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164 4 Ornithologist and Zoogeographer
and Wilson’s Island Biogeography (1967)” (Mayr 1976m: 616; see also Bock [1994a:
292] and Vuilleumier [2005b: 59, 65–66]).
Several dynamic zoogeographers had long ago realized that wherever there is
biota, there is input (immigration, colonization) and output (extinction, emigration):
The numerical values of MacArthur and Wilson’s theory (1967) are “mere
icing on the cake,” as Mayr (1983e: 15) later put it. The discovery of numerous
bird fossils on many Pacific islands (Steadman 2006)—unknown to Mayr and
other early workers—indicates that during prehistoric times, much richer species
communities inhabited many of these islands than currently found. Quantitative
theoriesofislandbiogeographywillhavetoberevisedonthebasisofinventories
that describe the island avifaunas before human impact.
As to continental faunas Mayr (1965q: 484) emphasized that instead of a descriptive
static definition (“A fauna is the totality of species living in an area”)
a dynamic definition is to be preferred: “A fauna consists of the kinds of animals
found in an area as a result of the history of the area and its present ecological
conditions” and “Instead of thinking of fixed regions, it is necessary to think of
fluid faunas” (1946h: 5). Aspects of faunal studies are the analysis of endemism and
of the faunal elements which differ in origin, age, and adaptation. The interest of
modern zoogeographers centers on faunas rather than regions. Faunas originated
(a) through continuous autochthonous differentiation in (at least temporary) geographical
isolation from other faunas, during which time they acquired their
special characteristics, (b) through continued single origin colonization (e.g., the
Australian bird fauna), (c) through continued multiple-origin colonization (e.g.,
the bird faunas of Hawaii, West Indies, Pantepui, Tristan da Cunha), (d) through
the fusion of two faunas (e.g., the faunas of the Malay Archipelago and of Central
America).
Mayr also pointed out that adaptive radiation is not a phenomenon restricted
to island faunas. There are examples on continents as well, e.g., the troupials
(Icteridae) of the Americas. Another problem is the varying dispersal characteristics
of individual taxa, even within a group of ecologically comparable families.
Among grassland finches, the Estrildidae are widespread and richly differentiated
in Africa, the Oriental Region and Australia, whereas the Ploceidae were successful
only in Africa. The sunbirds (Nectariniidae) have successfully colonized the wide
area from Africa to New Guinea, while the honey-eaters (Meliphagidae), so rich
in species in the Australo-Papuan region, did not enter the Sunda Islands. The
analysis of such differences has not yet progressed very far.
Continental drift is known to have occurred which, however, does not mean that
we can or must explain all distribution patterns in terms of drift. Mayr (1972h)
discussed faunal relations consistent with classical land bridge interpretations
(Bering Straits bridge, Panama bridge, the relations between the Oriental and
Australo-Papuan faunas). Other faunal relations are best explained by the theory
of continental drift (e.g., North America–Europe).
Mayr was a prominent representative of the “Center of origin concept” or “Dispersal
paradigm” whose basic tenets are: (1) Many animal groups differentiated in
well-circumscribed regions of the world (e.g., marsupials in Australia); (2) some