Document: LOU-3-54-12

Inter- and intraspecific differences in aggressiveness among colonies of Azteca ants contribute to variation in diversity and impact of herbivores on Cecropia trees .

LAPIERRE, L.M.*

University of California, Los Angeles, CA 90095-1606 USA ¹

Abstract:
In a Costa Rican caribbean lowland rainforest, the majority of Cecropia insignis and C. obtusifolia (Cecropiaceae) individuals ultimately support a single colony of one of four Cecropia-obligate species of Azteca ants. These four Azteca species can be grouped into two behavioral response categories based on how they react to animal-caused disturbance of the host plant. Hence, two of the four species, A. constructor and A. xanthachroa, can be placed in the "aggressive" category and the other two, A. alfari and A. ovaticeps, in the "timid" category. I measured the variation in the defensive response among conspecific and congeneric colonies of Azteca and compared the diversity and impact of the insect-herbivore community feeding on mature Cecropia trees in the presence of these colonies. I have determined that in addition to there being a significant difference in behavioral response between the "aggressive" and "timid" Azteca groups, there also exists, among conspecific colonies, behavioral differences such that there are aggressive "timid" colonies and timid "aggressive" colonies. Overall, herbivore diversity and impact decrease as ant colony aggression increases. This intraspecific variation in aggressiveness among ant colonies may help explain why "timid" Azteca species, considered to be poor defenders of their host plant, persist as players in this ant-plant mutualism over evolutionary time. Previous studies have focused on interactions between Azteca ants and herbivore damage on saplings, but not on herbivore diversity or on interactions involving mature trees.

Keywords: Azteca, Cecropia, Costa Rica, ant-plant interactions

This abstract is being presented at: 3:30 PM in session:
PLANT-ANIMAL INTERACTIONS