The effect of an invasive alien vine, Vincetoxicum rossicum (Asclepiadaceae), on arthropod populations in Ontario old fields Crystal M. Ernst* & Naomi Cappuccino Department of Biology, Carleton University, Ottawa, ON, Canada K1S 5B6; *Author for correspondence (e-mail: cernst@connect.carleton.ca) Received 4 August 2003; accepted in revised form 11 March 2004 Key words: alien plants, arthropods, Asclepiadaceae, feeding guilds, invasive plants, Vincetoxicum rossicum Abstract Vincetoxicum rossicum is an invasive alien vine introduced from Europe in the late 1800s that is now an emerging pest in upstate New York and eastern Ontario. The plant can form dense, monotypic stands in woodlots and old fields, and may be displacing native vegetation. As a consequence, V. rossicum may be displacing arthropod fauna associated with native vegetation. In June and August 2002, we sampled V. rossicum and three other old field plants (Asclepias syriaca, Solidago altissima, and mixed graminoids) for arthropods using pitfall traps and by sampling individual plants. A total of 7868 arthropods were counted on plants and 18,195 individuals were trapped; these were sorted by feeding guild. Overall, stands of V. rossicum supported the lowest abundance of both stem- and ground-dwelling individuals, as well as the lowest number of arthropods in most phytophagous guilds. Some feeding guilds are entirely absent: V. rossicum stands are completely devoid of gall-makers and miners, and support few pollina- tors. This study suggests that arthropod diversity will decline if V. rossicum displaces native old-field plants. Introduction Although invasive alien plants have been impli- cated in major ecological changes in a variety of environments (Mack 2000), their impact has pro- ven difficult to define and measure (Parker et al. 1999). The visual impact of a monoculture of an alien plant can be striking, and it is often inferred that the plant is occupying space that would otherwise be covered by native vegetation. The effect of an alien plant monoculture on the native arthropod fauna is less obvious. Alien plants are unlikely to represent a palatable food source for most native herbivores, unless the alien is closely related to native plant species, or chemically simi- lar to them. This, in turn, has implications for in- sectivores such as breeding birds and certain small mammals. Plants generally have fewer ene- mies in their introduced range than in their native range (Wolfe 2002; Mitchell and Power 2003). However, to assess the impact of an alien plant on the food resources of native insectivores, the relevant contrast is between the fauna associated with the alien plant and that associated with native plants that may have been displaced by the alien. To date, there are few studies comparing arthropods associated with native and alien plants (but notable exceptions include Toft et al. (2001), Agrawal and Kotanen (2003) and a few studies reviewed by Keane and Crawley (2002)). Most studies on the impact of alien species usually consider the effect on a single population of a native species. Those that consider commu- nity-level impacts generally focus on species rich- ness as the response variable, even though other community metrics might be more informative Biological Invasions (2005) 7: 417–425 Ó Springer 2005