ANIMAL SEED DISPERSAL INCREASES TREE MOVEMENT RATES DURING THE LATE PLEISTOCENE, BUT YOUNGER DRAYS TOO BRIEF TO CAUSE RANGE COLLAPSE (Invited Presentation)

Climate change has been implicated in all five of the great Phanerozoic mass extinction events, is thought to be responsible for a significant fraction of background extinctions, and is widely regarded as a dire threat to biodiversity in the coming centuries. Yet, despite differing extinction selectivity regimes of morphological and ecological species traits, we know relatively little about how species with different traits reacted to episodes of past climate change theorized to be causal to extinction events.

In this study, I examine the movement of plant populations in North America and Europe during the Younger Dryas (YD) as a function of their seed dispersal mechanism, using pollen data from the Neotoma database. A growing body of evidence implicates seed dispersal by animals influencing species geographic range size limits, which in turn affects their survival probabilities in all but the most intense extinction events. My recent work on seed dispersal in the Miocene of North America implies that extinction selectivity regimes on seed dispersal mechanism are different depending on the intensity of climate change experienced. The YD provides an excellent model for studying the effects of climate change intensity on species traits, having approximately the same rapidity and amplitude as projected anthropogenic warming.

I found that ranges of plant taxa are strongly affected by relict populations that persist for centuries or even millennia in habitat rendered unfavorable by climate change. Animal-dispersed taxa expand their ranges more rapidly and more consistently than taxa without animal dispersal, but the coarse taxonomic and spacial resolution provided by pollen data precludes precise estimates of the patchiness of expansions and contractions. That populations can persist in unfavorable habitat raises implications: first, the fact that a population exists does not mean that it is sustainable; second, the persistence of unsustainable populations provides conservationists with a longer time window during which human-assisted colonization (i.e. animal dispersal) can allow endangered taxa to reach more favorable habitat; third, longer-term climatic events such as glacial-interglacial cycles or the PETM may provide better analogues with which study the effects of future climate change than the YD.