Biogeography of the ‘Lost World’: a palaeoecological perspective

The uniqueness of the flora from the remote tableaux summits of the Guayana region has been explained either as the result of a long history of evolution in isolation (Lost World hypothesis or LW) or by alternating upward and downward displacements during the glacial–interglacial Quaternary cycles (Vertical Displacement hypothesis or VD). So far, the problem has been addressed solely on the basis of present-day floristic observations. This paper faces the problem from a Quaternary palaeoecology perspective using recent palynological findings in the area, comparisons with palaeoecological records from Neotropical mountains and lowlands of similar latitude, isotopic glacial–interglacial records from marine and ice cores, and different points of view about the response of organisms to Quaternary climatic changes, with emphasis on the LGM and the debate on the existence or not of Neotropical refugia. It is concluded that both LW and VD hypotheses, together with autoecological and synecological considerations, are needed to explain the present-day specialisation and endemism of the flora from the tableaux summits. The case of a highly endemic genus (Chimantaea, Asteraceae) is analysed as an example, to illustrate the usefulness and limitations of the different arguments to account for its biogeographical pattern. Some ideas are provided for future research, including a more extensive sampling strategy, the use of molecular phylogenetics, the evaluation of the individualistic versus the community approach, and the use of island biogeography and metapopulation methods on present-day floristic data.