APLICAÇÃO DE MODELOS MATRICIAIS NA MODELAÇÃO ECOLÓGICA

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What drives distinct ploidy phases of isomorphic biphasic life cycles to occur at uneven abundances

Publication . Vieira, Vasco Manuel Nobre de Carvalho da Silva; Santos, Rui

Throughout the history of eukariotic primary producers, namely the plant and algae, there was an evolution of the life cycles along with their morphological and physiological complexity and role on the ecosystems. The earlier, simpler ones, namely the bryophytes, have haploid life cycles. The most complex and evolved ones, namely the vascular plants, have diploid life cycles. In between there is a whole range of taxa with haploid-diploid life cycles. It most often occurs in brown or red algae. In the former the ploidy phases are heteromorphic whereas in the latter are frequently isomorphic, which raises the question about the reasons for their unbalanced occurrence in their habitats when these are expected to be even as a consequence of isomorphicity. The hypothesis that have been proposed may be resumed to two: (i) ploidy dissimilarities in their fecundities as a consequence of the differential cytological processes of spore production; and (ii) ploidy dissimilarities in growth and survival, of both spores and fronds, as a consequence of a conditional differentiation required to the stability and evolution of their biphasic life cycles. However, there is a gap between the hypotheses proposed and the observed pattern of phase dominance as the link has not been proved so far. The objective of the present thesis is to help filling this gap by establishing how ploidy dissimilarities in the life cycle may generate effective uneven abundances that match the observed in the field. To do that the thesis is divided into six chapters. In the first chapter there is a general introduction to the subject. In the second chapter it was accessed how different types of vital rates may be generally efficient, or inefficient, forcing functions upon the pattern of ploidy phase dominance. In the third chapter it was accessed how efficiently the different types of vital rates may impose a geographical variability of ploidy dominance like the ones reported for a few species. In the forth chapter it was accessed how the life cycle response to time instability is dependent on the ploidy dissimilarities in the vital rates, and how time variability may surge even in stable environments. In the fifth chapter it was accessed how efficiently, or inefficient, the different types of vital rates may impose an intra-population pattern of ploidy dominance with a fine resolution both over space and time, as it has been reported in the literature. In the sixth chapter are the final conclusions. It was found that ploidy phase dissimilarities upon the survival rates of the fronds and/or upon the performance of the spores are the most efficient and likeliest drives for the patterns of ploidy phase dominance observed in the field.

2011Doctoral thesis

Open access

Responses of the haploid-to-diploid ratio of isomorphic biphasic life cycles to time instability

Publication . Vieira, Vasco; Santos, Rui

Previous modelling of the haploid-to-diploid ratio (H:D) in biphasic life cycles relied on estimates of the stable population growth rate and structure. This is a projective analysis that estimates the population dynamics given current conditions. However, the environment is rarely constant and has both periodicity and random instabilities. The objective of this work was to unveil how the H:D responds to them. It was found that ploidy phase dissimilarities on the demographic matrix and/or in the initial population structure cause an inevitable H:D time variability as a consequence of the life-cycle structure and independent of the environmental seasonal cycle. This variability depends on the type of life strategy, demographic processes involved and ploidy dissimilar vital rates. Furthermore, ploidy dissimilar fertility or growth rates cause cyclic oscillations mismatching the seasonal cycle, whereas ploidy dissimilarities in the ramet looping rates (survival related) induce a monotonical variation.

2012Journal article

Open access