RATES OF ECOLOGICAL CHANGE OF MARINE BENTHIC INVERTEBRATES DURING DIFFERENT CLIMATE STATES

Little is known about how rates of ecological change are influenced by climate over geological time scales, despite the importance for providing the historical context of the biotic response to anthropogenic warming. We hypothesize that rates of ecological change were faster during warm climates, because evolutionary rates, to which they are precursors, seem to have been particularly slow during cold global climates such as the late Paleozoic ice age, and in cold polar regions of the present day compared to the tropics. To test this hypothesis, we collected marine benthic invertebrate fossils from measured sections of the late Ordovician Reedsville Formation of central Pennsylvania, and compared the observed rate of change over this 6-7 m.y. interval to literature-derived data from other communities that lived in similar environments (muddy foreland basins) but different global climates. We calculated ecological rates by ordinating our abundance data using non-metric multidimensional scaling and plotting the resulting scores against stratigraphic position. Over most of the Reedsville interval, marine community composition and structure is very stable. By comparison, greater rates of change were observed in middle and late Devonian communities, which lived during a somewhat cooler global climate. These patterns preliminarily indicate that ecological rates of change are dependent on global climate, although apparently not in the same direction as evolutionary rates.