Holocene variability of an Amazonian hyperdominant

Little is known regarding the long-term stability or instability of Amazonian plant communities. We assessed whether the most abundant species, hyperdominants, may have risen to prominence at the Pleistocene-Holocene transition, following subsequent changes in moisture regimes, or as a result of human activity later in the Holocene. The fossil pollen history of the commonest western Amazonian tree, Iriartea deltoidea (hereafter Iriartea), is investigated using fossil pollen data from 13 lakes. Iriartea is a monospecific genus with diagnostic pollen. It is also considered a useful' plant, and its abundance could have been enriched by human action.Iriartea pollen was found to have increased in abundance in the last 3000years, but did not show a consistent relationship with human activity. The suggestion that the hyperdominants in modern Amazonian forests are a legacy of pre-Columbian people is unsupported. The abundance of Iriartea pollen is related to increasing precipitation, not human activity over the last 3000years. This member of the hyperdominant category of Amazonian trees has only recently acquired this status.Synthesis. Our findings are consistent with the observation that communities in complex systems are ephemeral. The populations of even the most abundant species can change over a few tens of generations. The relative abundance of tree species, even in relatively stable systems such as those of Amazonian floodplains, changes on ecological not evolutionary timescales.