  Plant-pollinator associations are often seen as purely mutualistic, while in
reality they can be more complex. Indeed they may also display a diverse array
of antagonistic interactions, such as competition and victim--exploiter
interactions. In some cases mutualistic and antagonistic interactions are
carried-out by the same species but at different life-stages. As a consequence,
population structure affects the balance of inter-specific associations, a
topic that is receiving increased attention. In this paper, we developed a
model that captures the basic features of the interaction between a flowering
plant and an insect with a larval stage that feeds on the plant's vegetative
tissues (e.g. leaves) and an adult pollinator stage. Our model is able to
display a rich set of dynamics, the most remarkable of which involves
victim--exploiter oscillations that allow plants to attain abundances above
their carrying capacities, and the periodic alternation between states
dominated by mutualism or antagonism. Our study indicates that changes in the
insect's life cycle can modify the balance between mutualism and antagonism,
causing important qualitative changes in the interaction dynamics. These
changes in the life cycle could be caused by a variety of external drivers,
such as temperature, plant nutrients, pesticides and changes in the diet of
adult pollinators.
  Abstract Keywords: mutualism, pollination, herbivory, insects,
stage-structure, oscillations
