USING GIS TO ASSESS THE BIOGEOGRAPHIC IMPACT OF SPECIES INVASIONS
ON NATIVE BRACHIOPODS DURING THE RICHMONDIAN INVASION IN THE
TYPE-CINCINNATIAN (LATE ORDOVICIAN, CINCINNATI REGION)

Alycia L. Stigall

ABSTRACT

The Late Ordovician age strata in the Cincinnati, Ohio, region record a dramatic immigration of exta-basinal taxa into the region, termed the Richmondian Invasion, at the Maysvillian/Richmondian Stage boundary. The effects of the species invasion on genus-level paleoecology and biodiversity are well characterized; however, no prior analyses have examined biogeographic patterns in terms of areal extent of geographic ranges at the level of individual species at fine spatial or temporal scales. Geographic ranges of rhynchonelliform brachiopod species and genera were reconstructed using GIS-generated bounding polygons for each of the six depositional sequences delineated within Cincinnatian strata in order assess biogeographic patterns before, during, and after the Richmondian Invasion. Taxa were divided into four groups for analyses: native species that become extinct in the Maysvillian, native species that persist into the Richmondian, new species evolving in the Richmondian from native ancestors, and interbasinal invaders. Several statistical patterns emerge: native species with larger ranges preferentially survive compared to those with smaller ranges; carryover taxa exhibit no significant change in range size following invasion; both carryover and invader taxa exhibit large geographic ranges characteristic of eurytopic taxa, whereas new species have small ranges and are ecological specialists. Invasive species, therefore, most profoundly impacted narrowly adapted, specialist species during the early stages of invasion. Ecosystem response to the invasion continued for at least one million years. Native generalist taxa occupied larger geographic ranges than invader taxa for the first million years of the invasion, indicating a limited role for competition in driving ecosystem change.

Alycia L. Stigall. Department of Geological Sciences and OHIO Center for Ecology and Evolutionary Studies, Ohio University, 316 Clippinger Laboratories, Athens, Ohio 45701 USA

Keywords: Ordovician, paleoecology, speciation, extinction, Katian

PE Article Number: 13.1.5A
Copyright: Paleontology Society March 2010
Submission: 22 July 2009. Acceptance: 27 January 2010