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P-type based dimensionality reduction for open contours of Colombian Páramo plant species

Berdugo-Lattke, Mary Lee, Gónzalez, Fabio, Rangel-Ch, J. Orlando, Gómez, Francisco
Ecological informatics 2016 v.36 pp. 1-7
ecosystems, expert opinion, forests, indigenous species, petioles, principal component analysis, treeline
Páramos are a biome above the forest tree-line characterized by high native vegetation diversity. In recent years, several biota and environmental features of the Colombian Páramos have been described. Nevertheless, despite these advances, many relevant features such as leaf morphoecology of Páramo vegetation remain poorly understood. In particular, leaf morphology in Páramo plants has been sparsely described. Traditionally, leaf morphological description has been based on visual categorical systems, which can be highly biased by expert's opinion. In recent years, an objective method based on elliptic Fourier transforms and Principal Component Analysis (PCA) has been adopted by ecologists and phytologists to quantitatively assess leaf shape morphology. This approach is critically held on the idea that the leaf margin can be described as a closed contour, although, such assumption is not satisfied by several Páramo plant species because a considerable percentage of them are characterized by sessile leaves, i.e., leaves without petiole. Sessile leaves can be only described by using open contours. In this work, we propose a shape description for open contours based on p-type Fourier representations and PCA. The method was evaluated on 115 Páramo leaves from 12 species and compared with related approaches. The results show that the proposed method is able to capture high levels of variability and improve the mathematic representation of shape when compared to conventional methods based on simple geometrical quantities and elliptic Fourier transform descriptors.