conveyed away from the parent plants, and may be
deposited in favourable or protected microclimates
(crevices or burrows, for example), or it may be that
successful dispersal is effected through sheer weight of
numbers. For example, of 160 scats collected from
Galapagos Land Iguanas (Conolophus subcristatus),
93% contained undamaged seeds, with a total of 5,705
seeds from 32 plant species. Although trials resulted in
only 4% of these seeds germinating, C. subcristatus’
large body size and long gut retention times means
that it is able to ingest large quantities of seed and
carry them considerable distances. This coupled with
its high local density means that C. subcristatus is an
effective, legitimate agent of seed dispersal. It is, in
fact, the sole disperser of endemic Jasminocereus
thouarsii, Scalesia affinis, Stylosanthes sympodialis and
Tephrosia cinerea, and appears to be important in
revegetating areas denuded following volcanic activity.
ble because in general there are very few instances in
which plants rely on the same agent to perform both
functions. Like most other cases of double-mutualisms,
the above relationship has evolved between two
endemic species in an ‘extreme’ habitat containing
with low animal diversity.
Highly Unusual Mutualists.
Returning for a moment to the Green Iguana (Iguana
iguana), this species has recently been shown to
practice a highly novel form of seed dispersal. All other
known seed dispersal by reptiles is via endozoochory:
fruits are ingested, and the seed is subsequently
dispersed when it is eventually deposited in scats.
Epizoochory involves dispersal in which seeds adhere
to the external surfaces of animals, and is common
amongst mammals and birds, whose fur and feathers,
In another instance of a lizard species assuming the
respectively, provide ideal surfaces to which seeds can
dual roles of both saurophily and saurochory, the
adhere. Reptiles’ smooth, scaly skin would seem to
Striped Lava Lizard (Tropidurus semitaeniatus) is both preclude this method of dispersal, however Green
the most important pollinator and seed dispersal agent Iguanas have been documented to effectively disperse
of the cactus Melocactus ernestii. Lizard pollination has seeds of Melocactus curvispinus which adhere to their
been found to result in a significant increase in fruit
snouts when they consume the fleshy fruits. Moreover,
set, and seeds that had passed through the lizards’
seeds stuck to the lizards’ snouts germinated in higher
digestive tracts exhibited a significantly enhanced
numbers and at faster rates than ingested seed and
germination rate. Lizard-plant mutualisms involving
those collected from fruits.
pollination and seed dispersal are all the more incredi-
Mexican Spiny-tailed Iguana (Ctenosaura pectinata)
eating leaves in a herb garden in Puerto Vallarta,
Mexico. Image by Jeremy Christensen.