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widespread and abundant, contrary to the original
model. Ricklefs and Cox (1978) took this as illus-
trating that species on Jamaica have been able to
diverge sufficiently in ecological terms for these
generic-level endemics to avoid competition from
more recent colonists to the island. But is this a case
of special pleading? In addition, Pregill and Olson
argue that not all endemic species belong to groups
that were once widespread. Fossil data indicate that
some colonized an island from the mainland and
differentiated at the species level without having
dispersed to other islands, an example being the
Jamaican becard (Platypsaris niger). Similarly, they
argued that very similar distributional patterns can
arise from quite different evolutionary histories.

For example, the smooth-billed ani (Crotophaga ani)

is absent from fossil deposits in the West Indies,

whereas the white-crowned pigeon (Columba leuco-

cephala), a species that is practically endemic to the

West Indies but which, nonetheless, has a stage I

distribution like that of the ani, occurs commonly in

Pleistocene deposits.

Generally, analyses of faunal turnover in island

studies are based on the unstated premise that

environments are effectively stable, i.e. that biotic

forcing factors, and not environmental factors, are

responsible for turnover. In contrast, Pregill and

Olson’s (1981) analyses of the fossil record and of

relict distributions, particularly amongst the

xerophilic vertebrates of the Caribbean, indicated

THE TAXON CYCLE 213

Lesser

Antilles

1949

1931

1924 1936

1900

Early Stage I

Shiny cowbird

Late Stage I

Grey kingbird

Stage III – IV

House wren Adelaide warbler

1

2

Stage III

1

2

4

3

Stage II

Antillean bullfinch

1

(^32)
4
7
9
8
6
Figure 9.3The distribution of members of the Lesser Antillean avifauna, illustrative of the proposed stages of the taxon cycle. Species are as
follows: shiny cowbird,Molothrus bonairiensis; grey kingbird,Tyrannus dominicensus; Antillean bullfinch,Loxigilla noctis; house wren,Troglodytes
musculus; and Adelaide warbler,Dendroica adelaidae. The small figures indicate differentiated populations (subspecies). The house wren became
extinct on the islands marked* within the 20th century. Dates refer to first colonization. (Redrawn from Ricklefs and Cox 1972, Fig. 1.)