2008 Student Research Conference:
21st Annual Student Research Conference

Effects of Phylogenetic Tree Topology and Local and Regional Species Richness on NRI and NTI Distributions
Bryan J. Hartwig
Dr. Jonathan C. Gering and Dr. Dean DeCock, Faculty Mentors

The Net Relatedness Index (NRI) and the Nearest Taxon Index (NTI) are two statistics used to quantify clustering and overdispersion in phylogenetic community ecology. The method of testing statistical significance for clustering or overdispersion is not consistent across studies, and varying thoughts on the distributions of NRI and NTI is the cause of this problem. In order to determine whether parametric or non-parametric tests should be used, we generated NRI and NTI values for a number of phylogenetic scenarios that reflected natural situations. We then tested the normality of the resulting distributions using the Shapiro-Wilk statistic. The majority of scenarios resulted in distributions that were non-normal. Moreover, the distributions were typically skewed and rarely contained 95% of the values within ±2 standard deviations. Therefore, only non-parametric tests should be used to determine the statistical significance of phylogenetic clustering and overdispersion.

Keywords: Phylogenetics, Ecology, Normality, Net relatedness index, Nearest taxon index

Topic(s):Statistics

Presentation Type: Poster

Session: 14-
Location: OP Lobby
Time: 

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