Knowledge of species' ecological niches can be used to assess ecological interactions between different taxa. Sixteen species of cetaceans have been recorded in Galician waters and niche partitioning is expected to occur among these species in order to allow them to co-exist. In this study, the niches occupied by five of the most commonly encountered odontocete species off Galicia (NW Iberia) were compared, based on seven ecogeographic variables, using a PCA-based methodology and Classification trees. Significant differences in niche centres and niche widths were found among all the species. During the summer, the harbour porpoise occupied the narrowest and most differentiated niche when compared to the rest of the species. Three species could be compared during the winter, when long-finned pilot whales preferred colder and less variable water temperatures than did common dolphins. Seasonal differences in habitat preferences were found for bottlenose dolphins. A higher degree of specialisation was found during the summer, resulting in stronger differences in habitat use in this season, which may be related to an increment in resource availability during the upwelling period (April-September). The PCA-based methodology used in this study provides an effective multivariate approach to explore niche partitioning between co-existing species. (c) 2013 Elsevier Ltd. All rights reserved.
Bibliographical noteWe thank Andreas Palialexis at the Hellenic Centre of Marine Research and Dimitra Kitsiou and Zoi Pataki from the University of the Aegean for their help with data processing. Thanks to Karen Hall at the University of Aberdeen for useful comments during data analysis and discussion. The authors gratefully acknowledge the assistance of volunteers from CEMMA and IEO, especially Ángela Llavona, Jose M. Cedeira, Xulio Valeiras and Salvador García, for their help during data gathering. We also acknowledge the input of all enthusiastic marine mammal observers. Observers onboard fishing vessels were funded by the European Commission's Directorate General for Fisheries (Study Projects number 97/089, “Impact of fisheries on small cetaceans in coastal waters of Northwest Spain and Scotland” and number 00/027, “Pelagic fisheries in Scotland (UK) and Galicia (Spain): observer studies to collect fishery data and monitor by-catches of small cetaceans”) and the Xunta de Galicia (Project number PGIDIT02MA00702CT, 2002–2005, “Predictive system of fishing efforts for the Galician artisan fleet”). Surveys onboard the vessel Íbero were funded by Fundación La Caixa (Study project “A favour del Mar: la ruta del Íbero 2008”). R.F. was supported during the research period through a Marie Curie Early-Stage Research Grant (ECOSUMMER project. 020501-2) and an AXA Research Fund postdoctoral grant. G.J.P. was supported by the ANIMATE project (MEXC-CT-2006-042337). M.B.S. acknowledges support from the LOTOFPEL project (Plan Nacional de I+D+I, CTM 2010-16053).
- Niche partitioning
- Ecogeographic variables
- Classification trees