The role of interference versus exploitative competition in shaping life histories of the smaller tea tortrix
Intraspecific competition is ubiquitous in nature and can fundamentally shape the individual life history. Competition occurs, and consequently influences life-history traits, through the direct effects of interference and indirect effects of exploitation. Importantly, it is the relative contribution of these two pathways that determines the overall impact of competition on life history. Since life history scales up to explain population dynamics, understanding the competitive mechanisms is required when predicting the impact of intraspecific competition on dynamics. However, current methods to identify the relative importance of each pathway are exclusive to a few taxa which limits our understanding of the consequences of competition. In this thesis, I designed an approach to disentangling the role of interference versus exploitation in shaping life-history traits. The approach complements lab experiments and mathematical modeling that are applicable to a broad range of taxa. I demonstrated the approach with the smaller tea tortrix (Adoxophyes honmai), a pest moth for which competition is suggested to govern its recurrent population cycles in the field and in the lab. I found that competition in the moth is best characterized by a high level of interference that results in mortality, suggesting aggressive interactions. Next, I investigated whether temperature changes competition. Using the same approach across a temperature range, I found that temperature has no major effect on the competitive mechanisms. Then, to understand why the moth competes aggressively, I explored its cannibalistic behavior. Using a lab experiment, I showed that individuals tend to cannibalize at a low rate which improves their fitness. Finally, I asked whether insecticides alter the interference competition. Using lab experiments, I found that aggressive interactions increase with sublethal doses of insecticide. Overall, I showed how competition shapes the moth life history and how this can change with environmental factors. These findings are essential for the proper embedding of competition into population models to accurately predict the pest cycles. They also imply that insecticides, by altering competition, can have substantial effects on dynamics. Lastly, the approach I developed to characterize the competitive mechanisms can help other biological systems to predict the impact of competition on population dynamics.