BIOTIC RECOVERIES FROM MASS EXTINCTIONS: INSIGHTS FROM EVOLUTIONARY INNOVATION

Biotic recoveries following mass extinctions involve the rebuilding of ecological communities following massive perturbations, and often display significant biological innovations. Consequently they serve as important systems to examine the interplay between the physical environment, genetics/development, and ecology in evolutionary innovation. Yet the analysis of the expansion of many clades reveals no close correlation between developmental and morphological inventions (to use an analogy from the study of techonological innovation) and their ecological spread as innovations. This seems to suggest that ecology is the most significant control in innovation, a view incorporated in many models. But most models of post-extinction recovery are modifications of a simple logistic growth model, implicitly assuming the existence of ecological niches independent of any species occupying the niche (an assumption most ecologists realize is invalid). Applied to biotic recoveries, such models include an immediate biotic response following the end of the extinction, and logistic growth to a new equilibrium. The validity of several of these assumptions is questionable. New models of biotic recovery in which species construct their own niches, and involving positive feedback, show promise in more closely matching empirical studies of some post-extinction biotic recoveries. The study of biotic recoveries serves as an important testing ground for the study of evolutionary innovations. Most discussions of evolutionary innovation fall into two classes: key innovation models and open ecospace models. Each involve access to previously unavailable resources. In the first, the appearance of a new feature drives acquisition. In the second, an underutilized resource is made available, perhaps through occupation of a new offshore island, or following mass extinction. Both models follow the standard view of: "genetic/development proposes, ecology disposes." A constructionist view of biotic recoveries suggests a need to modify this approach to evolutionary innovations, with development and ecology constructing aspects of the environment and thus the ecological niches. Such a perspective has implications for major evolutionary transitions.