The relative influences of exotic species and environmental factors |
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Authors: | Francisco Nunes Godinho Maria Teresa Ferreira |
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Institution: | 1. Esta??o Florestal Nacional, Posto Apícola, Tapada da Ajuda, 1300, Lisboa, Portugal 2. Departamento de Engenharia Florestal, Instituto Superior de Agronomia, Tapada da Ajuda, 1399, Lisboa, Portugal
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Abstract: | Spatial variation in the native fish community of the lower Guadiana basin (southern Iberia) was related to both biotic (abundance
of exotic species) and environmental factors using canonical correspondence analysis, CCA. After choosing the best predictors
among the environmental and biotic variables, we partitioned the total variation in native species abundances (18 species-size
combinations by 44 sampling locations matrix) into that accounted for (1) solely by selected environmental variables, (2)
solely by selected biotic variables, (3) by both environmental and biotic variables together, and (4) that unexplained. Of
the 22 variables initially considered in the environmental CCA, only RIVER (dummy variable codifying sampling locations belonging
to the main river), SALT (dummy variable codifying sampling locations belonging to tributaries that discharge to the brackish
Guadiana), substrate heterogeneity, and macrobenthos abundance were selected as best predictors. In the biotic CCA, three
species-size combinations were selected from the eight considered: Micropterus salmoides > 150 mm in total length (TL), Lepomis
gibbosus > 100 mm in TL and Gambusia holbrooki. The total variation in the native fish community was partitioned into the
following components: pure environmental (24.4%), pure biotic (12.4%), shared (9.2%) and unexplained (54.0%). There was a
significant influence of exotic fish on native community variation after accounting for the effect of environmental factors.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | river environment endemism spatial organisation biotic interactions canonical correspondence analysis Portugal |
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