Phanerozoic diversity and neutral theory

Although Phanerozoic increases in the global richness, local richness, and evenness of marine invertebrates are well documented, a common explanation for these patterns has been difficult to identify. Evidence is presented here from marine invertebrate communities that there is a Phanerozoic increase in the fundamental biodiversity number (θ), which describes diversity and relative abundance distributions in neutral ecological theory. If marine ecosystems behave according to the rules of Hubbell’s Neutral Theory of Biodiversity and Biogeography, the Phanerozoic increase in θ suggests three possible mechanisms for the parallel increases in global richness, local richness, and evenness: (1) an increase in the per-individual probability of speciation, (2) an increase in the area occupied by marine metacommunities, and (3) an increase in the density (per-area abundance) of marine organisms. Because speciation rates have declined over time and because there is no clear evidence for an increa...