Trade-offs and spatial life-history strategies in classical metapopulations

The metapopulation concept dichotomizes space into the local scale of an ephemeral patch and the broader scale of the persistent multipatch system. Here, we consider how the "best" (i.e., optimal or noninvasible) life history of asexually reproducing organisms might address this dichotomy along environmental gradients via shifts in two key trade-offs. The expansion-survival trade-off expresses the relation between the combined growth and propagule production rate and the mortality rate. The accumulation-export trade-off partitions expansion into a local accumulation of growth plus propagules retained within the patch and the potential-colonist propagules dispersed to other patches, although the dispersal linkages among patches are assumed to be weak (a characteristic of "classical" metapopulations). We identify the best life histories along gradients of productivity, stress, and patch extinction rates for a metapopulation with and without lottery or overgrowth competition, and we compare them with results for an isolated immortal patch. The two trade-offs interact in determining best life histories, but this effect is generally small, supporting the validity of studies addressing the trade-offs separately. The accumulation-export trade-off responds strongly to the three gradients, increasing export with productivity and with patch extinction rate when this rate is high but decreasing export with higher stress; the expansion-survival trade-off increases expansion with productivity but fails to respond to stress and patch extinction rate gradients, except when the other trade-off does not occur. By linking the trade-offs to life-history strategies (i.e., colonization, exploitation, and tolerance), we separate strategies from phenomenology (i.e., from export, accumulation, and survival) along the gradients.