ALLOPATRIC AND SYMPATRIC ISOLATION
If the evolutionary model is correct, geography matters. Mountain ranges, oceans, rivers, canyons, and islands can isolate species in a unique environment. As a population adapts to a local environment, geographical barriers can separate it from parent populations. As a result, differences between the two populations can accumulate over time and foster the development of new species, new genera, and new families. Much of earth's current and past biodiversity would have been influenced by the geography of the areas where it evolved.
If the creationists model is correct, geography doesn't matter. No matter what environmental conditions existed in North America, South America, Africa, Australia, etc. originally, the ancestral members of each kind of organism were present in the Middle East only a few thousand years ago where they interacted with the first humans. Shortly afterwards, all kinds of organisms were present in the Middle East to board a large ark and, following the destruction of virtually all life on earth, all kinds of organisms disembarked off the ark in the Middle East. From there, every type of modern organism migrated to its current habitat. Thus, the first members of each group could only adapt to the habitats of the Middle East they experienced. Given that these species then somehow were able to travel from the Middle East to North America, South America, Australia, Hawaii, Madagascar, and every inch of this planet, they must have had the ability to overcome the barriers presented by oceans, mountains, rivers, etc. There is no reason to expect that the diversity of these highly mobile Middle-Eastern organisms would be determined by the local environmental conditions of any single part of the world.
The earth is a big place. A great percentage of the modern and past
biodiversity seems to have resulted from the geographic isolation of species.
Allopatric isolation is the key to speciation in many species of birds,
especially island species(Grant, 1997). In New Guinea, the Papuan kingfisher
populations of islands around New Guinea are more varied than those in
the diverse habitats of New Guinea itself (Raven, 2002). Darwins finches
include six species feed on the ground primarily on seeds (although some
have a longer bill which allows them to also feed on cactus flowers),
four species of insect-eating tree finches, one tree finch which uses
twigs as tools to probe for insects, a warbler finch which possesses a
very thin beak and preys on insects on vegetation, and a vegetarian finch
with a thick bill to pull buds from branches (Raven, 2002).
Outside the oceans, the greatest diversity of freshwater fish in the
world occur in the Neotropics, where about 8,000 species reside. Many
species are endemic to specific areas and their distribution is best explained
in light of the geological events of the Cenozoic involving the uplifts
of tectonic plates and the resulting changes in drainage basins (Hardman,
Estimates of the number of modern cichlid species vary from 1400 to 1700.
The speciation of cichlids correlates with the breakup of the former southern
continent of Gondwana and the water systems created by tectonic activity
on individual southern continents. From Africa, one lineage traveled to
South America and was the source of the monophyletic Neotropical clade
(Murray, 2001). Central American cichlids were colonized from South America
and some South American cichlids belong to the clade which colonized Mesoamerica.
One tribe (Heroini) diversified in Mesoamerica where they can compose
a quarter of fish species (Concheiro Perez, 2007; Martin, 1998; Husley,
2004). During the Miocene, tectonic uplift in East Africa changed water
drainage patterns and created the great lakes which were the centers of
cichlid diversity (Murray, 2001). Most African cihlids are thought to
have arisen from the paleo-basin of Lake Tanganyika (including the extinct
Lake palaeo-Makgadikgadi) and the greatest diversity of modern cichlids
is endemic to East Africa (Katongo, 2007). More than a thousand species
of cichlid fishes inhabit the three African Great Lakes, Tanganyika, Malawi
and Victoria (Watanabe, 2007).
Many catfish species diversified as plate tectonics changed the waterways
and the geography of the southern continents. When the Indian subcontinent
collided with Eurasia 50 to 45 million years ago, it began the formation
of the Tibetan plateau, the largest and highest plateau on Earth (5 million
square kilometers and an average height of 5 km). The resulting geologic
changes allowed for the speciation of diverse fish lineages endemic to
the area, such as the glyptosternoid catfishes (Peng, 2006). More than
50 fish species are endemic to the Maracaibo basin of northwestern Venezuela
which was formed by a rising section of the Andes 8 to 10 million years
ago (Hardman, 2006). As the Death Valley region dried, the few remaining
springs were colonized by past species that adapted to that spring. Many
fish (such as pupfish) have evolved into separate species whose distribution
may be limited to one spring only (Campbell, 2003).
Reptiles and amphibians thrive in the tropical regions of the world but
mountain ranges, rivers, and oceans often form geographic barriers that
they cannot cross. The salamander species Ensantina escholotzii is a ring
species which has produced a number of populations in different sites
around the mountains that form a barrier for it in California. These populations
vary and are in the process of becoming separate species (Campbell, 2003).
In areas of the American southwest, populations of species of lizards,
rodents, and insects that inhabit dark rock formations have darker colors
than populations which inhabit the sand of the surrounding desert (Raven,
2002). About half of all modern amphibian species inhabit tropical regions in the Western hemisphere. More than 800 species of frog are classified as eleutherodactyline frogs which undergo direct development. This group originated in South America in the early Cenozoic. Much of the subsequent speciation in South America occurred while the Andes uplift was altering habitats. Additional speciation occurred as ancestral species traveled over water to reach Central America and the West Indes (Heincke, 2007).
Many birds are endemic to specific areas. New World vultures and Old
World vultures arose from unrelated groups of ancestral birds in different
parts of the world. Virtually all suboscines occur in North and South
America and the greatest number live in the tropics. Fossil and genetic
evidence suggests that passerine birds evolved on the southern supercontinent
of Gondwana. (Slack, 2007, Edwards, 2002).
Oscine passiformes are the predominant group of birds in the Northern Hemisphere. Oscine passiform groups form a nested hierarchy of related families. Birds in related families can be quite similar to each other, such as the Old World and New World warblers.
Many mammals species evolved in isolated areas and were able to diversify and migrate after their lineage had been established (such as horses and camels from North America or elephants and hominids from Africa). Obviously, the unique marsupial fauna of Australia owes much of its diversity to the isolation from competition from placental animals. Madagascar ’s natural habitats experience extremes in precipitation levels which leads to unpredictable patterns of flowering and fruiting. Selection pressure has resulted in wildlife that have evolved ways of tolerating these extremes (Dewar, 2007).