Impact of the Paleocene-Eocene thermal maximum on deep-ocean microbenthic community structure: Using rank-abundance curves to quantify paleoecological response

The Paleocene-Eocene thermal maximum (PETM) has been attributed to the rapid release of approximately 2000 x 10(9) metric tons of carbon in the form of methane. In theory, oxidation and ocean absorption of this carbon should have lowered deep-sea pH, thereby triggering a rapid ( 100,000 years). These findings indicate that a large mass of carbon (>2000 x 10(9) metric tons of carbon) dissolved in the ocean at the Paleocene-Eocene boundary and that permanent sequestration of this carbon occurred through silicate weathering feedback.

Most plant communities consist of several or many species which compete for light, water, and nutrients. Species in a given community may be ranked by their relative success in competition; productivity seems to be the best measure of their success or importance in the community. Curves of decreasing productivity connect the few most important species (the dominants) with a larger number of species of intermediate importance (whose number primarily determines the community's diversity or richness in species) and a smaller number of rare species. These curves are of varied forms and are believed to express different patterns of competition and niche differentiation in communities. It is probably true of plants, as of animals, that no two species in a stable community occupy the same niche. Evolution of niche differentiation makes possible the occurrence together of many plant species which are partial, rather than direct, competitors. Species tend to evolve also toward habitat differentiation, toward scattering of their centers of maximum population density in relation to environmental gradients, so that few species are competing with one another in their population centers. Evolution of both niche and habitat differentiation permits many species to exist together in communities as partial competitors, with distributions broadly and continuously overlapping, forming the landscape's many intergrading communities.