To breed or not to breed? Population dynamic consequences of flight-fecundity tradeoffs in lepidopteran systems

Plant–pollinator and plant–herbivore interactions are two of the most important ecological interactions that shape patterns of biodiversity and biomass across the globe. Historically these two lines of research have been independent of each other, and much of our knowledge of them has been synthesized and documented in herbivory-pollination systems with a focus on plant-perspective mechanisms. However, recent work has proposed that resource allocation tradeoffs between insect investment into flight and fecundity may be an important mechanism that links herbivory with pollination in Lepidoptera whose larvae are herbivores and adults, in general, are pollinators. While the individual physiological processes underpinning such tradeoffs in Lepidoptera are becoming more clear, our knowledge of how investment into flight versus fecundity scales up to affect population dynamics of both insects and their host plants is still very limited. To address this question, we built dynamical models to simulate population-level effects of (i) different magnitudes in flight/fecundity tradeoffs (from high to low) in male and female Lepidoptera, and (ii) different flight/fecundity tradeoff functions (from liner to non-linear) in males and females. First, our results indicate that different investment magnitudes in males and females induce qualitatively different oscillatory abundance behavior around equilibria in both plant and insect populations. Second, our results reveal a complex interaction between different investment magnitudes and non-linear tradeoff functions in both sexes, which created a mosaic of population densities. In all, our results build toward a more mechanistic and theoretical foundation in predicting patterns of herbivory and pollination between interacting species.