Geckos tend to
be small and rather defenseless lizards. They have the ability to shed their
tail, or tear their skin to escape a predator. And, while a few large species
may deliver a nasty bite, smaller species cannot. Geckos also seem to lack
chemical defenses to repel potential predators and therefore they rely on
avoiding predators by detecting their odor, or through cryptic coloration or
habits, or by distracting potential predators with their tails. Several recent papers describe ways in which some geckos avoid being
eaten.
The Australia,
nocturnal, rock-dwelling Velvet Gecko, Oedura
lesueurii, lives in the same habitat with centipedes. Pike et al. used a
combination of field data and laboratory experiments to determine whether a
predatory and venomous centipede (Scolopendridae: Cormocephalus sp.) influences habitat selection by this gecko. In
the field, they found centipedes and geckos were syntopic, used crevices
beneath rocks with similar physical dimensions, thermal regimes and degree of
sun exposure. Not surprisingly, geckos rarely shared rocks with centipedes in
the field. In laboratory trials, both geckos and centipedes selected shelters
with narrow rather than wide crevices and the presence of a centipede caused
juvenile geckos to avoid those hiding places. However, adult geckos continued
to select narrow crevices even if these contained centipedes. When the
experimenters added centipedes to narrow crevices beneath small and large rocks
occupied by geckos, both juvenile and adult geckos exited the crevice,
especially if it was under a small rock rather than large rock. Thus,
centipedes influence habitat selection by velvet geckos, and anti-predator behaviors
of geckos are both size- and context-dependent. In a related project, Webb et
al. (2010) tested the responses of the Velvet Gecko to the odors of two snake
species. One species, the Broad-headed Snake, Hoplocephalus bungaroides, feeds on geckos (therefore is
dangerous), the other, the Small-eyed Snake, Cryptophis nigrescens, feeds on skinks, but not geckos (less
dangerous). The authors tested whether predator avoidance by prey was modulated
by thermal costs associated with retreat-site selection and in both the
presence and absence of thermal costs, Velvet Geckos avoided crevices scented
by both dangerous and less dangerous snake species. Their results suggest that
Velvet Geckos treat both snake predators as equally dangerous. They repeated
the experiments in the field and obtained similar results, the geckos avoided
crevices that were temperature - friendly but scented with the odor of snakes-
regardless of whether or not the snakes were considered dangerous by the
researchers. Suggesting, the Velvet Gecko treats both snakes as dangerous and
avoids them.
Alonso et al.
(2010) examined the behavior of the Yellow-headed Gecko, Gonatodes albogularis, towards humans (the predators) in three
habitats near Bogotá in Colombia. They collected data on the tail display as an
observer approached the lizard. During transects geckos were approached by the
observer in a standardized way, and details of their tail-waving displays were
recorded. In control recordings animals were watched from a distant site
without approaching them. Their results showed sexual differences in
tail-waving. Male geckos waved their tails more frequently than females. But
they found no significant differences between male and female flight distances,
nor height above the substrate when the lizards were initially located. Males
displayed more frequently than females when approached than when the simulated
predator remained stationary. The authors suggest the display functions as a
pursuit-deterrent signal to potential predators; but note that some tail
displays were performed in the presence of conspecifics, therefore the display
may also have a social function.
In southwestern
Africa, Higham and Russell (2010) examined how two related species of Namib Day
Geckos of the genus Rhoptropus runaway from predators. Rhoptropus
afer and Rhoptropus bradfieldi are found in the coastal desert
regions of Namibia, and while R. afer commonly runs on sandy substrates
and moves between isolated sheets of rock, R. bradfieldi lives and runs
on isolated boulders. The morphology of the two species is quiet divergent. The
authors recorded the inclination of the substrates, quantified the maximum speed
and acceleration of each species on a level track, and measured their seed and
acceleration during escapes in the field. They found that R. bradfieldi occupies
steeper surfaces than those occupied by R. afer. On the track and in
nature, R. afer runs faster than R. bradfieldi. Rhoptropus
afer commonly runs for more than 2 or 3 m to escape a predator, whereas R.
bradfieldi commonly runs shorter distances, often less than 50 cm during an
escape sprint. Higham and Russell concluded that: (1) R. afer attains
higher maximum speeds when escaping under controlled and field conditions,
although the magnitude differs between conditions; and (2) hindlimb morphology
correlates with maximum running speed in R. afer, but not in R.
bradfieldi. They propose that these two gecko species represent distinct
and highly divergent ecomorphs.
Literature
Alonso, M. L.
B., J. M. Cotrina, D. A. Pardo, E. Font and M. Molina-Borja. 2010. Sex
differences in antipredator tail-waving displays of the diurnal yellow-headed
gecko Gonatodes albogularis from
tropical forests of Colombia. Journal of
Ethology, 28:305-311. DOI:
10.1007/s10164-009-0186-4
Higham, T. and
A. P. Russell. 2010. Divergence in locomotor performance, ecology, and
morphology between two sympatric sister species of desert-dwelling gecko. Biological Journal of the Linnean Society,
101:860–869.
Pike, D. A., B.
M. Croak, J. K. Webb, and R. Shine. 2010. Context-dependent avoidance of
predatory centipedes by nocturnal geckos (Oedura
lesueurii). Behavior,
147:397-412.
Webb, J. K., D.
A. Pike and R. Shine. 2010. Olfactory recognition of predators by nocturnal
lizards: safety outweighs thermal benefits. Behavioral Ecology, 21:72-77.