PARENT SESSION
Oral Session #86: Invasive species: Ants and other invertebrates.
Presiding: J. Morrison
Thursday, August 8. 1:00 PM to 3:45 PM. Greenlee Meeting Room, TCC.

Does size matter? Invasive Argentine ants and the breakdown of seed dispersal mutualisms in California.

Carney, Shanna^*,1, Byerley, M.¹, Farrar, John¹, Holway, David², ¹ Colorado State University, Fort Collins, CO² University of California, San Diego, La Jolla, CA

ABSTRACT- Invasive Argentine ants (Linepithema humile) displace many native arthropods, including ants that can act as dispersers of plant seeds. The loss of these dispersal mutualists may adversely affect plant fitness if the invasive ant species does not or cannot perform the role of disperser. The fitness consequences will be exacerbated in regions where predation of undispersed seeds is common. Here we describe studies carried out over the past two years that examine the degree of dispersal of large and small seeds by native and Argentine ants and predation in the absence of dispersal. Large Dendromecon rigida (tree poppy) seeds are not dispersed by Argentine ants, presumably because of their large size relative to the size of the ants, suggesting that fitness of this myrmecochore may be reduced in the presence of the invader. Smaller seeds may not be affected as adversely since Argentine ants do collect Claytonia perfoliata (miner's lettuce) seeds. However, the fate of these seeds remains unknown. Levels of seed predation by granivores varied across sites and seed types, but it may be an important source of seed loss in the absence of dispersal.

KEY WORDS: Argentine ant, myrmecochory, seed dispersal, invasion