Microevolutionary Implications Of Clinal Variation In The Paleozoic Bryozoan Streblotrypa

Ideally, studies of microevolution, including those of patterns and rates of speciation, need to account for features of geographic and ecophenotypic morphologic variation. These factors can provide primary sources of variation for evolution to act upon. They can also, however, produce variation among characters that are not directly related to speciation events, thus confounding recognition of larger evolutionary patterns. Because of limitations of geologic settings, features of morphologic variation associated with geographic and ecophenotypic variation are difficult to constrain and are often neglected. Consequences of ignoring potential geographic variation in microevolutionary studies are varied. The likelihood of observing stasis or gradation may increase or decrease depending on initial assumptions. A series of tests that place reasonable limits on potential errors, however, can strengthen conclusions from empirical microevolutionary studies. Late Paleozoic cyclothems of the North American Midcontinent provide an excellent opportunity to study patterns of microevolution and concomitant ecophenotypic and geographic variation.