the inclusion of soft fruit, nectar or pollen in their diets requires no
real morphological or physiological adaptations. Moreover, fruit,
nectar, and pollen have high energy contents, with caloric values
close to those of animal-derived prey, and the added advantages that
they don’t move, or fight back!
Even when lizards have been observed to consume nectar or fruits,
this does not conclusively demonstrate any role as pollinators and
seed dispersers. Conversely, they may have negative impacts on plant
fitness by stealing nectar and fruit resources with no reciprocation in
enhancing reproduction of the plant, and moreover, reducing the
‘rewards’ for legitimate pollinators or seed dispersers. For a flower
visitor to act as a pollinator it must: 1) have pollen that adheres to its
body by coming into contact with pollen-bearing anthers; 2) travel to
another flower of the same species (in particular, on a different plant
to ensure cross-pollination); and 3) have the body region where
pollen had adhered to make contact with the stigma (the female
receptive organ) of the flower. An animal that consumes fruit will
only act as a effective seed dispersal agent if: 1) it consumes the
seeds; 2) they pass through its digestive tract whilst remaining
viable; 3) they are deposited away from the parent plant; and 4) the
seeds in the faeces are capable of successfully germinating.
Unfortunately, few studies do more than merely document that a
lizard species consumes nectar or fruit. Of the 211 instances of
frugivory, about two thirds of reports have shown that seeds are
present in the lizard’s scats, yet just only a quarter have determined
whether these seeds are viable/germinate, and only 16% have shown
that the lizards disperse the seeds. Of the 82 reports of nectivory, just
36.6% have recorded pollen adhering to the lizard’s body, and less
than 10% have actually demonstrated that the nectar-feeding
activities of the lizards result in pollination. Similarly, the quantitative
and qualitative contributions to plant reproductive fitness are rarely
measured, but there is evidence that lizards can be effective in both
pollination and seed dispersal.
Saurophily, Saurochory, and Island
Isolation.
Blue-tailed Day Gecko (Phelsuma cepediana)
in the Black River Gorges National Park in
Mauritius. Image by Dirkr.
In some cases lizards may act as only minor agents of pollination or seed dispersal; for example, novel observa-
tions of the typically insectivorous Pale-Lipped Shade Skink (Saproscincus spectabilis) acting as a legitimate
pollinator whilst feeding on nectar from Pollia crispata flowers in Australia’s rainforests. However, the
Mauritian Blue-tailed Day Gecko (Phelsuma cepediana) is the sole pollinator of a critically-endangered plant,
and vital to the ongoing persistence of this species; similarly, the Amazon Lava Lizard (Tropidurus torquatus) is
crucial to the seed dispersal and germination of a cactus endemic to Brazil (more below). Sometimes lizards can
be more effective than more conventional pollinators for plants with generalised pollination systems. For
example, on the island of Cabrera, the shrub Eurphorbia dendroides is visited by both insects (flies, bees and
wasps) as well as Lilford’s Wall Lizard (Podarcis lilfordi). A 1997 study found that that lizards were more
frequent visitors, carried greater pollen loads, and foraged for longer durations than insects, and this translated
into better pollination: at sites where lizards were abundant, fruit and seed set were significantly greater.