In 1899, botanist Clement Reid identified an apparent anomaly in post-glacial vegetation history: the documented northward expansion of heavy-seeded deciduous trees across Europe following the Last Glacial Maximum occurred far more rapidly than could be explained by observed dispersal mechanisms, such as local wind distribution and standard animal foraging. If these species had been confined entirely to southern Mediterranean refugia during the glacial peak, their migration to northern Europe would have required tens of thousands of years longer than the fossil pollen record reveals. To resolve "Reid's paradox," paleoecologists hypothesized both rare long-distance dispersal events by corvid birds and the existence of cryptic northern microrefugia—small, climatically buffered valleys where isolated tree populations persisted at higher latitudes. While conventional macrofossil evidence for such northern populations was long elusive, recent analyses of sedimentary ancient DNA preserved in lake beds have confirmed the presence of localized tree stands well north of the Mediterranean belt during the height of the glaciation. Consequently, the actual distances that recolonizing forests had to traverse were significantly shorter than traditional biogeographical models assumed, easing the theoretical burden placed on extreme seed-dispersal mechanisms.
Based on the passage, which of the following assertions are logically supported? (Select all that apply.)
- Traditional biogeographical models of post-glacial forest recolonization overestimated the geographical distance that certain deciduous tree populations needed to traverse after the Last Glacial Maximum.Answer
- BSedimentary ancient DNA has replaced fossil pollen records as the primary empirical standard for establishing the overall timeline of post-glacial plant migration.
- The absence of identifiable macrofossil remains in a region does not establish conclusively that tree populations were entirely absent from that area during a glacial period.Answer
- DCorvid birds were responsible for a larger total volume of post-glacial seed dispersal in Europe than any other animal group.
- EThe rapid expansion of deciduous trees proved that local wind dispersal operates more rapidly across glaciated terrain than across densely forested landscapes.