Factors influencing changes in trait correlations across species after using phylogenetic independent contrasts
- 291 Downloads
Comparative interspecific data sets have been analyzed routinely by phylogenetic methods, generally using Felsenstein’s phylogenetic independent contrasts (PIC) method. However, some authors have suggested that it may not be always necessary to incorporate phylogenetic information into statistical analyses of comparative data due to the low influence of shared history on the distribution of␣character states. The main goal of this paper was to undertake a comparison of results from non-phylogenetic Pearson correlation of tip values (TIPs) and phylogenetic independent contrasts analyses (PICs), using 566 correlation coefficients derived from 65 published papers. From each study we collected the following data: taxonomic group, number of species, type of phylogeny, number of polytomies in the phylogenetic tree, if branch length was transformed or not, trait types, the original correlation coefficient between the traits (TIPs) and the correlation coefficient between the traits using the independent contrasts method (PICs). The slope estimated from a regression of PIC correlations on TIP correlations was lower than one, and a paired t-test showed that correlations from PIC are significantly smaller than those obtained by TIP. Thus, PIC analyses tend to decrease the correlation between traits and usually increases the P-value and, thus, favoring the acceptance of the null hypothesis. Multiple factors, including taxonomic group, trait type and use of branch length transformations affected the change in decision regarding the acceptance of the null hypotheses and differences between PIC and TIP results. Due to the variety of factors affecting the differences between results provided by these methods, we suggest that comparative methods should be applied as a conservative approach to cross-species studies. Despite difficulties in quantifying precisely why these factors affect the differences between PIC and TIP, we also suggest that a better evaluation of evolutionary models underlying trait evolution is still necessary in this context and might explain some of the observed patterns.
KeywordsPhylogenetic independent contrasts method Felsenstein Phylogenetic signal Branch transformation Brownian motion Trait category
Unable to display preview. Download preview PDF.
We thank T. Garland Jr, D. Ackerly, M. van Kleunen and an anonymous reviewer for critical reading of previous versions of the manuscript. J.A.F. Diniz-Filho and L.M. Bini were supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), the Coordenação para Aperfeiçoamento do Ensino Superior (CAPES) and by FUNAPE of the Universidade Federal de Goiás. Priscilla Carvalho received a scholarship from CAPES.
- Ackerly DD (1999) Comparative plant ecology and the role of phylogenetic information. In: Press MC, Scholes JD, Barker, MG (eds) Physiological plant ecology. Blackwell Science, pp391–413Google Scholar
- Bennett PM, Owens IPF (2002) Evolutionary ecology of birds: life histories, mating systems an extinction. Oxford University Press, New YorkGoogle Scholar
- Björklund M (1997) Are “comparative methods” always necessary? Oikos 80:607–612Google Scholar
- Garland T Jr, Adolph SC (1994) Why not to do two-species comparative studies: limitations on inferring adaptation. Physiol Zool 67:797–828Google Scholar
- Gittleman JL, Anderson CG, Kot M, Luh H-K (1996) Phylogenetic lability and rates of evolution: a comparison of behavioral, morphological and life history traits. In: Martins EP (ed) Phylogenies and the comparative method in animal behavior. Oxford University Press, pp166–205Google Scholar
- Harvey PH, Pagel MD (1991) The comparative method in evolutionary biology. Oxford University PressGoogle Scholar
- Manly BFJ (1994). The design and analysis of research studies. Cambridge University Press,CambridgeGoogle Scholar
- Martins EP, Hansen TF (1996) The statistical analysis of interspecific data: a review and evaluation of phylogenetic comparative methods. In: Martins EP (ed) Phylogenies and the comparative method in animal behavior, Oxford University Press, pp22–75Google Scholar
- Peters RH (1993) The ecological implications of body size. Cambridge University Press, CambridgeGoogle Scholar
- Rezende EL, Garland T Jr (2003) Comparaciones interespecíficas y métodos estadísticos filogenéticos. In: F Bozinovic (eds) Fisiología Ecológica & Evolutiva. Teoría y casos de estudios en animals. Ediciones Universidad Católica de Chile, Santiago, pp79–98Google Scholar
- Ricklefs RE, Starck JM (1996) Applications of phylogenetically independent contrasts: a mixed progress report. Oikos 77:167–172Google Scholar
- Sokal RR, Rohlf FJ (1995) Biometry. WH Freeman and Company, New YorkGoogle Scholar
- Weathers WW, Siegel RB (1995) Body size establishes the scaling of avian postnatal metabolic rate: an interspecific analysis using phylogenetically independent contrasts. Ibis 137:532–542Google Scholar