Abstract
We propose a new graphical approach to the analysis of multi-temporal morphological and ecological data concerning the life history of fish, which can typically serves models in ecomorphological investigations because they often undergo significant ontogenetic changes. These changes can be very complex and difficult to describe, so that visualization, abstraction and interpretation of the underlying relationships are often impeded. Therefore, classic ecomorphological analyses of covariation between morphology and ecology, performed by means of multivariate techniques, may result in non-exhaustive models. The Self Organizing map (SOM) is a new, effective approach for pursuing this aim. In this paper, lateral outlines of larval stages of gilthead sea bream (Sparus aurata) and dusky grouper (Epinephelus marginatus) were recorded and broken down using by means of Elliptic Fourier Analysis (EFA). Gut contents of the same specimens were also collected and analyzed. Then, shape and trophic habits data were examined by SOM, which allows both a powerful visualization of shape changes and an easy comparison with trophic habit data, via their superimposition onto the trained SOM. Thus, the SOM provides a direct visual approach for matching morphological and ecological changes during fish ontogenesis. This method could be used as a tool to extract and investigate relationships between shape and other sinecological or environmental variables, which cannot be taken into account simultaneously using conventional statistical methods.
Highlights
Ecomorphology is a comparative discipline that investigates the relationship between shape and ecological features of organisms, species or communities [1]
Self - Organising Maps It is useful to inspect the result by firstly looking at the Self Organizing map (SOM) pattern, and adding the additional information provided by external descriptor
The outline prototypes represented an abstraction from the information stored in the input data, and their use allowed an effective visualization of shape diversity and variability
Summary
Ecomorphology is a comparative discipline that investigates the relationship between shape and ecological features of organisms, species or communities [1]. GM cannot be used when the number of utilizable landmarks that could be used is low (e.g. when fish larvae are studied), since it leads to non-exhaustive and balanced descriptions of shape [25] The latter approach is primarily represented by Elliptic Fourier Analysis (EFA) of outline, which allows changes in body profile through the entire ontogeny to be analysed. It should be stressed that it is possible to combine these two approaches into the recently developed methodology of semi landmarks [25,26], which is based on the detection and analysis of spaced landmarks along a curve joining two reference structures or surrounding a body part This approach is aimed at analysing curves in the same analytical framework as landmarks and does not offer advantages with respect to simple EFA if the object of the investigation is the overall shape of the organisms instead of those of single structures or body regions [25;26]. Applications of this approach to the study of relationships between shape and ecological characteristics are extensively reported in the literature [7;27,28,29,30]
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