Cretaceous CO2 Decline and the Radiation and Diversification of Angiosperms

Abstract

7.1 Introduction Determining how a projected doubling of atmospheric CO 2 concentration by the end of this century (IPCC 2001) will influence species composition and biodiv-ersity remains a major scientific and political challenge (Loreau et al. 2001). Long-term CO 2 experiments using FACE (free air carbon dioxide enrichment) now yield invaluable results on how forests and crops/grassland vegetation re-spond in terms of their biomass allocation, productivity, light use, water use, and nutrient use efficiency in elevated CO 2 (500–700 ppm) (DeLucia et al. 1999; McLeod and Long 1999; Oren 2001). Furthermore, related experimental ap-proaches are increasing our understanding of plant reproductive responses (Hussain, Kubiske, and Connor 2001) and competitive interactions (Bazzaz et al. 1995) in high CO 2 conditions. However, the current spatial and temporal scale of these experiments (Ͻ10 years) are limited and cannot yet take into consideration the floristic changes that may result from continuing increases in anthropogenic CO 2 at the ecosystem or biome level. Such floristic and macro-ecological data are readily available from the plant fossil record on timescales of millions of years and on spatial scales spanning whole continents. In this chapter we investigate the effects of long-term fluctuations in atmospheric CO 2 concentration during the Cretaceous period (145–65 Ma) (Tajika 1998; 1999) on patterns of ecological dominance and taxonomic diversity in Cretaceous fossil floras. In particular, we test the hypothesis of Teslenko (1967) and Robinson 134 J.C. McElwain et al. (1994) that " CO 2 starvation " during the Cretaceous contributed to the taxonomic diversification and ecological radiation of angiosperms.