EXPLORING THE RELATIONSHIPS AMONG MOLLUSK COMMUNITY CHANGE AND THE TEMPO AND MODE OF SPECIATION IN THE UPPER GURABO FORMATION (NEOGENE, DOMINICAN REPUBLIC)

A central question in evolutionary biology is whether community-level processes facilitate, maintain, or constrain the tempo and mode of species-level evolutionary change. The fossil record of abundant and well-preserved invertebrates from the Neogene of the Dominican Republic has been central to several investigations of the tempo and mode of speciation. Nevertheless, the community ecological contexts of these speciation events remain unstudied despite more than 20 years of systematic and taxonomic studies of the associated Dominican invertebrate fauna. Thus, paleobiologists have not been able to determine how or if community-level processes promoted or limited speciation in these well-known and extensively studied stratigraphic sections. This study has three goals: (1) document and quantitatively compare mollusk communities through time in the deep marine upper Gurabo Formation (from 375 m to 405 m in the section); (2) increase the precision of large-scale paleoenvironmental interpretations using sedimentary and faunal indicators; and (3) compare previously-documented species-level evolutionary patterns in the section to mollusk community change. We collected 18 bulk samples (~3 Kg/2.8 L) from NMB localities 15805, 15809, 15966, 15913, and 15934/5, which are located within 375 m to 405 m in the section. Samples were soaked and then washed through sediment sieves. All identifiable specimens > 3.0 mm were sorted and identified to the species level. Specimen relative abundances and species richness data were analyzed using MDS in PC-ORD v4.0 and Analytic Rarefaction v1.3 (Holland, 2003). We found: (1) significantly different mollusk communities and species richness values occur among samples in the upper Gurabo Formation; (2) significant environmental variation occurs within the deep marine part of the section; and (3) gradual but oscillatory morphological evolution in Prunum does not appear to be closely linked to mollusk community change in the upper Gurabo Formation.