期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：23
页码：7207-7212
DOI：10.1073/pnas.1422248112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceGlobal change and regime shifts of ecosystems are a major concern today. It has been suggested that the end-Cretaceous impact of an asteroid not only caused mass extinction but also involved the transgression of a global tipping point. We demonstrate that the ecological structure of pre- and postextinction assemblages of marine bivalves and gastropods differ far more than expected from usual background fluctuations. In-depth ecological analyses suggest site-specific rather than globally uniform shifts to different dynamic regimes. At more inclusive ecological levels, parallel increases emerge in mobility levels, in species burrowing into the sediment, and in deposit feeders and carnivores. Contemporary biodiversity loss and population declines threaten to push the biosphere toward a tipping point with irreversible effects on ecosystem composition and function. As a potential example of a global-scale regime shift in the geological past, we assessed ecological changes across the end-Cretaceous mass extinction based on molluscan assemblages at four well-studied sites. By contrasting preextinction and postextinction rank abundance and numerical abundance in 19 molluscan modes of life--each defined as a unique combination of mobility level, feeding mode, and position relative to the substrate--we find distinct shifts in ecospace utilization, which significantly exceed predictions from null models. The magnitude of change in functional traits relative to normal temporal fluctuations at far-flung sites indicates that molluscan assemblages shifted to differently structured systems and faunal response was global. The strengths of temporal ecological shifts, however, are mostly within the range of preextinction site-to-site variability, demonstrating that local ecological turnover was similar to geographic variation over a broad latitudinal range. In conjunction with varied site-specific temporal patterns of individual modes of life, these spatial and temporal heterogeneities argue against a concerted phase shift of molluscan assemblages from one well-defined regime to another. At a broader ecological level, by contrast, congruent tendencies emerge and suggest deterministic processes. These patterns comprise the well-known increase of deposit-feeding mollusks in postextinction assemblages and increases in predators and predator-resistant modes of life, i.e., those characterized by elevated mobility and infaunal life habits.
关键词：end-Cretaceous mass extinction ; regime shift ; functional groups ; mollusks ; ecospace
