Sunday, July 3, 2011

Varanus Indicus Populations In Asia

Currently, the Varanus Indicus species group is, despite the efforts of several workers, quite possibly the least resolved group of varanoid lizards in the world. They occupy a vast and difficult to access geographical region from the Solomon Islands in the east, across New Guinea with its shelf islands and parts of northern Australia, through the Moluccas as far as Talaud in the northwest, as well as some remote Pacific Island groups.

This is a region of unparalleled complex geological history consisting of thousands of variously sized islands where isolation and other evolutionary forces have driven populations to diverge and differentiate, resulting in a phylogenetic and ecological diversity that is still poorly understood.

Varanus Indicus

The Moluccan islands (Maluku) of east Indonesia forms part of the biogeographical region known as Wallacea. Traditionally considered a transition zone between the Australian and Asian faunas, many of the
islands also hold a considerable number of endemic species and have at least for some animal groups played
an important role in speciation processes (How and Kitchener, 1997, Ziegler et al., 2007b).

The number of identified species in the Varanus indicus species group in the Moluccas has risen from one to eight during the last decade (of which seven are endemic to this region), and more will inevitably be described. Sweet and Pianka (2007) review the reasons for the high diversity of small monitors (less than 130 cm total length) east of Wallace´s Line, concluding that the historical absence of predatory placental mammals has played a fundamental role in the radiation of lineages such as Euprepiosaurus.

The numerous islands with their different communities provide the ideal natural experiment to study resource partitioning and ecological release in monitors. Since studies on varanid communities have historically been largely restricted to dry and seasonally wet Australian environments, it seemed relevant to compare these “dry communities” with ones in the wet tropics, such as in the Moluccas. It is particularly interesting since most of the species within Moluccan communities are very similar in size and more closely related than within most Australian communities (where assemblies include species of several subgenera).

Varanus Indicus

Despite the recent discovery boom of new species, there has been very little fieldwork involved, and all the descriptions, except for V. lirungensis Koch et al. (2009), have been based solely on museum or animal trade specimens. The first ecological observations of many of these species were made during this study on three separate field trips in 2008 and 2009. This paper concerns varanids of the larger islands of the biogeographical northern Moluccas: Halmahera, Morotai, Bacan, Kasiruta, Gebe and Obi. The Sula
Islands are also included in the administrative unit, but group biogeographically with Sulawesi and are not
considered further here.

Varanus Indicus

 Field work was conducted during March 2008, December-February 2008-2009, mid April- mid June,
and late October-mid November 2009. Investigations were made in coastal habitats (Fig.4), lowland forests swamps, and hill forests on Halmahera, Bacan, Morotai, Gebe and Obi. These are all climatologically rather similar and are, or have historically been, covered primarily by tropical rainand evergreen forest. At present, much of the lowland forests are degraded, converted to plantations or even mined for minerals. Annual rainfall varies according to land topography, but averages between 1500 and 2000 mm. (Monk et al., 1997; Bacan Agricultural University, pers. comm. 2009), and lowland temperatures are 25-30 oC year-round. December through March tends to receive the heaviest rainfall, but most of the Moluccas rarely experience prolonged dry periods.

Many of the V. indicus group monitors can be observed by searching on foot in suitable habitats. Alternatively, some of the shyer species can be attracted to bait (fish/meat). Varanus yuwonoi is particularly difficult to observe, and the author was forced to follow a professional animal collector at work in order to see this species at all. Locating monitor lizards in tropical wet forests presents particular difficulties since it
excludes the possibility of using tracks as aid and the dense vegetation provides ample cover and places to
hide. Recurrent periods of rain and clouds often decrease activity levels of the animals, making observations
difficult for days or weeks on end. For each observation, a set of data (most importantly: habitat use, location and activity etc.) were recorded. In a few cases, dead animals were encountered and stomach content and reproductive condition was analyzed.


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