ISLAND BIOGEOGRAPHY AND PALAEOBIOLOGY: IN SEARCH FOR EVOLUTIONARY EQUILIBRIA

Abstract

Summary1. The concept of evolutionary equilibrium has been derived from the theory of island biogeography via an ecological rationale for increase in species extinction rate and decrease in speciation rate with increasing diversity of the system.2. This concept is theoretically plausible at the species level and at a regional scale but, in spite of several empirical tests in the fossil record, it has thus far remained unsupported by empirical evidence. In order to test it conclusively, one has to analyze not only the pattern of species number through time but also its relationship to speciation and species extinction rates; independent evidence for perturbations must also be available.3. The concept of evolutionary equilibrium at the global scale must be extrapolated over higher levels of taxonomic hierarchy, for reliable species‐level data are unavailable at this scale. A theoretical justification for this concept cannot, then, be derived from the theory of island biogeography.4. The rates of family extinction and origination in the Phanerozoic show no evidence for diversity‐dependence, which undermines most quantitative models of biotic diversification based on the concept of global evolutionary equilibrium. Rigorous testing of these models cannot be done at the present state of knowledge because of the uncertainty about the empirical pattern (sampling and taxonomic biases, absolute time scale).