Terrestrial Palaeoecology and Global Change

Chapter 8. Ecosystem evolution
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ary: Krassilov, 1979 and elsewhere). It will be sufficient to remind, not going into detail,
that a long-distance stratigraphic correlation is based on the simultaneous over the range
replacements of widespread species. Such speciation events are definitely not in favour
of the common believes in geographic disjunction and the founder effect, but rather
indicate a diffuse, over the range, speciation processes.
A plausibility of duffuse speciation is justified, first, by compelling evidence of adaptive
genetic differentiation in spite of a considerable gene flow (Endler, 1973; Nevo et
al., 1984, 1997; Galen et al., 1991; McKay & Latta, 2002). A correlation of genetic
changes with microenvironmental differentiation has been recently convincingly demonstrated
by the ecogenetic studies over heterogenous landscapes – the “evolutionary canyons”
(Li et al., 2000a, 2000b; Belyaev et al., 2001).
Predictably, the differentiation is related to the coarse-grain adaptive strategy in respect
to environmental heterogeneity. However, the grain strategy is a consequence of
selective environment to be changed with it. A switch to the fine-grain strategy would
sweep out the pattern of the down-to-grain diversity. The heterozygosity would increase
by mixing of the ecotypic gene pools, with an appreciable effect on polygenic traits
(McKay & Latta, 2002). Genetic introgression would result in a generalist species, homogeneous
over its geographical range, with individual variation masking interpopulation
differences, as in the Early Palaeocene Trochodendroides arctica (IX.9.3).
The underlying genetic processes are as yet not fully understood but their (long denied)
correlation with ecosystem events has become more apparent recently. Thus, genetic
polymorphism fluctuates with cyclic environmental changes (Scheiner & Goodnight,
1984; Kirzhner et al., 1995; Korol et al., 1995, 1996). Stressfull environments tend
to enhance mutation rates (Wills, 1984; Parsons, 1992), partly owing to an effect on the
recombination system (Zuchenko & Korol, 1985; Cullis, 1990; Korol, 1999). In plants,
the cytoplasmic genomes are transmitted via seed flows that in the colonizing species
typically prevail over pollen flows (Ennos, 1994; Oddou-Muratorio et al., 2001). Here
the genetic transmission through cytoplasmic genomes directly dependent on the environmental
grain strategy.
Insulation of gene pools from intrusion of alien genetic material is important for the
coarse-grained populations of stable biotic communities. Yet at a non-coherent stage of
ecosystem build-up, the pioneer (disaster) populations may benefit from enrichment of
their gene pools by genetic introgression as well as by non-sexual (horizontal) transduction
of genetic material as a source of additional genetic variability.
We arrive at a model of cyclic splitting – fusion dynamics related to the alternative
population strategies in respect to environmental fluctuations. Speciation is preceded by
adaptive differentiation down to environmental grain resulting in a pattern of distinct ecotypes
that increase genetic variability over the species range. Morphological distinctions arise
through subtle developmental anabolies inflicted by the adaptive adjustments. This stage
involves the coarse-grain strategists that with a change of selective environment give way
to the fine-grain strategists bringing with them a mixing and genetic introgression over the