Terrestrial Palaeoecology and Global Change

Chapter 8. Ecosystem evolution
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duction of leaf/xylem ratio with extinction of macrophyllous cycadophytes induced dental
innovations in the Late Cretaceous ornithopods, their posterior occlusive dentition and
toothless beaks increasing the range of palatable plant tissues (Norman & Weishampel,
1985; Wing & Tiffney, 1987). Semenivory and frugivory might have evolved in respect to
the ornithopod feeding habits that were reciprocated by endozoochorous adaptations in
plants in turn preparing the herbivore niches for the early mammals (e.g. a hard seed
gnawing in the mid-Eocene: Collinson & Hooker, 2000)
Plant–animal interactions are commonly recognized as a leading factor in the origin
of flowering plants and the build-up of their morphological and biochemical diversity.
With flowering plants, pollination ecology has become a focal point of ecosystem evolution.
Multistratal canopies of angiosperm communities have greatly enhanced animal
biodiversity while, on the other hand, certain angiosperm-dominated biomes, in particular
the grasslands, are sustained by herbivory. With the rise of flowering plants, the herbivore–vegetation
systems (such as the grazer–grassland systems) took control over plant
evolution intercepting the climate–vegetation systems.
Yet, by the appearance of flowering plants, all the essential modes of plant–arthropod–tetrapod
interactions were there, ready for the newcomers to pick up. In this way,
diversification of a new group is prearranged by the antecedent co-adaptations.
VIII.1.4. Coenotic gene pool
An as yet not fully appreciated aspect of co-evolution is related to the role of exogenous
nuclear acids, conceivable since the fundamental discovery by Gershenson (1939).
The genomes of multicellular organisms are not impenetrable to genetic material scattered
over biotic community in the form of DNA and RNA molecules stored in soil and
transduced by various microorganisms (Kordum, 1982). Recent genetic research has
revealed the ubiquity of microbial gene transduction as a powerful mutagenic factor
(Syvanen & Kado, 1998; Vorontsov, 2000). Gene pools of co-existing populations are
thereby included in the higher order, coenotic, gene pool of the biotic community.
The coenotic gene pool concept may prove useful in elucidating the origins of symbiotic
systems. Thus, plant–fungi interactions involve genetic transduction as a method
of symbiotic integration. Plants having ectomycorrhizal symbionts produce elicitors of
fungal growth that comprise chitinases of fungal cell walls (Salzer et al., 1997), a
biochemical convergence owing to a one way or possibly reciprocated flow of genetic
material.
Since physiological responses induced by symbionts are more flexible and less costly
than constitutional changes, symbiosis plays a leading role in plant evolution. Plant –
fungi symbiosis is the most ancient one, with primitive plants penetrating the mycelia and
vice versa. Certain plant – fungi interactions, in particular, with an involvement of haploid
spores and pollen grains, are fairly persistent over times (Fig. 112). The developing fun-