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The effects of urbanization on ant assemblages (Hymenoptera: Formicidae) associated with the Molson Nature Reserve, Quebec

  • Jean-Philippe Lessard (a1) and Christopher M. Buddle (a1)

Urbanization causes the fragmentation of natural habitats into isolated patches surrounded by anthropogenic habitats. Fragment size and the intensity of human disturbance have been shown to affect both composition and diversity of arthropod communities, but most groups have been understudied. We investigated effects of urbanization on ant assemblages (Hymenoptera: Formicidae) in and around the Molson Reserve, a preserved maple-beech forest surrounded by residential properties near Montréal, Quebec. We studied how local ant assemblages differed in terms of composition, abundance, and species richness, depending on whether they were situated in the interior forest, in adjacent residential backyards, or at the edge between these two habitats. We also compared an intact forest interior with a younger and moderately disturbed forest (“buffer zone”) between the urban matrix and the interior forest. Few differences were detected between the buffer zone and the intact forest interior. Extrapolated estimates of species richness suggest that it is lowest in the forest interior and highest in urban zones. Community composition, as investigated with ordination analysis, revealed a clear difference between the fauna of urban sites and the fauna of edges and forest interiors, and analyzing the relative abundance of ants showed residential backyards to contain the most ants. Urban assemblages were characterized by several competitively dominant species, including one introduced or “tramp” species. The occurrence of aggressive and dominant species in urban sites and at the edges of the Molson Reserve could potentially interfere with the dispersal and immigration of ground-dwelling arthropods and negatively affect local diversity or community composition in isolated forest reserves in urban centres.


L'urbanisation fragmente les habitats naturels et les isole au sein d'espaces habités et modifiés par l'homme. Des études menées à l'échelle régionale suggèrent que la taille des îlots forestiers, ainsi que les perturbations humaines, affectent leur composition et la diversité des communautés d'arthropodes y habitant. Cependant, pour de nombreux autres groupes d'arthropodes ces effets n'ont pas encore été adéquatement testés. Nous avons exploré les effets de l'urbanisation sur les communautés de fourmis (Hymemoptera : Formicidae) à l'intérieur et aux alentours de réserves Molson, une érablière à hêtre adjacente à des propriétés résidentielles près de Montréal, Québec. Nous avons étudié comment l'assemblage des communautés de fourmis diffère en terme de composition et de richesse spécifique, en fonction de leur localisation, soit à l'intérieur de la forêt, de terrains résidentiels adjacents ou dans l'écotone séparant ces deux habitats. Nous avons aussi comparé le centre d'une forêt vierge avec celle d'une forêt plus jeune modérément perturbée qui tient le rôle d'un gradient plus traditionnel (« zone tampon ») entre la matrice urbaine et l'intérieur de la forêt. Bien que peu de différence ne fusse détectée entre la foret vierge et la zone tampon, l'extrapolation de la richesse spécifique suggère que l'intérieur de la forêt est dotée d'une richesse spécifique plus basse, tandis que la zone urbaine comprend une richesse spécifique plus élevé. Comparativement à l'intérieur et à la lisière des forêts, les fourmis sont plus fréquemment collectées dans les terrains résidentiels, et sont composées de plusieurs espèces dominatrices, incluant des espèces introduites ou vagabondes. L'occurrence d'espèces de fourmis agressives et dominantes dans les sites urbains et dans les lisières (écotones) de la réserve Molson pourrait potentiellement interférer avec la dispersion et l'immigration des arthropodes terrestres, et affecter négativement la diversité locale ou la composition des communautés au sein des réserves forestières isolées dans les centres urbains.

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The Canadian Entomologist
  • ISSN: 0008-347X
  • EISSN: 1918-3240
  • URL: /core/journals/canadian-entomologist
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