The evolution and emergence of paleocommunity resistance to secondary extinctions: Species and community level processes

Recent models of paleocommunity food webs confirm the potential of environmental disruptions to propagate devastating cascades of secondary extinction throughout communities. Application of the models to a series of Permian-Triassic terrestrial communities reveal a fundamental tension between species evolution, species properties and community properties. These relationships were examined in Late Permian pre-extinction terrestrial communities from the Karoo Basin of South Africa, and Early Triassic post-extinction communities. Late Permian communities were amniote-dominated, highly structured and resistant to secondary extinction, while Early Triassic recovery communities were amphibian-dominated and more susceptible. Subsequent recovery during the Early Triassic saw a return to the structured, amniote-dominated community type. Study of the pathways to recovery of both systematic and ecological diversity should be informative of the development of resistance and long-term stability in these communities. While the diversification of lineages within community guilds promotes, and is promoted by, species specialization, trophically generalized species are more resistant to secondary extinction. Nevertheless, trophically broad guilds that increase community connectance, also increase the propagation of secondary extinction. Recognition of the role of community structure in resistance to perturbation on geological timescales raises the possibility of community-level selection. Although community properties emerge from species properties, highly adapted species may become embedded over time in communities that are especially vulnerable during times of mass extinction. Understanding the relationships between species evolution, the emergence of community structure and dynamics from species interactions, and the resistance of communities during times of extreme perturbation, requires exploration of an unified microevolutionary, macroevolutionary, and paleoecological framework.