NACODE (NORTH AMERICAN COMBINED OSTRACODE DATABASE); INTRODUCTION AND APPLICATION

The North American Combined Ostracode Database (NACODe) currently under development comprises ostracode occurrence, environmental, and climatic data from Canada (Delorme Database, >6,700 sites, housed in the Canadian Museum of Nature, Ottawa) and the United States of America (North American Nonmarine Ostracode Database, approximately 600 sites, housed at Kent State Univ., Ohio). NACODe’s ostracod data are binary (present/not present) and include 108 species with 3 or more occurrences, from 34 genera. Biogeographic maps based on NACODe show the northern and southern distributional limits of several species, likely reflecting thermal (e.g. Mean Annual Air Temperature) boundaries. For others only northern (thermal) limits are indicated or their distributions extend beyond the confines of the dataset. Hydrochemical limits are verified for some species, such as Limnocythere sappaensis and L. stapliniwhich respectively prefer waters enriched in either bicarbonate or calcium ions. The combined datasets capture more fully the range of physicochemical characteristics of ostracod species' host water than either of the component databases, facilitating improved palaeohydrochemical and palaeoclimatic reconstructions.

However, NACODe’s environmental data distribution is near-Gaussian, and thus requires a data density adjustment. The simple reason for this processing is that the dataset has more opportunities for ostracode occurrence in environments with modal values, but increasingly fewer opportunities greater or less than the mode. The adjustments are greater the further the mean environmental value is away from the database mode. For example, halophylic species such as Limnocythere staplini and Candona patzcuaro occur in sites with respective mean log (TDS) values of 10^3.8 and 10^2.6 mg/L (6,309 and 398 mg/L), but have density modes of about 10^4.5 mg/L (~31,500 mg/L). On the other hand, Cypria ophthalmica and Candona elliptica occur at sites with respective mean log (TDS) values of about 10^2.1 mg/L and 10^2.0 mg/L (125 and 100 mg/L), and an adjusted density means of 10^1.4 mg/L (25 mg/L) and 10^1.7 mg/L (50 mg/L).