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58 IGUANA  •  VOLUME 15, NUMBER 1  •  MARCH 2008 NATURAL HISTORY RESEARCH REPORTS

Trophic Ecology 
of a Spiny-Tailed Iguana

Animals respond to changes in food
quality, resource availability, and patterns
of food dispersion by modifying foraging
behaviors. In species such as the 
Cape Spiny-tailed Iguana (Ctenosaura
hemilopha), predation pressure also may
affect escape behavior, habitat use, and
foraging behavior. BLÁZQUEZ ET AL.
(2007. Biotropica 39: 496–501) studied
the diet of adult spiny-tailed iguanas in
the desert of southern Baja California.
Their goals were to determine if spiny-
tailed iguanas behave as food generalists
or specialists, to evaluate the role of igua-
nas in seed dispersion, and to evaluate
whether iguanas modify their diets as a
function of predation risk.

Iguanas consumed mostly plants,
consuming at least 22 of the 83 species
occurring in the study area. The main-
stay of their year-round diet consists of
the leaves of three legumes, as well as
flowers and fruit when available. Spiny-
tailed Iguanas use leafy trees, such as P.
articulate and L. candida, and the selec-
tion of those trees as habitat allows them
to access food and refuges at the same
location, reducing predation risk.
Although iguanas could move around to
feed, they rarely did. Intense predation
by raptors and mammals may be the
strongest factor influencing iguana for-
aging behavior.

Genetic Variation in Introduced 
Anolis Lizard Populations

Invasive species usually are established
with a small number of founders, and
therefore are expected to have relatively
low genetic diversity. Even when num-
bers increase, reduced within-population
genetic variation is expected when com-
pared to the native range. The increased
relatedness among individuals can cause
inbreeding depression, limiting popula-
tion growth and increasing the probabil-
ity of extinction of a population. In con-
trast, some recent studies have shown
that invasive populations can have higher
genetic variation than native populations
and experience rapid evolution because
they are formed by multiple introduc-
tions from different portions of the
species’ native range.

Recently, KOLBE ET AL. (2007.
Conservation Biology 21: 1612–1625)
used mitochondrial DNA sequence data
to examine the molecular genetics of ten
introduced populations belonging to
eight species of Anolis lizards. Evidence
indicates that 80% of Anolis lizard intro-
ductions originated from multiple source
populations. Seven of eight introduced
species of Anolis in Florida were derived
from multiple native-range sources, and
one of two introductions to the
Dominican Republic had multiple
sources. The results suggest that multiple
introductions from several sources, fol-
lowed by admixture, is the norm rather
than the exception in this genus.

Gila Monsters in California
The Gila Monster (Heloderma suspec-
tum), widely distributed in parts of the
Mojave, Sonoran, and Chihuahuan
deserts of the southwestern United
States and northwestern Mexico, is rare
in California. Habitat in which the
species has been observed in California
is characterized by rocky, deeply incised

topography, in most cases associated
with large and relatively high mountain
ranges. Most localities are in riparian
areas (including the lower Colorado
River) and range from near sea level to
over 1,200 m. All records except one
(Mojave River) occur east of about 116°
longitude. The distribution of the
species in California suggests an invasion
into the high mountain ranges of the
northeastern Mojave during the last
interglacial via the Colorado River cor-
ridor. LOVICH AND BEAMAN (2007.
Bulletin of the Southern California
Academy of Sciences 106: 39–58)
explored the hypothesis that climate pat-
terns shaped the current distribution of
the Gila Monster in California. Warm
season precipitation data from recording
stations closest to Gila Monster localities
are almost identical for those in western
Arizona, where the species is more com-
mon. Summer precipitation may be
important in the foraging ecology of the
species. Gila Monsters were probably
already rare in California long before the
arrival of Europeans due to changes in
climate and landforms that delimited
the marginal location of California in
the range of this species. Fortunately,
most of the habitat for this species in
California is protected or relatively free
from human disturbance.

Most Gila Monster (Heloderma suspectum)
habitat in California is protected or relatively
free from human disturbance.

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Seven of eight introduced species of Anolis in
Florida, including A. distichus (illustrated
here), were derived from multiple native-
range sources.

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N A T U R A L  H I S T O R Y  R E S E A R C H  R E P O R T S

Although Cape Spiny-tailed Iguanas
(Ctenosaura hemilopha) can move around to
feed, they rarely do.

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