PARENT SESSION
Contributed Oral Session 122: Invasive Species: Pollination - Dispersal
Thursday, August 11, 8:00 AM - 11:30 AM, Meeting Room 521 A, Level 5, Palais des congrès de Montréal
Multiple interactions among non-native insects affect seed set of an invasive tree.
Lach, Lori*,1, 2, Suarez, Andrew2, 1 Mauritian Wildlife Foundation, Vacoas, Mauritius2 University of Illinois--Urbanana-Champaign, Urbana, IL
ABSTRACT- To become established, introduced species must compete with resident species that have an evolutionary history with their environment. The success of an invasive species may be facilitated the presence of other invaders that can modify the abiotic and biotic environment. Synergistic interactions among non-native species may be an important component of invasion success, but until recently, have received little attention. Leucaena leucocephala, native to Central America, has been planted extensively in tropical agroforestry projects around the world, but is also considered one of the world's worst invasive species. L. leucocephala has extrafloral nectaries, which are thought to attract ants in exchange for protection from herbivores. We conducted an ant-exclusion experiment to determine whether an invasive ant from east Asia, Technomyrmex albipes, would be attracted to and benefit L. leucocephala in a novel environment for both species. T. albipes visitation to L. leucocephala trees was positively associated with the number of extrafloral nectaries, as well as the presence of scale insects. Sap-sucking psyllids (Heteropsylla cubana), also native to Central America, were the most common herbivores. Increasing visit frequency by T. albipes was associated with a lower proportion of rachi affected by psyllids but did not affect the frequency of psyllid incidence. Psyllids in the absence of ants, and ants in the absence of psyllids both had negative effects on seed set. However, the frequency of ant visits interacted with the frequency of psyllid incidence to yield a net positive effect on seed set. This positive interaction between ants and psyllids was offset when there were high frequencies of scale infestation. Thus T. albipes may be facilitating the spread of L. leucocephala when it occurs with H. cubana, but only if T. albipes is not also increasing scale infestation on the tree. Our findings illustrate the importance of interactions among non-native species in promoting their success. Moreover, mutualistic interactions among invaders can be context-dependent, and the magnitude and direction of their effects can be quite complex involving direct and indirect effects among many species.
Key words: facilitation, invasive species, Leucaena leucocephala, Technomyrmex albipes