meridionalis) and the Common Kestrel (Falco tinnuncu-
lus). Moreover, shrikes and kestrels have different
habitat preferences, so this combination of direct and
indirect dispersal ensures seeds are deposited in a
variety of environments. Researchers found that seeds
were present in just 7.3% of G. atlantica droppings, but
31% of kestrel pellets, and over 55.7% of shrike
regurgitations. The percentage of viable seeds,
percentage germination and germination rate were all
highest from shrike regurgitations, followed by lizard
scats, but significantly lower in kestrel pellets. So
whilst ‘secondary’ dispersal is enhanced by the
shrikes, kestrel predation has an overall negative net
effect, since it entails both the consumption of
legitimate direct seed dispersal agents (the lizards)
and reduced germination of seeds acquired from their
lizard prey.The Noronha Skink (Galliotta atlantica) consumes
fruits of the plant Lycium intricatum, and is in turn
eaten by the Great Grey Shrike (Lanius excubitor).
Image by Simone Giachello.2 x qtr page adsAnother indirect form of seed dispersal involving
lizards and birds occurs on the island of Santa Fe, in
the Galapagos Islands archipelago. The Santa Fe Land
Iguana (Conolophus pallidus) relishes fruits of the
cactus Opuntia ochios var. barringtonensis, consuming
them as soon as they fall to the ground. The seeds are
ejected when the iguanas chomp on the fleshy pulp,
and are then picked up and subsequently dispersed by
the Galapagos Mockingbird (Mimus parvulus).Ancient Niche Expansion.Saurophily and saurochory appear to evolve in
environments where there are few insects (a potential
source of both food for lizards, and pollinators for
plants), and high densities of lizards, which encour-
ages these species to expand their dietary niche to
reduce competition. These conditions are especially
common on islands, which are typically difficult for
mammals to colonise due to their isolation and limited
resources. Free of mammalian predators, this allows
lizards to reach far higher abundance, and in the
absence of large mammalian herbivores, these reptiles
are able to include fruits in their diet and fulfil the role
of seed dispersers.Birds, although highly mobile, are endotherms, like
mammals, and have relatively high energy and water
requirements compared with lizards. Thus they are
also often at lower abundances on islands, again
leaving the frugivorous niche open to lizards.
Additionally, the isolation of many island environ-
ments means that insects may be at relatively low
abundances, forcing typically insectivorous lizards to
consume nectar, pollen and fruit. Indeed, across
several populations of Podarcis spp., lower arthropod
diversity and availability was found to be associated
with greater consumption of plant material.
Researchers have also noted the predominance of
insular (island) species amongst those lizards known
to feed on nectar and fruits.Because lizards are typically territorial and have
relatively lower mobility, they may not be as effective
pollinators as flying insects and birds, particularly
since if they visit flowers on the same plant, or
adjacent ones, this can result in inbreeding. Similarly,
the distance over which seeds are dispersed by lizards
has been rarely evaluated, and is likely to be less than
many other vertebrate seed dispersers. Nevertheless,
studies have documented that larger lizards, in
particular, may roam over considerable distances and(^)
Santa Fe Land Iguanas (Conolophus pallidus) cannot
resist the fruit of the cactus Opuntia ochios var.
barringtonensis. Image by marktucan.
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