PROBABILITY OF SPECIATION FOLLOWING VAST, LATE MIOCENE VOLCANIC INTERRUPTIONS IN THE PACIFIC NORTHWEST

The impact of large-scale volcanic eruptions on landscapes can affect many processes ranging from interrupting or redirecting regional hydrological systems and soil processes to generating temporary changes in global climate. Though studies exist, less is known of the impact of large-scale volcanic eruptions on ecosystems and extinction, while even less is known of their impact on speciation. In deposits throughout the Pacific Northwest a special combination and association of volcanic magnitude with palaeoecological yield frequently presents unique prospects for inquiry. As an example of the scale and impact of these eruptions, the 7 Ma Rattlesnake Tuff (RST)—a high temperature ash flow (~860°C pre-eruptive temperature)—was likely 1) deposited in no more than days and 2) covered an area greater than 40,000 km². By comparison, the ecological unit for the migrating herds of the Serengeti—a roughly flat, west-sloping plateau—is approximately 25,500 km². With this in mind it is unproblematic to imagine how whole populations and communities of the past could be cancelled with unharmed neighboring communities divided by distances too great to traverse with no access to forage and barricaded by nearby mountain ranges.

In this study particular attention is given to large ash flow tuffs of central and eastern Oregon, the RST among them. The aim is to explore through a developed cellular automaton model of primary succession based on random establishment and climatic controls of recovery rates the potential timing of succession on primary surfaces against a speciation probability model of an evolving isolated mammal population. The results are compared and validated by the literature in addition to measured and described sequences of paleosols above and below ash deposits in central Oregon. Thus far, results suggest that rates of recovery are much greater than mammalian origination rates determined by the fossil record, genetics, and island evolution. Additionally, the preliminary results of this study do not reveal anything regarding the potential affects of volcanic eruptions on ecological relationships.