FSD 2010 - Monitor Lizard

5th International Symposium-Workshop on Frugivores and Seed Dispersal (1985-2010)

Monitor Lizards are the Frugivores of the Month

The Varanus species

Monitor lizards also known as bayawak or goannas, genus Varanus, are members of the family Varanidae. Varanus is a group of largely carnivorous lizards which includes the largest living lizard, the Komodo dragon, and the crocodile monitor. Monitor lizards are generally large reptiles, although some can be as small as 12 centimeters in length. Most species are terrestrial, but arboreal and semi-aquatic monitors are also known. Almost all monitor lizards are carnivorous, although some Varanus species are also known to eat fruit. The frugivorous species are all endemic to the Philippines; Varanus olivaceus, V. mabitang and V. bitatawa. In the Philippines, Monitor lizards are under serious threat from habitat destruction.

The Butaan Project

The first study (Auffenberg 1988) of Butaan concluded that monitor lizards are :

specialist frugivores and molluscivore,
feed on very narrow range of fruits,
forage exclusively on the ground to collect perfectly ripe fruits
have very small activity areas
are absent from degraded forest

Frugivorous vertebrates tend to be able to fly (almost all are bats and birds) and so these lizards have a unique ecological role as highly specialized and relatively immobile fruit eaters.

Fruit eating monitors require foraging strategies that are unlike any other reptile. They require constant supplies of at least two types of fruits from within a very narrow range of types. Some of its food trees are very common but have unpredictable fruiting patterns, others are very rare or have a very short fruiting season. Individuals must develop spatial maps in order to remember the location of important food resources within a very complex forest environment.

(Photo Varanus olivaceus © www.mampam.com)

Benneth (2009) studied the diet of the butaan by finding its droppings on the forest floor, and use them to determine seasonal and spatial changes in diet and variation between years. In total he found almost 1000 fecal samples on Polillo Island, one of the largest samples for any single population of lizards, and was able to identify the critical food resources that the animals depend upon. He also studied the fate of seeds dispersed by the lizards to understand the effects of the butaan on forest structure and its importance as a seed disperser. In total, Bennett (2009) monitored trees for almost half a million hours and recorded visits to some trees over three years. Certain trees are critical to butaan survival and he was able to identify these resources and take steps to protect them. (Photo: Daniel Bennett at FSD2005, Brisbane, Australia. © P.-M. Forget)

Websites

Wikipedia Monitor lizards

The Butaan Project

Experts of Monitor Lizards

Poo lost for Science

Giant, fruit-eating monitor lizard discovered in the Philippines

Welton, L. J. et al. 2010. A spectacular new Philippine monitor lizard reveals a hidden biogeographic boundary and a novel flagship species for conservation. Biol. Lett. published online before print April 7, 2010.

References

Auffenberg, W. 1988. Gray's Monitor Lizard. University of Florida Press, Gainesville.

Bennett, D. 1998. Monitor Lizards: Natural History, Biology & Husbandry. Chimaira Bucnhandelsgesellschaf. 352 pages.

Bennett, Daniel. 2000. "Preliminary survey and status report for Varanus olivaceus on Polillo Island.". in Daniel Bennett (in English). Wildlife of Polillo Island, Philippines. University of Oxford - University of the Philippines at Los Banos Polillo '99 project. Final report. Glossop: Viper Press. pp. 174 pp.

Bennett, D. 2009. Ph. D. University of Leeds.

More references about Monitor Lizards at mampam