THE CONTRASTING EFFECTS OF EXTINCTION ON TAXONOMIC AND ECOLOGICAL COMPOSITION: INITIAL RESULTS OF NUMERICAL EXPERIMENTS

Previous studies have shown that the taxonomic and ecological severity of an extinction event are not necessarily coupled: two extinctions of equal taxonomic loss may have substantially different ecological effects. Here, we present a numerical model that contrasts the ecological and taxonomic outcome of extinction across a range of extinction intensities.

Two scenarios are simulated: extinction that is non-selective across ecological guilds, and extinction that is selective. In each, a predetermined number of taxa are classified into ecological guilds. In the non-selective extinction model, each taxon is assigned a random probability of survival independent of their guild classification, while in the ecologically selective extinction, taxa are randomly given a greater or lesser chance of survival based on their guild membership. After creating the pre and post-extinction communities for both models, each community is sampled to generate a paleontological sample. Additive diversity of partitions of alpha diversity, beta diversity within facies, and beta diversity among facies are then calculated. For each percentage of extinction, these two models were repeated up to 10,000 times to generate the mean and confidence intervals on each diversity partition.

Preliminary results show that as extinction intensity increases the percentage contribution of alpha diversity increases while the percentage contribution of all levels of beta diversity decreases. Among taxa, little change is seen in alpha and beta diversity between the random model and the ecologically selective model at all extinction intensities. However, among guilds, the percent contribution of alpha diversity is greater during the ecologically selective extinction than the random extinction at the expense of beta diversity. In addition, comparisons of extinction intensity and proportion of surviving guilds shows that at moderate extinction intensities the proportions of surviving guilds differ greatly between the random and selective extinction models, but at low and high extinction intensities the proportion of surviving guilds is indistinguishable between the two models. Collectively, these experiments demonstrate a simple but effective test for ecological selectivity during extinction episodes.