Chapter 10 Realms, Regions, and Provinces

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Chapter 10Realms, Regions, and Provinces
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A species, genera, or family that is resiricted
to one or a few geographic regions is endemic to
those regions. If widely distributed, they are
cosmopolitan. Quantitative estimates of floral
and/or faunal similarities between regions can be
determined using coefficients of similarity. The
following indices are common Jaccard C /
(N1 N2 C) Simpson C/N1 Where C is the
number (of families, genera, or species,
depending on the scale of analysis) common to
both regions, and N1 and N2 are the total counts
for each region. Generally, the higher the
taxonomic order being examined, the higher the
similarity across regions.
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Biogeographic provincialism the tendency for
different regions to possess unique species,
genera, or families. To the extent that this
occurs, the Earth can be subdivided into
biogeographic (rather than climatic or biomic)
regions.
Faunal regions
Floral regions
Combined regions
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Several of the proposed biogeographic lines that
separate the Australasian and Oriental regions.
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Evolution of the mammals
The first mammals appeared at about the same time
as the first dinosaurs, during the Triassic about
220 million years ago. The classic explanation
for the evolutionary development of mammals at
the KT extinction event (extraterrestrial impact
at the close of the Cretaceous) is that strong
adaptive radiation occurred to fill the niches
left vacant by dinosaur extinction. However,
many of the orders of mammal had already begun
divergence much earlier. The earliest marsupials
may have evolved in North America in the Middle
to Late Cretaceous. Today, they dominate only in
Australia (only Dipelphis (e.g., opossum) is
still found in N.A. The placentals appear to
have evolved in northern Asia shortly after the
marsupials.
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Late Cretaceous and Early Tertiary dispersal of
marsupial and placental mammals.
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Evolution of the flowering plants
Mosses, pines, and firs dominated the Earth for
300 million years until flowering plants became
prevalentbut how and when this change occurred
is a mystery.
Fossil material assigned to what might be the
first flowering plant fossil, Archaefructus
liaoningensis, originates from the Yixian
Formation in northeastern China, originally dated
as late Jurassic but now thought to be
approximately 125 million years old, or early
Cretaceous in age. Even with its revised age,
Archaefructus has been proposed to be one of the
earliest known genera of flowering plants.
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This discovery of what might be the first
flowering plant fossil, Archaefructus
liaoningensis, has led to a search for evidence
of the first flowering plants in the Hengdaun
Mountains of China, the most biodiverse temperate
forest in the world.
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The Hengduan Mountains
Largely covered in subalpine conifer forests, the
relative isolation and the fact that most of the
area remained free from glaciation during the ice
ages provides a very complex habitat with a high
degree of biological diversity.
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Amborella trichopoda is a rare understory shrub
or small tree found only on the island of New
Caledonia. It is of great interest in plant
systematics because modern molecular systematics
data place it at or near the base of the
flowering plants. That is, it represents a line
of flowering plants that very early on diverged
(about 130 million years ago) from all the other
extant species of flowering plants. Comparing
characteristics of this extant basal angiosperm,
more derived flowering plants, and the fossil
flowering plants may give us some idea of the
characteristics of early flowering plants and how
they have evolved, or changed through time.
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Late Jurassic to Cretaceous dispersal of
angiosperms (flowering plants) remains unresolved.
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• Angiosperms may possess several competitive
  advantages over other plants like gynmospores,
  ferms, and mosses
• more efficient vascular systems, better able to
  withstand drought
• Ovaries and pollen grains are often better
  protected from dessication
• Coevolution of pollen and fruit-dispersing and
  pollen-dispersing animals with the flowering
  plants produced additional mechanisms for pollen
  and seed dispersal than othe plants, which
  generally rely on the wind.
• However, gymnosperms like pine and spruce
  continued to dominate in many regions because the
  retention of needles is an advantage where
  summers are short they photosynthesize quickly
  when temperatures increase, and the loss of seeds
  to desiccation is not an issue in cooler regions.
• Finally, the hemispheric division and ocean
  barriers may have restricted the northward
  dispersal of cold-adapted angiosperms like the
  southern beech and lessened competitive pressure
  on northern gymnosperms like the pines.

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Late Cretaceous Early Tertiary distribution of
beeches and pines (all blue) and modern
distribution (dark blue).
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