Geography Reference
In-Depth Information
Figure 5.17
Biogeographic analysis of the Gondwanan areas by Sanmartín and Ronquist
(2004). (a-f) Area cladograms representing the biogeographic patterns discussed: (a)
southern Gondwana pattern; (b) plant southern pattern; (c) inverted southern pattern; (d)
northernGondwanapattern;(e)tropicalGondwanapattern;(f)trans-Americanpattern;(g-j)
general area cladograms obtained: (g) animal data set; (h) insects excluding Eucnemidae;
(i) noninsect animals; (j) plants.
The authors then compared all taxon-area cladograms with each of the six
biogeographic patterns initially identified. They found that the animal data set was
dominated by the southern Gondwana and northern Gondwana patterns, although
the latter was almost exclusively due to the Eucnemidae. The majority of the plant
groups supported either the plant southern pattern or the inverted southern pat-
tern. Several groups did not support any clear pattern or supported a pattern dif-
ferent from those analyzed. When the phylogenies of the different taxa were fitted
to a geological area cladogram depicting the relationships of the Gondwanan land-
masses, a significant distribution pattern (
p
< .01) was displayed. However, the
processes involved differed between plants and animals. The animal data set as a
whole showed a higher frequency of vicariance, extinction, and duplication events
than expected by chance, whereas dispersal events were rare. The plant data set
also exhibited a higher frequency of duplications and a lower frequency of dis-
persals than expected, but the frequencies of vicariance and extinction events did
not depart significantly from expected values. This difference was also observed
when individual groups were fitted to the geological area cladogram. With the ex-
ception of the family Strelitziaceae, none of the plant groups showed a significant
frequency of vicariance or extinction, whereas many of the animal taxa did.
Finally, the authors examined the role played by dispersal in shaping the stud-
ied patterns by fitting the taxonomic phylogenies to the geological area cladogram.
They found that the frequency of terminal dispersals was significantly higher in
plants than in animals, but the frequencies of ancestral and total dispersals, al-
though higher in plants, did not differ from expected values. Thus, there was more
dispersal in the plant data set, but it appeared to be solely due to dispersal with-
in the widespread species. Several concordant dispersal patterns were inferred,
but they were different in animals and plants. In animals, trans-Antarctic dispers-
al between Australia and southern South America was significantly more frequent
than any of the other dispersal events involving the austral landmasses. In con-
trast, for plants, trans-Tasman dispersal (New Zealand-Australia) was significantly
more frequent than trans-Antarctic (Australia-southern South America) and trans-
Pacific (New Zealand-southern South America) dispersals. Trans-American dis-
persal (northern South America-southern South America) in animal taxa was sig-
nificantly lower than the biotic exchange between northern South America and
North America (Holarctic). Dispersal between Madagascar and Africa was signific-
antly more frequent than trans-Atlantic dispersal (northern South America-Africa).
