[Taxacom] Monkey biogeography

[John Grehan]

While one may have any kind of view about the origins of distribution for
primates in eastern Asia I thought it might be helpful for those curious
about the nature of biogeographic patterns (and especially for those who do
not have ready access to the literature) to see an excerpt below from Heads
(2012) on the eastern boundary. Note that this boundary is shared by other
taxa such as plants and birds, and the boundary involves taxa both to the
east and west. It is this commonality that may point to common historical
causes rather than chance ecological exclusions. But either way, the
biographic analysis identifies these commonalities as facts of biogeography
that have to be addressed by anyone investigating such matters.

John Grehan (apologies for any typos below)

Philippines-Sulawesi: Primates at their eastern limit

Apart from humans and human introductions, primates reach their eastern
limit at the Philippines, Sulawesi, and Timor (Brandon-Jones et al., 2004;
Figs. 3-1 and 5-15). Many other taxa have a similar distribution, as they
are widespread in the tropics but absent from subtle habitat in Australia,
New guinea, and the Pacific islands. For example, several angiosperm
families have a wide distribution in warmer America, Africa, and Asia, but
extend east only to Borneo (Peraceae, Gelsemiaceae, Anisophyllaceae; cf.
strepsirrhines) or to Sulawesi (Buxaceae, Erythropalaceae; cf. haplorhines)
(Stevens, 2010). The current absence of these groups from temperate regions
could be due to simple ecological factors, although their absence from
tropical Australasia is probably not. This absence could reflect an
ancestral absence or at least a low ancestral diversity in the latter
region.

Primate clades such as strepsirrhines range east to Makassar Strait, while
the eastern limit of primates and the main center of the tarsiers, one for
the group’s most distinctive clades, lie east of Sulawesi (Fig. 5-15). The
reason for any limit in the Indonesian archipelago is not obvious; primates
in the regions, such as Nasalis and Macaca, are excellent swimmers in
rivers and the sea (Nasalis individual have been picked up by fishing boats
some distance offshore). Despite this, Nasalis does not cross Makassar
Strait. This boundary does not seem to be related to potential means of
dispersal. The limit of all primates in eastern Sulawesi is even more
striking as the Moluccan Islands (Maluku) are so close. While primates
occur on the Banggai Islands (Tarsius pelengensis is endemic on Peleng
Island; Fig. 5-15), none has ever been recorded across Salue Timpaus Strait
(20 km wide) in the Sula Islands of the Moluccas. The strait is a minor
feature in terms of current geography but despite this it is a
biogeographic node of intercontinental significance. Primates and other
widespread groups reaching their eastern limit there are juxtaposed with
Australiasian taxa reaching their western limit at the same strait, for
example, the widespread passerine bird Monarcha (Heads, 2001; Fig. 16).
These precise eastern and western biogeographic limits and the high levels
of endemism on Sulawesi itself show no obvious relationship with current
geography or ecology and could instead be due to the earlier tectonic
history of the different component terranes.