DOES SEED DISPERSAL AFFECT RATE OF SPREAD DURING PLEISTOCENE CLIMATE CHANGE?

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 as a function of their seed dispersal mechanism, using pollen data from the Neotoma database. A growing body of evidence implicates seed dispersal as 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 Younger Dryas provides an excellent model for studying the effects of climate change intensity on species traits, because the Younger Dryas was far more intense in Europe (2-6 degrees C) than elsewhere in the world (1-2 degrees C).

Preliminary results suggest that ranges of plant taxa are strongly affected by relict populations that can persist for centuries in habitat rendered unfavorable by intense climate change before eventual extirpation. Animal-dispersed taxa expand their ranges more rapidly than taxa without animal dispersal, but extremophiles are more effective at persisting in the face of long-term climate change, especially in coastal habitats where climate is moderated by maritime influence. That populations can persist for centuries in unfavorable habitat raises implications for conservation: first, the fact that a population exists does not mean that it is sustainable, and second, the presence of these persisting 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.