Abstract
Isomorphic biphasic algal life cycles often occur in the environment at ploidy abundance ratios (Haploid:Diploid) different from 1. Its spatial variability occurs within populations related to intertidal height and hydrodynamic stress, possibly reflecting the niche partitioning driven by their diverging adaptation to the environment argued necessary for their prevalence (evolutionary stability). Demographic models based in matrix algebra were developed to investigate which vital rates may efficiently generate an H:D variability at a fine spatial resolution. It was also taken into account time variation and type 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 population demography. Only through ploidy dissimilarities in looping rates (stasis, breakage and clonal growth) did the life cycle respond to a spatially heterogeneous environment efficiently creating a niche partition. Marginal locations were more sensitive than central locations. Related results have been obtained experimentally and numerically for widely different life cycles from the plant and animal kingdoms. Spore dispersal smoothed the effects of ploidy dissimilarities in fertility and enhanced the effects of ploidy dissimilarities looping rates. Ploidy dissimilarities in spore dispersal could also create the necessary niche partition, both over the space and time dimensions, even in spatial homogeneous environments and without the need for conditional differentiation of the ramets. Fine scale spatial variability may be the key for the prevalence of isomorphic biphasic life cycles, which has been neglected so far.
Highlights
Algae species with isomorphic biphasic life cycles have their alternating haploid and diploid generations cohabiting
The demographic matrix was generalized for parsimony and not adjusted to any particular population or species: (i) the haploid and diploid fecundities were dependent on the parameters from the (fH) and fD and a size class weight factor accounting for allometry; (ii) the survival of the carpospores (Scarp) and of the tetraspores (Stet) was kept constant; (iii) the haploid and diploid ramet growth rates were dependent on the parameters gH and gD; (iv) the haploid and diploid stasis, breakage and clonal growth were aggregated as looping rates and dependent on the parameters lH and lD
The introduction of spore dispersal and settlement in a fine scale spatially heterogenic environment approximated the simulations from real world situations relative to previous non-dimensional modeling
Summary
Algae species with isomorphic biphasic life cycles have their alternating haploid and diploid generations cohabiting. It would be expected to find balanced abundances between ploidy phases as a consequence of isomorphicity. These often are uneven as reported in several studies [1,2,3,4,5,6,7]. Hughes and Otto [8] have mathematically proved the necessity for a niche partition for one of the ploidy phases to not exclude the other, eliminating the biphasic life cycle and fixing it as a monophasic one. In their non-spatial model solved for steady-state, the niche partition was due to conditional differentiation of the ploidy phases and led to a fixed H:D
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