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ResearchBlogging.orgThe genus Apomys (Philippine forest mice) is proposed to be divided into two subgenera: Apomys and Megapomys based on the findings of the Heaney expedition [1]. Megapomys includes A. abrae, A. datae, A. gracilirostris, A.sacobianusA. aurorae, A. banahao, A. brownorum, A. magnus, A minganensis, A. sierrae, and A. zambalensis. See previous post.

The discovery isn’t serendipitous.  The authors used predictive biogeographic models that are relevant to the Philippines in general and to  Luzon in particular to determine which places they will likely see some new species. These models factor “geographic features such as elevational patterns of distribution, elevation of mountains, degree of isolation of mountains among others.” Moreover, Heaney probably also tested some of his hypotheses which are currently emerging on the study of  island biogeography [2].

Where are the Megapomys (click for larger view)? (Replotted representative data from Heaney, L.R. et al, Fieldiana Life and Earth Sciences, Number 2:1-60. 2011)

In [1], they have concluded that the geographic distribution of the Megapomys are non random.  This means that patterns can be identified. The authors listed the following:

1. Species of Megapomys extend from northernmost Luzon to Mt. Banahaw, but no further south on Luzon.

The authors failed to capture any Megapomys in southern Luzon but they have captured small Apomys in the area. The mountains of southern Luzon are isolated from the mountains of northern Luzon by a relatively vast plain.

2. All of the species of Megapomys occur on Luzon only at elevations above 450 m, with few records below 800 m.

The species of Megapomys are animals of montane and mossy forest.

3. Each species of Megapomys is associated with a single mountain range or individual mountain that is isolated from other such mountains by lowland areas at 300 m or lower.

These mountains are like islands in the sea of plains.  For large mountain ranges, the species are as widespread, conversely for species of small mountain ranges. The only exception they found was with A. zambalensis but they said that this may be a clue to the movement of the Apomys across the mountains.

4. Two species of Megapomys occur on mountains over most of central and northern Luzon, although which species are present varies between mountain masses.

One species occurs from the lower limits of montane forest species while the other occurs from the beginning of prime mossy forest to the peak.

5. Species that occur within the same mountain mass are not sister-species and most often are rather distantly related.

The authors said that “Instead of close relatives occupying nearby localities in the same mountain region, they occupy similar elevations in different mountains.”

6. Megapomys diverge within particular portions of the elevational gradient throughout northern and central Luzon.

Moreover, the authors add that,

these patterns  imply a long history of  diversification within the subgenus Megapomys, with diversification processes that usually involved ecological (habitat and climate) and geographic (topographic and geological) components.

[1] Heaney, L., Balete, D., Rickart, E., Alviola, P., Duya, M., Duya, M., Veluz, M., VandeVrede, L., & Steppan, S. (2011). Chapter 1: Seven New Species and a New Subgenus of Forest Mice (Rodentia: Muridae: Apomys) from Luzon Island Fieldiana Life and Earth Sciences, 2, 1-60 DOI: 10.3158/2158-5520-2.1.1

[2] Heaney, L. (2007). Is a new paradigm emerging for oceanic island biogeography? Journal of Biogeography, 34 (5), 753-757 DOI: 10.1111/j.1365-2699.2007.01692.x