The effect of seed-dispersal timing on seedling recruitment is modulated by environmental conditions that vary across altitude in a threatened palm.

BACKGROUND AND AIMS

The timing of seed dispersal determines the environmental conditions that plants face during early life stages. In seasonal environments, selection is expected to favour dispersal timing that is matched to environmental conditions suitable for successful recruitment. Our aim here was to test whether the timing of seed dispersal influences seedling establishment success in two populations of Euterpe edulis that are located at contrasting altitudes, have different seed-dispersal phenologies and are subjected to distinct climatic conditions.

METHODS

We sowed E. edulis seeds in contrasting altitudes on different dates, and monitored seed germination, emergence and seedling establishment at each altitude over 4 years. At the high-altitude site, five seed-dispersal cohorts were established during the natural dispersal period. At the low-altitude site, three seed-dispersal cohorts were established during natural dispersal, and two were established either before or after natural dispersal.

KEY RESULTS

At the high-altitude site, seed-dispersal timing did not affect seed germination, seedling emergence or seedling establishment success. In contrast, at the low-altitude site, late seed dispersal near the end of the wet season resulted in a lower probability of seedling establishment, possibly due to the exposure of seeds, germinants and seedlings to unfavourable drought conditions. In addition, at the low-altitude site, the natural seed-dispersal period was poorly matched to favourable environmental conditions for seedling establishment.

CONCLUSIONS

The greater effect of seed-dispersal timing on seedling establishment at the low-altitude site is probably related to a more seasonal and drought-prone environment that favours a restricted period of seed dispersal. The magnitude of the effect of dispersal timing on seedling establishment success was modulated by environmental conditions that vary across altitude. Furthermore, reproductive phenology appears to be subject to more intense selection at the lower limit of the altitudinal range, due to a more restrictive window of opportunity for successful seedling establishment.