An analysis of homogenization and differentiation of Canadian freshwater fish faunas with an emphasis on British Columbia

نویسنده

  • Eric B. Taylor
چکیده

Faunal homogenization and differentiation occur when geographic regions show increased or decreased, respectively, similarity to each other in species composition owing to introductions and extinctions or extirpations. I used species presence–absence data for “native” (i.e., estimated species compositions before European settlement) and “total” (i.e., including nonnative fishes and extinctions) faunas to examine faunal similarity of freshwater fishes among aquatic ecoregions of British Columbia and among Canadian provinces and territories. British Columbia ecoregions showed faunal differentiation as the mean Jaccard’s faunal similarity coefficient for total faunas was significantly less than that for native faunas (31.4% versus 34.9%), but some ecoregions showed homogenization (e.g., Vancouver Island and Columbia River ecoregions). Comparisons across Canada showed low but significant homogenization; average pairwise Jaccard’s coefficient was higher in total versus native faunas (29.1% similarity versus 27.8%, respectively). British Columbia’s fish fauna increased the most in similarity to other areas (except the three territories), with an average increase of 4.9%. Native faunal similarity patterns are part of Canada’s natural heritage but are threatened by humanmediated increases in nonnative species and extinctions. This analysis provides a baseline to track changes in interregional faunal relationships at different geographic scales. Résumé : L’homogénéisation et la différentiation de la faune se produisent lorsque des régions géographiques présentent des compositions spécifiques respectivement plus semblables ou moins similaires à cause d’introductions ou d’extinctions ou extirpations. Des données de présence–absence sur les faunes « indigènes » (i.e., les compositions spécifiques estimées d’avant l’arrivée des européens) et « totales » (i.e., incluant les espèces introduites et les espèces disparues) m’ont permis de comparer la ressemblance des faunes de poissons d’eau douce dans les écorégions aquatiques de Colombie-Britannique et dans les provinces et territoires canadiens. Il y a de la différentiation faunique parmi les écorégions de la Colombie-Britannique puisque le coefficient de similarité de Jaccard moyen de la faune totale est significativement moins élevé que celui de la faune indigène (31,4 % par rapport à 34,9 %), mais quelques écorégions présentent une homogénéisation (e.g., les écorégions de l’île de Vancouver et du fleuve Columbia). Les comparaisons à l’échelle du Canada indiquent une homogénéisation faible, mais significative, et les coefficients de Jaccard moyens appliqués deux à deux sont plus élevés pour la faune totale que pour la faune indigène (une similarité de 29,1 % par rapport à 27,8 %). Par comparaison aux autres régions, mais à l’exception des trois territoires, c’est en ColombieBritannique que la similarité de la faune de poissons a augmenté le plus, en moyenne de 4,9 %. Les patterns de similarité faunique indigène font partie de l’héritage naturel du Canada, mais ils sont menacés par des augmentations du nombre d’espèces non indigènes et des extinctions causées par les humains. Cette analyse fournit une base pour l’observation des changements dans les relations fauniques inter-régionales à différentes échelles géographiques. [Traduit par la Rédaction] Taylor 79

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تاریخ انتشار 2004