Published online by Cambridge University Press: 05 July 2014
Introduction
Evolutionary history is characterised by numerous occurrences of ‘double-wedge’ patterns of diversification and decline, wherein one taxon rises in diversity, but then declines alongside an increase in diversity of a second group (Figure 11.1). In some instances, temporal overlap of these two diversity curves has been taken to imply competitive replacement. In a review of the subject, Benton (1987) discussed the problem of distinguishing true competitive replacement from turnover events that result from some extrinsic factor such as environmental change. This distinction between intrinsic and extrinsic factors is at the heart of the debate over detection of competition in the fossil record.
Intrinsic factors imply a competitive advantage that one group has over another, but defining that advantage is difficult. Replacement can be caused by direct competition, such as uneven resource gathering capabilities (Sepkoski, 1996; Schluter, 2000) or interference competition (e.g. carcass theft and interspecific killing) (Palomares and Caro, 1999; Van Valkenburgh, 2001). The successful group in this direct competition may possess an adaptation (Rosenzweig and McCord, 1991) that allows it to outcompete the declining group. Benton (1987) termed turnover events derived from direct competition ‘active replacement’ or ‘ecological replacement’, and found very few convincing cases in the literature for this type of replacement (Benton, 1996).
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