Ecological Impacts of a Trait-Mediated Cascade.

Abstract

Ecologists have generally recognized that trait-mediated indirect interactions (TMIIs) can have important impacts on populations and communities. What is less understood is how and to what degree the interplay of TMIIs would affect community dynamics. In this dissertation I take the study of TMIIs one step further to examine a specific system in which two interacting TMIIs act in concert, significantly regulating consumer-resource dynamics in the system. This system contains two interacting TMIIs. The first one consists of a classic ant-hemipteran mutualism. The aggressive arboreal ant, Azteca sericeasur, through its aggressive behavior and harassment prevents the coccinellid beetle, Azya orbigera, from preying on the hemipteran Coccus viridis. The second TMII occurs when the phorid fly, Pseudacteon lascinosous, a parasitoid of A. sericeasur, induces anti-parasitism behavior of the ant. Since the phorid fly needs movement to attack the ant, the ant adopts a motionless posture when the phorid is present, effectively cancelling the first TMII. This ecological system is found in the coffee agroecosystem of the Neotropics and has important implications for pest management. Through a literature review, field surveys, and laboratory experiments I document the effects of these interacting TMIIs on the coccinellid beetle, an important predator of scale insects in coffee. More specifically, my study suggests that the effects of a remote species that never directly interacts with organisms on lateral food chains can significantly affect several demographic parameters of the coccinellid beetle. It influences oviposition, parasitism and sex ratio, each of which is critical to population dynamics. The study also documents the effect of the interacting TMIIs on the general arthropod community that uses coffee. My study also suggests that the specific TMIIs interactions can have a broad community-wide impact.