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Effects of gypsy moth establishment and dominance in native caterpillar communities of northern oak forests

Published online by Cambridge University Press:  07 September 2012

Laura L. Timms  and
Sandy M. Smith
Laura L. Timms*
Affiliation:
Faculty of Forestry, University of Toronto, 33 Willcocks Street, Toronto, Ontario, Canada M5S 3B3
Sandy M. Smith
Affiliation:
Faculty of Forestry, University of Toronto, 33 Willcocks Street, Toronto, Ontario, Canada M5S 3B3
*
1Corresponding author (e-mail: laura.timms@utoronto.ca).
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Abstract

Little research has addressed the impacts of invasive-species establishment on native forest insect communities. Such information is lacking even for gypsy moth, Lymantria dispar (L.) (Lepidoptera: Erebidae), the most thoroughly studied invasive forest insect. We investigated the ecological impacts of gypsy moth on native species at sites in north-central Ontario, Canada, with and without significant histories of gypsy moth defoliation over a 2-year period. Patterns in native forest caterpillar communities are described using measures of species diversity and multivariate analysis. We documented a transition from low-level to dominant gypsy moth populations. Sites with different gypsy moth outbreak histories exhibited differences in rank-abundance distributions and dominance structures in the first year of the study; by the second year, gypsy moth was dominant at sites of both types irrespective of their previous defoliation history. Contrary to our predictions, we found that gypsy moth outbreak history had no significant effects on native caterpillar community diversity or structure. However, sites with currently high gypsy moth abundance demonstrated significant shifts in late-season caterpillar community structure. Our results suggest that observed community differences were due to the presence of a highly abundant folivore, and not to permanent shifts in the native community because of the introduction of an invasive species.

Résumé

On a consacré peu de recherches aux impacts de l—établissement des espèces envahissantes sur les communautés d'insectes forestiers indigènes. Il n'existe pas d'informations de cette nature même pour la spongieuse, Lymantra dispar (L.) (Lepidoptera : Erebidae), l'espèce d'insecte forestier envahissant la mieux étudiée. Nous examinons les impacts écologiques de la spongieuse sur les espèces indigènes à des sites du centre nord de l'Ontario, Canada, avec ou sans histoire de défoliation significative par la spongieuse au cours d'une période de deux ans. Nous décrivons les patrons dans les communautés de chenilles forestières indigènes à l'aide de mesures de diversité et d'analyses multidimensionnelles. Nous avons observé une transition des populations de spongieuses de densité faible à dominante. Les sites qui ont connu des déroulements différents de l—épidémie possèdent des distributions de rangs d'abondances et des structures de dominance différentes durant la première année de l—étude; dés la seconde année, la spongieuse domine dans les deux types de sites, quelle que soit leur histoire antérieure de défoliation. Contrairement à nos prédictions, l'histoire antérieure de l—épidémie des spongieuses n'a aucun effet significatif sur la diversité ni sur la structure de la communauté de chenilles indigènes. Cependant, les sites qui ont présentement de fortes abondances de spongieuses accusent des changements significatifs de structure des communautés de chenilles de fin de saison. Nos résultats laissent croire que les différences observées dans les communautés sont dues à la présence d'un folivore extrêmement abondant et non à des changements permanents de la communauté indigène à cause de l'introduction d'une espèce envahissante.

[Traduit par la Rédaction]

Type
Research Article
Information
The Canadian Entomologist , Volume 143 , Issue 5 , September 2011 , pp. 479 - 503
Copyright
Copyright © Entomological Society of Canada 2011

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