded species, the resource investment required in the cone to house seeds and their wings may constrain dispersal potential. We examined the relative roles of samara and cone traits in determining the terminal velocity, and investigated how the relative investment of resources in cone structure related to seed mass and samara dispersal traits. Finally, we examined the partitioning of variation in seed mass and terminal velocity within and among individuals of each species. We found a strong positive relationship between seed mass and samara terminal velocity across all 12 species; however, this seed mass‐dispersal trade‐off was only significant within two of our species. For most species, wing loading was the most important trait determining samara terminal velocity. Across species, increases in cone investment were associated with heavier seeds with longer wings but higher terminal velocities, while within‐species increases in cone investment were associated with decreases in terminal velocity. The majority of the variation in terminal velocity occurred within individual trees, while seed mass variation mostly occurred among trees and may therefore be subject to stronger selection pressure. Synthesis. We have found strong support for a trade‐off between seed mass and dispersal potential across a wide range of wind‐dispersed Pinus species. Importantly, we show that this trade‐off is largely absent within species, potentially reducing selective pressure. This may be largely due to the relationships between cone investment and samara traits, whereby increases in cone investment result in a proportionally greater increase in wing size than seed mass. Where resources are limited, investment in seed mass may be prioritized over dispersal.