iHerp_Australia_-_November_-_December_2018

Island fauna tend to be very vulnerable to extinction,
and the key role that lizards have as pollinators and
seed dispersers in many island ecosystems under-
scores the importance of protecting these species, for
their loss may also lead to cascading extinctions of the
plants they interacted with, and in turn, other animals
that also interacted with these plants. Already we have
lost forever the only two
gecko species endemic to
Rodrigues Island and
surrounding islets, both of
which were observed to
feed on fruits and nectar.
The geckos were ravaged
by habitat loss and
introduced cats and rats
following human colonisation of the islands in the late
19 th century. Early explorers’ descriptions noted the
common phenomenon of extreme tameness that
characterises many islands species in the absence of
larger predators, and this no doubt contributed to
their demise. The Rodrigues Giant Day Gecko
(Phelsuma gigas) - the largest of all known geckos, at

40cm in length – was eradicated in 1840, and the

Rodrigues Day Gecko (P. edwardnewtoni) became

extinct in about 1920. To restore the lost mutualisms,

there are proposals to introduce another large extant

Phelsuma species, the Round Island Day Gecko

(P. guentheri). Not only will this create an insurance

population (with Rodrigues Island now being rat-free)

for this endangered gecko,

which is currently

restricted to a single area

less than 2km^2 , but in

addition, it may restore the

interactions its congeners

performed in pollinating

and dispersing the seeds of

Rodrigues’ flora.

Another island mutualism under threat is that

between Lilford’s Wall Lizard (Podarcis lilfordi) and

Daphne Rodriguez, a threatened shrub endemic to

Menorca Island and Colom Islet. Its seeds are

dispersed solely by P. lilfordi, which is in turn

endangered, and extinct from Mallorca and Menorca,

2 x qtr page ads

‘The loss of lizard pollinators

and seed dispersers may lead to

CASCADING EXTINCTIONS

of other organisms.’

likely due to exotic predators. Consequently, this lizard

• plant mutualism is now restricted to the tiny Colom
  Islet, where P. lilfordi remains abundant. The lizards
  consume large numbers of D. Rodriguez fruits, which
  pass through their digestive tract and are eventually
  deposited in scats to germinate at some distance from
  parent plants. Seedling recruitment on Colom Islet is
  much higher than Menorca, where the lizards are
  absent and those seeds that do germinate are almost
  exclusively located under the parent plants, which is

detrimental to establishment and has led to a

reduction in genetic diversity.

Similarly, Cneorum tricoccon is another plant that

exists on a number of the Balearic Islands, on some of

which Lilford’s Wall Lizard and the Ibiza Wall Lizard

(Podarcis pityusensis) are present; on others the

lizards have been extirpated following the introduc-

tion of carnivorous mammals. Although two of these -

namely the Pine Marten (Martes martes) and the

Lilford’s Wall Lizard (Podarcis lilfordi) is the

sole agent of dispersal for seeds of a rare

shrub. Image by Ernesto Ochoa.

The Ibiza Wall Lizard (Podarcis pityusensis)

also performs an important role in seed

dispersal. Image by Andi111.