Genetic evidence for a Janzen-Connell recruitment pattern in reproductive offspring of Pinus halepensis trees.

ABSTRACT

Effective seed dispersal, combining both dispersal and postdispersal (establishment) processes, determines population dynamics and colonization ability in plants. According to the Janzen-Connell (JC) model, high mortality near the mother plant shifts the offspring establishment distribution farther away from the mother plant relative to the seed dispersal distribution. Yet, extending this prediction to the distribution of mature (reproductive) offspring remains a challenge for long-living plants. To address this challenge, we selected an isolated natural Aleppo pine (Pinus halepensis) population in Mt. Pithulim (Israel), which expanded from five ancestor trees in the beginning of the 20th century into ∼2000 trees today. Using nine microsatellite markers, we assigned parents to trees established during the early stages of population expansion. To elucidate the effect of the distance from the mother plant on postdispersal survival, we compared the effective seed dispersal kernel, based on the distribution of mother-offspring distances, with the seed dispersal kernel, based on simulations of a mechanistic wind dispersal model. We found that the mode of the effective dispersal kernel is shifted farther away than the mode of the seed dispersal kernel, reflecting increased survival with increasing distance from the mother plant. The parentage analysis demonstrated a highly skewed reproductive success and a strong directionality in effective dispersal corresponding to the wind regime. We thus provide compelling evidence that JC effects act also on offspring that become reproductive and persist as adults for many decades, a key requirement in assessing the role of postdispersal processes in shaping population and community dynamics.