CONNECTIONS BETWEEN ECOLOGY, BIOGEOGRAPHY, AND PALEOBIOLOGY - RELATIONSHIP BETWEEN LOCAL ABUNDANCE AND GEOGRAPHIC-DISTRIBUTION IN FOSSIL AND RECENT MOLLUSKS

We used data on Contemporary and Pleistocene molluscs at one site in t he Gulf of California to evaluate and extend earlier ideas about the r elationship between local abundance and geographic distribution. For e ach species whose shells occurred in one Recent and two Pleistocene de posits, we measured its abundance in the sample and relative latitudin al position within its contemporary geographic range. Species near the edges of their ranges showed uniformly low abundances, whereas those near the centres exhibited a wide range of abundances. Species near th e edges of their ranges also appear to have exhibited greater changes in abundance, including more colonization and extinction events, betwe en the Pleistocene interglacial sample and the Recent one. The constra int of location in the geographic range on maximal local and regional abundance appears to offer an example of a connection between patterns and processes on local, regional, and geographical scales. Characteri stics of community structure, such as relative abundance of individual species and frequency of local co-existence of multiple species. may be influenced by the location of the sample site with respect to the g eographic ranges of the constituent species. These results demonstrate emergent, statistical features of population ecology and community or ganization that are manifest over geographic space and evolutionary ti me.