title: Tuning the Voices of a Choir: Detecting Ecological Gradients in Time-Series Populations.
abstract: This paper introduces a new approach-the Principal Component Gradient Analysis (PCGA)-to detect ecological gradients in time-series populations, i.e. several time-series originating from different individuals of a population. Detection of ecological gradients is of particular importance when dealing with time-series from heterogeneous populations which express differing trends. PCGA makes use of polar coordinates of loadings from the first two axes obtained by principal component analysis (PCA) to define groups of similar trends. Based on the mean inter-series correlation (rbar) the gain of increasing a common underlying signal by PCGA groups is quantified using Monte Carlo Simulations. In terms of validation PCGA is compared to three other existing approaches. Focusing on dendrochronological examples, PCGA is shown to correctly determine population gradients and in particular cases to be advantageous over other considered methods. Furthermore, PCGA groups in each example allowed for enhancing the strength of a common underlying signal and comparably well as hierarchical cluster analysis. Our results indicate that PCGA potentially allows for a better understanding of mechanisms causing time-series population gradients as well as objectively enhancing the performance of climate transfer functions in dendroclimatology. While our examples highlight the relevance of PCGA to the field of dendrochronology, we believe that also other disciplines working with data of comparable structure may benefit from PCGA.
authors.affiliation: Institute of Botany and Landscape Ecology, Ernst-Moritz-Arndt-Universität, Soldmannstraße 15, 17487 Greifswald, Germany.
authors.forename: Allan
authors.initials: A
authors.lastname: Buras
authors.affiliation: Institute of Botany and Landscape Ecology, Ernst-Moritz-Arndt-Universität, Soldmannstraße 15, 17487 Greifswald, Germany.
authors.forename: Marieke
authors.initials: M
authors.lastname: van der Maaten-Theunissen
authors.affiliation: Institute of Botany and Landscape Ecology, Ernst-Moritz-Arndt-Universität, Soldmannstraße 15, 17487 Greifswald, Germany.
authors.forename: Ernst
authors.initials: E
authors.lastname: van der Maaten
authors.affiliation: Institute of Botany and Landscape Ecology, Ernst-Moritz-Arndt-Universität, Soldmannstraße 15, 17487 Greifswald, Germany.
authors.forename: Svenja
authors.initials: S
authors.lastname: Ahlgrimm
authors.affiliation: Institute of Botany and Landscape Ecology, Ernst-Moritz-Arndt-Universität, Soldmannstraße 15, 17487 Greifswald, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Hermann
authors.affiliation: GFZ German Research Centre for Geosciences, Section 5.2, Telegrafenberg, 14473 Potsdam, Germany.
authors.forename: Sonia
authors.initials: S
authors.lastname: Simard
authors.affiliation: GFZ German Research Centre for Geosciences, Section 5.2, Telegrafenberg, 14473 Potsdam, Germany.
authors.forename: Ingo
authors.initials: I
authors.lastname: Heinrich
authors.affiliation: GFZ German Research Centre for Geosciences, Section 5.2, Telegrafenberg, 14473 Potsdam, Germany.
authors.forename: Gerd
authors.initials: G
authors.lastname: Helle
authors.affiliation: Institute of Botany and Landscape Ecology, Ernst-Moritz-Arndt-Universität, Soldmannstraße 15, 17487 Greifswald, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Unterseher
authors.affiliation: Institute of Botany and Landscape Ecology, Ernst-Moritz-Arndt-Universität, Soldmannstraße 15, 17487 Greifswald, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Schnittler
authors.affiliation: Institute of Botany and Landscape Ecology, Ernst-Moritz-Arndt-Universität, Soldmannstraße 15, 17487 Greifswald, Germany.
authors.forename: Pascal
authors.initials: P
authors.lastname: Eusemann
authors.affiliation: Institute of Botany and Landscape Ecology, Ernst-Moritz-Arndt-Universität, Soldmannstraße 15, 17487 Greifswald, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Wilmking
mesh_terms: D004463:Ecology; D009010:Monte Carlo Method; D025341:Principal Component Analysis