Regulation of the Demographic Structure in Isomorphic Biphasic Life Cycles at the Spatial Fine Scale

Isomorphic biphasic algal life cycles often occur in the environment at ploidy abundance ratios (Haploid:Diploid) differentfrom 1. Its spatial variability occurs within populations related to intertidal height and hydrodynamic stress, possiblyreflecting the niche partitioning driven by their diverging adaptation to the environment argued necessary for theirprevalence (evolutionary stability). Demographic models based in matrix algebra were developed to investigate which vitalrates may efficiently generate an H:D variability at a fine spatial resolution. It was also taken into account time variation andtype of life strategy. Ploidy dissimilarities in fecundity rates set an H:D spatial structure miss-fitting the ploidy fitness ratio.The same happened with ploidy dissimilarities in ramet growth whenever reproductive output dominated the populationdemography. Only through ploidy dissimilarities in looping rates (stasis, breakage and clonal growth) did the life cyclerespond to a spatially heterogeneous environment efficiently creating a niche partition. Marginal locations were moresensitive than central locations. Related results have been obtained experimentally and numerically for widely different lifecycles from the plant and animal kingdoms. Spore dispersal smoothed the effects of ploidy dissimilarities in fertility andenhanced the effects of ploidy dissimilarities looping rates. Ploidy dissimilarities in spore dispersal could also create thenecessary niche partition, both over the space and time dimensions, even in spatial homogeneous environments andwithout the need for conditional differentiation of the ramets. Fine scale spatial variability may be the key for the prevalenceof isomorphic biphasic life cycles, which has been neglected so far