DISTRIBUTION
The authors placed emphasis on the importance of biogeography. A concept called the Pleistocene Aggregate Island Complex (PAIC) postulates that islands, or group of islands, surrounded by deep waters during the Pleistocene should have their own assemblage of species distinct from surrounding islands, based on the presumption that such deep waters would have prevented interisland species from crossing expanses on land exposed during the Ice Age. Presumably, ensuing isolation would have been enough a barrier to allow the evolution of distinct lineages.
Thus, when we take into account the distribution of varanids from the V. salvator complex within the Philippines, we see that Sulu has the enigmatic V. rasmusseni, V. cumingii is restricted only to Mindanao, V. nuchalis is distributed in the islands in the western Visayas, V. palawanensis occurs only on Palawan, and V. bangonorum is found on the islands of Mindoro and Semirara.
Still, the concept of PAIC can be somewhat questionable in some instances, as in the case of the striking V. samarensis, as the islands of Bohol, Leyte, Biliran, and Samar were previously connected to Mindanao during the last Ice Age, although it has been also postulated that the islands of Dinagat and Caraga would have served as a filter zone that barred the exchange of several species between Ice Age northern Mindanao (the eastern Visayas islands mentioned above) and southern Mindanao (the entirety of present-day Mindanao).
An even more abstruse instance is found in V. dalubhasa,
which the authors stated to be distributed in the Bicol region, extending north to the town of Real in Quezon; its overlap with the range of the morphologically very similar V. marmoratus wasn’t clear, both from the time of the paper’s publication and to this day. Varanus marmoratus is now understood to occupy the rest of Luzon, plus the island of Lubang near Occidental Mindoro, and the island groups of Babuyan and Batanes. However, consultation with a few of my photos of what I perceived to be V. marmoratus
from Laguna hinted at the possibility that V. dalubhasa,
or at least those monitors that showed traits of that species, may well be present on the province. But it may not be as simple in other parts of the province. Recently, monitor lizards captured in the town of Kalayaan in the same province, but which I subsequently released, exhibited characters that were supposed to fit both V. dalubhasa and V. bangonorum.
According to the 2014 paper by Welton et al, V. bangonorum possesses “necks with gular region with characteristic dark blotches, becoming more prominent posteriorly” while for V. dalubhasa, they stated “gular region with irregular spots, faint anteriorly but becoming prominent and dark along lateral margins just anterior to gular fold.” Necks of V. marmoratus, in comparison, are typically obscured by dark pigmentation consisting of minute speckling all throughout.