Selecting Variables for Habitat Suitability of <Emphasis Type="Italic">Asellus</Emphasis> (Crustacea,Isopoda) by Applying Input Variable Contribution Methods to Artificial Neural Network Models |
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Authors: | Ans M Mouton Andy P Dedecker Sovan Lek Peter L M Goethals |
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Institution: | (1) Department of Applied Ecology and Environmental Biology, Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, J. Plateaustraat 22, 9000 Ghent, Belgium;(2) Flemish Environment Agency, Zandvoordestraat 375, 8400 Ostend, Belgium;(3) LADYBIO UMR 5172, CNRS-University Paul Sabatier, 118, route de Narbonne, 31062 Toulouse, France;(4) Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, J. Plateaustraat 22, 9000 Ghent, Belgium |
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Abstract: | This study aimed to compare different methods to analyse the contribution of individual river characteristics to predict the
abundance of Asellus (Crustacea, Isopoda). Six methods which provide the relative contribution and/or the contribution profile of the input variables
of artificial neural network models were therefore compared: (1) the ‘partial derivatives’ method; (2) the ‘weights’ method;
(3) the ‘perturb’ method; (4) the ‘profile’ method; (5) the ‘classical stepwise’ method; (6) the ‘improved stepwise’ method.
Consequently, the key variables which affect the habitat preferences of Asellus could be identified. To evaluate the performance of the artificial neural network model, the model predictions were compared
with the results of a multiple linear regression analysis. The dataset consisted of 179 samples, collected over a 3-year period
in the Zwalm catchment in Flanders, Belgium. Twenty-four environmental variables as well as the log-transformed abundance
of Asellus were used in this study. The different contribution methods seemed to give similar results concerning the order of importance
of the input variables. Nevertheless, their diverse computation led to differences in sensitivity and stability of the methods
and the derived outcomes on the habitat preferences. From an ecological point of view, the environmental variables describing
the stream type (width, depth, stream order and distance to mouth) were the most significant variables for Asellus in the Zwalm catchment during the period 2000–2002 for all applied methods. Indirectly, one can conclude that the water quality
is not the limiting factor for the survival of Asellus in the Zwalm catchment. |
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