Fig. 1.

Spatio-temporally structured environments. a A rocky shore exposed to tidal cycles represents an example for structured environments considered in this article. Nutrients are replenished and contents of all small tidal pools are mixed during high tide, while allowing for segregated growth during low tide. The picture is taken by the authors and shows the coastline of Haifa (Israel) near Tel Shikmona. b Schematic depiction of cycles of growth, mixing and reseeding. Our model of many microbial populations growing in compartmentalized demes can be described by multilevel selection. Two levels are given by the growth dynamics within demes, and the cyclic dynamics of mixing and reseeding on a longer time-scale