Abstract
Temporal niches do not automatically promote coexistence. We combine field data on the marine midge Clunio marinus with a model. In Roscoff (Brittany, France) sympatric C. marinus timing strains emerge at full moon (FM strain) or just before new moon (NM strain). We show that NM individuals reproduce and lay eggs when the water level is higher than during FM strain reproduction, and that this shift partially segregates larvae according to elevation. Modelling the underlying dynamics shows that the causality from temporal to spatial niches is crucial for coexistence: for hypothetical strains which differ in the temporal niche used for reproduction so that they use equivalently low water levels for egg-laying, the dynamics show priority effects, not coexistence. While general theory on temporal niches is rather complex, we highlight the understudied possibility that timing traits cause differences in space use, and coexistence is unproblematic as it results from spatial niches.