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Population dynamics and regeneration of a hybrid zone between Eucalyptus risdonii Hook. f. and E. amygdalina Labill.

Potts, BM 1986 , 'Population dynamics and regeneration of a hybrid zone between Eucalyptus risdonii Hook. f. and E. amygdalina Labill.' , Australian Journal of Botany, vol. 34, no. 3 , pp. 305-329 , doi:

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Regeneration of a hybrid zone between E. amygdalina and E. risdonii and pure species stands following wildfire is reported, as well as the reproductive and vegetative fitness of parental and hybrid phenotypes. E. risdonii phenotypes dominated the seed rain and seedling cohort and there was clearly a marked fitness differential between E. amygdalina and E. risdonii at their boundary. When the FI type hybrid is in competition with both parental types it is generally reproductively the least fit, although frequently vegetatively vigorous. Reduced fitness appears to extend to advanced generations as hybrid phenotypes tending.toward either species are, on average, less fit than the corresponding parental type. The pattern of phenotypic fitness suggests that the species' boundary is in disequilibrium and it is argued that E. risdonii is invading the range of E. amygdalina by both pollen and seed migration. There is an asymmetric distribution of F1 type hybrids across the boundary and the hybrid swarm examined is being invaded by E. risdonii genes. It is suggested that hybridization may be associated with natural disequilibrium and, where seed migration is limited, boundary movements may be preceded by a wave of hybridization due partly to pollen swamping of the least fit species. Hybrid swarms may develop but, at the boundary of large stands, are probably transitory. There is a marked inertia in the population response to the prevailing selective regime due to the extremely slow population turnover and limited dispersal potential. This is discussed in the broader context of non-equilibrium models where it is argued that dispersal may be the factor limiting population response to perturbation of a shallow environmental gradient. This is due to large geographical shifts in the position of the null point and would be accen- tuated in a patchy environment where migration as a front is prevented.

Item Type: Article
Authors/Creators:Potts, BM
Journal or Publication Title: Australian Journal of Botany
ISSN: 0067-1924
DOI / ID Number:
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BM Potts. Copyright © 1986 CSIRO

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