HERITABILITY, DIVERSIFICATION, AND THE MACROEVOLUTION OF HABITAT AFFINITY

All macroevolutionary patterns are due to the summed effects of many independent processes. Habitat affinity, the tendency for genera to specialize on one or another habitat, is no different. Here we focus on substrate affinity. Genera either love living in carbonates, siliciclastics, or they show no preference. We use a quantitative macroevolutionary theory that relates the change in a trait to the differential diversification association with traits and those traits heritability, which is itself a function of any tendency to change traits over phyletic time and between ancestor and descendant genera. Direct estimates of heritability are hampered due to the lack of a comprehensive phylogenetic framework for marine invertebrates. We can, however, use our theory to indirectly estimate heritability by comparing the observed changes in frequency to that expected by differential diversification alone. With high heritability a tight one-to-one regression is expected between the change in the average preferred habitat and the magnitude and direction of differential diversification; any change in the average habitat is fully attributable to the lovers of each habitat diversifying at different rates. A lower heritability will weaken this correlation and widespread switching of affinities will produce a negative correlation. We observe low levels of heritability with an average magnitude of 0.019. Heritability is variable over the Phanerozoic, with the largest positive and negative excursions occurring in the middle to late Paleozoic. These results imply that for most of the Phanerozoic, changes in the habitat affinity over time are due primarily to a tendency for new genera to originate in less popular habitats.