3 The New York Years (1931–1953)

Zoogeography 169
and Colombia was closed. The number of recent South American elements is much
smaller in the arid habitats of Central America than in the tropical rainforest which
was massively invaded by South American species. Therefore, the arid habitats of
Central America reflect the composition of the Tertiary North American bird fauna
more accurately than the humid tropical habitats.
The North American continent was connected with Europe (via Greenland)
in the early Tertiary and has had intermittent connections with Asia across the
Bering Strait bridge (Mayr 1964c). It was separated from South America by several
water gaps and its fauna evolved in isolation during the first half of the Tertiary,
when the southern half north to 38–40° latitude was humid and tropical (“tropical
North America”). Indigenous North American bird families which here evolved
include the wrens (Troglodytidae), mockingbirds (Mimidae), vireos (Vireonidae),
wood-warblers (Parulidae) and buntings or American sparrows (Emberizidae).
In an article on the “Age of the distribution pattern of the gene arrangements
in Drosophila pseudoobscura” Mayr (1945i) discussed the long-distance dispersal
ability of these flies which occur in western North America and Middle America.
They may be assumed to have jumped across the lowlands of the Isthmus of
Tehuantepec in Mexico by aerial transport in fairly recent geological time. It is not
so much the factor of transport that matters, but rather the ability to get established
andtosurvivebecauseofcompetitionandotherecologicalfactors.Acluetothe
possibly rather early origin of the gene arrangements (as opposed to their current
distribution patterns) is that they are found both in Drosophila pseudoobscura and
D. persimilis and may have been present already in the ancestor of these species
during the late Tertiary.
Mayr (1964c,s) discussed the Neotropical Region and its bird fauna and analyzed,
with W.H. Phelps, Jr., the avifauna of the impressive table mountains (tepuis)
of southern Venezuela and the border region of Brazil and Guyana which they
named collectively Pantepui (Mayr and Phelps 1955f, 1967c). 96 bird species are
subtropical elements of this region’s montane avifauna (of which 29 are endemic).
Among the 48 species of long-distance colonists at least 24 presumably came from
the Andes to the west, 19 from the coastal cordilleras of northern Venezuela, and
five from more distant areas. In this Pantepui region there is a completely even
gradation from endemic genera to species that have not even begun to develop
endemic subspecies. Fewer than one third (29 species) of the subtropical bird fauna
are endemic species. These facts provide conclusive evidence for the continuity
and long duration of the colonization of the Tepui Mountains, which have been
open to colonization for millions of years. Many of the older endemics probably are
extinct and have been replaced by younger immigrants during a process of faunal
turnover. In contrast to the bird fauna, the flora of Pantepui shows relationships
primarily with that of the highlands of southeastern Brazil or even with Africa.
Only 11 percent of the 459 plant genera known from the summit of Pantepui are related
to Andean plant genera (Steyermarck 1979). What characterizes all local bird
faunas is their composite nature. They are composed of colonists from different
source areas.