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which is subdivided into two series at the next level
of the hierarchy (Fig. 9.4). The wattsi seriescomprise
small brown lizards that perch within a few feet of
the ground. The bimaculatus seriescomprise large or
medium-sized green or grey-green lizards, which
are relatively arboreal. Islands (for which read
island banks) have either one species or two living in
the natural habitat, i.e. excluding small enclaves of
introduced anoles living near houses. Anguilla,
Antigua, and St Kitts are the island banks having
two species, in each case a larger bimaculatusand a
smallerwattsi.
Earlier research by Williams (1972, cited by
Roughgarden and Pacala 1989) had produced two
empirical ‘rules’ concerning the sizes and ratios of
the anoles:

1 Species from islands in which only one anole is
present are intermediate in size (snout–vent length)
between the body sizes seen on islands in which
two anole species coexist. This rule is correct for 11
of 12 island banks having a solitary species (they
range in length from 65 to 80 mm) and it applies
throughout the eastern Caribbean.

2 Species on a two-species island differ in body
length by a factor of 1.5–2.0, such that the larger
species exceeds 100 mm and the smaller is less than
or equal to 65 mm in length, the size of the smallest
solitary species. This rule is correct for four of the

five two-species island banks, and again applies

throughout the eastern Caribbean.

These patterns appeared to be consistent with the

character displacement model. It was also thought

that the original residents were members of the

bimaculatusseries, and that the invading species

were members of the wattsiseries, with both invad-

ing from Puerto Rico.

Although the character displacement mechanism

appeared to explain much of the variation in ano-

line lizards through the Lesser Antilles, there were

some exceptions and further research produced

more problems in respect to the northern islands

(Roughgarden and Pacala 1989):

●On St Maarten there are two anoles of nearly the

same body size. By the character displacement

hypothesis, one or both should be a new arrival.

However, both are differentiated (visibly and bio-

chemically) from other anoles in the region.

●Medium-sized lizards should become larger but

Pleistocene cave deposits demonstrated unequivo-

cally that larger anoles have become smaller, and

no fossil data show a medium-sized species becom-

ing larger.

●The two-species community supposedly has its

origins in two colonists of similar size, which

diverge in size. However, experimental studies of

216 EMERGENT MODELS OF ISLAND EVOLUTION

pogus

schwartzi

wattsi(2)

bimaculatus

leachi

sabanus

gingivinus

nubilus

lividus

marmoratus(9)

terraealtae(2)

ferreus

oculatus(4)

St. Maarten

St. Kitts Bank

Antigua Bank

Antigua Bank

St. Kitts Bank

Saba

St. Maarten Bank

Redonda

serieswattsi

bimaculatus series

Montserrat

Guadeloupe Bank

Illes de Saintes

Marie Galante

Dominica

Figure 9.4Phylogenetic tree for Anolisof the bimaculatus group (containing the wattsi series and the bimaculatus series) in the northern
Lesser Antilles. Those end-points represented by dots are monotypic species, the others are geographic races or subspecies according to current
nomenclature. This tree is merely one trunk of a larger phylogenetic tree for eastern Caribbean anolids, constructed on the basis of detailed
systematic/phylogenetic data by Roughgarden and Pacala (1989). (From Roughgarden and Pacala 1989, Fig.1.)