Competition–colonisation trade‐offs are found among but not within wind‐dispersed Pinus species

Abstract

1. The competition– colonisation trade- off is recognised as a key mechanism for diversity maintenance, whereby weak competitors can avoid competition with stronger competitors due to their greater dispersal ability. To date, most theoretical and empirical work has focused on trade- offs among different species yet a within- species perspective is crucial to assess the scope for natural selection on competition– colonisation trade- offs. 2. For six wind- dispersed Pinus species encompassing a wide range of seed masses, we examined whether within and among species there was evidence that heavier seeds typically disperse shorter distances but produce seedlings that are stronger competitors with a higher likelihood of successful establishment, under different treatment conditions. 3. Within species, we found seedling establishment to be independent of diaspore terminal velocity (a measure of dispersal potential), which would maximise the variation in potential dispersal distances and locations reached by the seeds shed from a parent tree, and therefore the chances that some offspring will reach a favourable recruitment site. However, among Pinus species the likelihood of seedling emergence and survival was higher in species that produce heavier seeds with higher terminal velocity. 4. We found a marked competition– colonisation trade- off among all six species consistent with expectations from coexistence theory. In contrast, within species, there was no evidence of competition– colonisation trade- offs for any species, despite differences in the relationships between diaspore mass and terminal velocity. This is consistent with weak selection within species for a competition– colonisation trade- off. The results suggest that within- species trade- offs do not influence the risk of invasive spread.