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CAS Workshop on Ecosystem Succession Theory and Practice of Ecological Restoration Large-scale patterns and processes of
biogeography and biodiversity of vascular plants in eastern Asia and
North America Qian Hong (Research
and Collections Center, Illinois State Museum, 1011 East Ash Street,
Springfield, IL 62703, USA) Abstract:
One of the most intriguing patterns in biogeography is the
close relationship between the temperate floras of eastern Asia and
eastern North America. This
biogeographic pattern has fascinated and intrigued botanists,
biogeographers, and ecologists for about 150 years.
Asa Gray was the first to study this pattern.
He compared the floras of Japan, eastern North America, and
western North America, and concluded that the floras of eastern Asia
and eastern North America were more similar to each other than either
was to western North America. This
conclusion attracted the attention of the world’s leading biologists
of the 19th century including Charles Darwin.
However, because the rich flora of temperate and subtropical
China was neither included in Gray’s comparison nor included in
subsequent comparisons by others, the generality of the biogeographic
pattern discovered by Gray has not been tested until recently.
We reexamined the floristic relationships based on genera
shared among eastern Asia, eastern North America, and western North
America at different spatial scales for different phylogenetic groups
using complete floras. Floristic
similarity between eastern Asia and eastern North America is higher
than that between eastern Asia and western North America, and the
floras of the eastern and western parts of North America are more
closely related to each other than are the floras of eastern Asia and
eastern North America. Compared
to eastern and western North America, the number of genera common to
eastern Asia and eastern North America is significantly higher in
basal angiosperms and significantly lower in asterids.
Floristic similarities tend to decrease from more basal to more
modern lineages between eastern Asia and eastern North America and
between eastern Asia and western North America, but not between the
eastern and western parts of North America.
Similarly, from more basal to more modern divisions, the
fraction of shared genera decreases between eastern Asia and eastern
North America and between eastern Asia and western North America
whereas the floristic similarity between the eastern and western parts
of North America tends to increase.
Furthermore, floristic similarity between eastern Asia and
eastern North America increases with latitude. Because of the close floristic
relationships between the eastern temperate parts of Asia and North
America and because of the convenient similarities in land area,
latitude range and habitat diversity in the two continents, ecologists
have recently become interested in comparisons of species diversity
between eastern Asia and North America.
Because biota and their respective continents cannot be
replicated, the comparisons of large-scale patterns in species
diversity between ecologically similar and geographically comparable
regions such as eastern Asia and North America can provide insights
into the processes and mechanisms of global biological
diversification. To
improve our understanding of patterns and underlying processes of
species diversity of vascular plants in eastern Asia and North
America, we conducted a series of comparisons at different scales
ranging from continental to local between the two continents.
At a continental scale, we compared the species diversity of
vascular plants in North America north of Mexico (19.7 × 106
km2) with that in eastern Asia north of c. 30º N latitude
(also 19.7 × 106 km2). Eastern Asia has 1.3 and 1.5 times as many genera and
species, respectively, as North America.
At a semicontinental scale, we compared the species diversity
of vascular plants in the southern parts of eastern Asia and North
America (12.4 × 106 and
12.3 × 106 km2
in area, respectively), and compared the species diversity of vascular
plants in the northern parts of eastern Asia and North America (7.3 ×
106 and 7.4 × 106
km2 in area, respectively).
The northern part of eastern Asia has 1.1 and 0.94 times as
many species and genera, respectively, as the northern part of North
America. This pattern
indicates that the diversity bias between the two continental regions
primarily results from the southern flora of eastern Asia. The diversity differences between eastern Asia and North
America are not homogenously distributed across different plant
groups. At the species
level, eastern Asia had significantly more species than expected in
magnoliids, alismatids, Liliidae, ranunculids, and rosids and had
significantly less species in the Commelinidae, Caryophyllidae, and
euasterids than North America. At smaller scales ranging from
10 to 4.7 — 106 km2, the southeastern part of
eastern Asia has, on average, more species and genera than
southeastern North America within a similar-sized area at the same
actual evapotranspiration (AET), which is considered one of the major
factors influencing the species diversity pattern.
Differences in species diversity between the two regions
increase with increasing area and AET.
The two regions converge in species diversity towards low AET,
corresponding to more northerly latitudes. In addition, we compared the
species diversity of the 57 eastern Asian-eastern North American
disjunct genera of vascular plants.
Because clades of each genus of the disjunctions in the two
regions have a sister relationship, consistent differences in species
diversity can be related to unique aspects of history or ecology of
each region. Eastern Asia
has 2.9 times as many species as eastern North America (576 versus
196) in these 57 disjunct genera.
This species diversity bias pattern in favor of Asia is in
agreement with the species diversity patterns discussed above.
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