MOVING BEYOND BIAS: A MODEL FOR THE COMMON CAUSE OF EVOLUTIONARY AND STRATIGRAPHIC PATTERNS, BASED ON HUBBELL'S UNIFIED THEORY

Many macroevolutionary patterns correlate with the stratigraphic record of sea-level change. Although preservational biases alter this correlation through changes in rock volume as well as sequence stratigraphic architecture, the correlation may also reflect a common cause. Hubbell's Unified Neutral Theory of Biodiversity is used here to predict patterns of evolutionary and ecological change within systems tracts of depositional sequences, primarily through the effects of metacommunity size (Jm), the fundamental biodiversity number (theta), and migration rate (m).

Within a depositional sequence, the falling-stage systems tract typically records a reduction in shelf area, lowering both Jm and theta, decreasing both richness and evenness in the metacommunity. During the lowstand systems tract (LST), shelf area increases slowly, leading to a modest reversal of these patterns. During the transgressive systems tract (TST), shelf area soars, elevating Jm and theta, possibly at a rate that creates a nonequilibrial period in which zero-sum rules of assembly no longer hold. In addition, habitat heterogeneity increases in the LST and especially the TST, particularly substrate consistency in the marine realm and the compartmentalization of habitats in the coastal realm, both of which will lead to decreased m and increased isolation of local communities, with corresponding elevated abundances and community heterogeneity (increased beta diversity). Local communities in the TST should display low richness and evenness, whereas the metacommunity should display high richness and evenness. During the highstand systems tract (HST), shelf area decreases slowly, favoring relatively stable to slowly declining Jm and theta. Decrease in habitat heterogeneity in the HST will raise m, decrease the isolation of local communities, and consequently depress variance in abundance and the heterogeneity among communities. Variation in shelf morphology, the position of sea-level, and rate of sea-level change may generate exceptions to these general patterns.