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extinction is worth exploring, as are species-energy relationships (Evans et al., 2005; Hawkins et al., 2007a).

Ecological networks also provide a host of services to the community, ranging from clean water to fine-scale modification of climate (microhabitats). These ecological services have been a subject of considerable interest among conservation biologists, but have not been addressed in deep time. For example, what was the impact on the water quality in shallow marine ecosystems as a consequence of the loss of so many articulate brachiopods, crinoids, bryozoans, and other filter feeders during the end-Permian mass extinction? This issue is probably best investigated through stable isotope studies of nutrient flow or geochemical cycling (West et al., 2006) or where the services leave a tangible fossil record.

Architectural Diversity and Ecosystem Engineering

The framework of modern reefs is generated by scleractinian corals, with a significant contribution from coralline algae and early diagenetic cements. Architecturally similar structures, at least at a gross scale, have been built by microbial communities, sponges and archaeocyathids, tabulate and rugose corals, stomatoporoids, bryozoans, brachiopods, and rudist bivalves. Reefs are a specific example of the provisioning of architectural diversity, which can provide a positive feedback on biodiversity. Such ecosystem engineering allows species to modify the environment in ways that can affect, either positively or negatively, resource availability for other species (Jones et al., 1997). A related concept is niche construction, in which species modify their own environment in a way that influences the fitness of the population and, through ecological inheritance, the fitness of subsequent generations (Odling-Smee et al., 2003). Although ecosystem engineering can be recognized in the fossil record, identifying niche construction requires an understanding of selection pressures that is generally more difficult for paleontologists. Both niche construction and ecosystem engineering are currently the subject of considerable investigation and appear to have significant implications for macroevolution (Erwin, 2008).

Reef ecosystems provide a clear example where the loss of the 3D complexity of the reef has a strong negative impact on biodiversity. Kiessling (2005) showed that over million-year periods high biodiversity on reefs is related to stability, as measured by the density of skeletal organisms, the style of reef building, and the types of biotic reefs. Some mass extinction events destroy this buffering from environmental fluctuations. The composition and consequent fabric of reefs has undergone considerable variation during the 543 Ma of the Phanerozoic (Wood, 1999; Kiessling, 2002). The structure of Early Cambrian to Early Ordovician reefs was



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