Terrestrial Palaeoecology and Global Change

Chapter 8. Ecosystem evolution
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Quantum steps in the process are owing to the sequential appearances of nichegenerating
forms that enhance the diversity of their co-evolving organisms by the multiple
co-adaptation ties. As a rule, the chronologically later appearing dominant forms,
such as angiosperms, are superior to their predecessors (gymnosperms) in the capability
of stabilizing their physical environments (e.g., soil conditions in hardwood forests comparative
with those in conifer forests: Lewis, 1986) and creating new ecological niches
up the trophic cascades as well as collaterally (for the rhizospheric symbionts, epiphytes,
herbivores, pollinators, etc.).
With the early land plants advancing from prostrate to erect habits, their co-evolving
fungal and animal life was elevated above the ground (as attested by the epiphytic fungi
and by arthropod feeding on sporangia: Edwards et al., 1995). More of such niches were
added by the later appearing arboreal plants generating a rich above–ground diversity.
Eventually, in the multistratal forests, canopy life has become more diverse than ground
life. Human ancestry belongs to the canopy life. Hence the origins of humanity are
owing to the early land plants that raised their sporangia above the ground and furthermore
to the flowering plants that provided for the frugivorous habits.
In this example, the diversification drive spreads upward both spatially and in terms
of trophic cascades, from primary producers to the climbing vertebrates on top. Simultaneously,
the diversification of flowering plants is driven top down by the anthophilic
arthropods and vertebrates. In both cases, a build-up of diversity is accelerated by the
positive feedbacks in the plant → herbivore → plant circuits.
At all evolutionary levels, structural complexity increases with positive feedbacks that
increase with evolutionary progress and over developmental sequences (cyanophytes excrete
substances that suppress their own growth while mammals sustain their habitats, as
in the grazer/grassland example; over an ecological succession, the pioneer species undermine
their own existence making their habitats more suitable for subsequent seral stages;
even the modern human technologies tend to advance from devastating to sustainable).
Co-adaptation pertains to the ability of interaction with a positive feedback, whereas maladaptive
forms generate negative feedbacks of an adverse effect on biological diversity.
A species entry either decreases the pre-existing diversity by competitive elimination of
resident species or inflames diversification by opening niches for further entries. Since
ecosystem efficiency correlates with diversity, the progressive evolutionary trend is associated
with the niche creating entries alone. In other words, the evolution of ecosystems (as
well as human social systems) is owing to those organisms (human individuals) that create
new ecological niches rather than those that compete for the established ones.
VIII.3.6. Diversity and niche overlap
A build-up of biological diversity associates with diversification of habitats (Benton,
2001), a trend that is taken for granted in evolutionary studies, but is actually a function