How an insect converts time into space: Temporal niches aid coexistence via modifying the amount of habitat available for reproduction

Explaining coexistence via temporal niches is challenging. One possibility is that asymmetric dispersal makes timing differences translate into spatial differences. The marine midge Clunio marinus reproduces at specific lunar phases and lays eggs when the intertidal zone is maximally exposed by the tides. In Roscoff (France) sympatric timing strains emerge at full moon (FM strain) or new moon (NM strain). However, the NM strain is a time-shifted emerger, laying eggs when the water level is higher than during FM strain emergence. Based on field samples, we show that this shift partially segregates larvae according to elevation. Modelling the dynamics within elevational zones shows that the temporal shift matters; if strains only differed in the temporal niche used for reproduction, in a manner that led to no elevational separation of the larval habitat, coexistence would remain impossible. Spatial separation is necessary and sufficient for the stable coexistence of sympatric timing strains.