Correlations and co-occurrences of taxa:
the role of temporal, geographic, and taxonomic restrictions

Aleksi Kallio, Kai Puolamäki, Mikael Fortelius, and Heikki Mannila

ABSTRACT

Correlation between occurrences of taxa is a fundamental concept in the analysis of presence-absence data. Such correlations can result from ecologically relevant processes, such as existence and evolution of species communities. Correlations are typically quantified by some sort of similarity index based on co-occurrence counts. We argue that the individual values of a similarity index are not useful as such: rather, we have to be able to estimate the statistical significance of the index value. Secondly, we argue that before computing the correlations one has to carefully select what is the underlying base set of locations for which the co-occurrence counts, similarity indices, and their significance is computed. We demonstrate base set selection with synthetic examples and conclude with an analysis of real data from a large database of fossil land mammals.

*Aleksi Kallio. CSC - IT Center for Science Ltd. P.O. Box 405, FI-02101 Espoo, Finland.
*Kai Puolamäki. Aalto University, Department of Information and Computer Science and HIIT Helsinki Institute for Information Technology.P.O. Box 15400, FI-00076 Aalto, Finland.
Mikael Fortelius. University of Helsinki, Department of Geosciences and Geography
P.O. Box 64, 00014 University of Helsinki, Finland.
Heikki Mannila. Aalto University, Department of Information and Computer Science and HIIT Helsinki Institute for Information Technology. P.O. Box 15400, FI-00076 Aalto, Finland.
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* These authors contributed equally to the work.

KEYWORDS: correlation; co-occurrence; base set; similarity index; statistical significance

PE Article Number: 14.1.4A
Copyright: Society for Vertebrate Paleontology March 2011
Submission: 15 October 2009. Acceptance: 28 November 2010