[Taxacom] Monkey biogeography

Tue Jun 19 17:37:14 CDT 2018

To me when looking at these issues you need to do comparative tests. So the
primates do not cross into eastern asia-pacific and present there are
cuscus. Personally I do not see the relationship there. Or the relevance.
Why because there are many groups of species that do not cross the same
boundaries. Cryptodiran turtles are almost completely absent from
Australia, New Guinea etc but are present all the way to this dead zone
that many groups never crossed. Pleurodiran turtles are dominant in
Australia, New Guinea etc. In fact the only cryptodiran turtles east of
this zone are those that are salt tolerant, ie Trionychids and
Carettochelyds. It is also more or less the line of separation for many
placental mammals vs the marsupials. Many snakes, lizards, amphibians, fish
also do not get across this zone. There is certainly something happening
there. I do not think it is explainable by competition alone, or even
ecology. There is nothing in the ecology of eastern asia-pacific and
australia that prevents the thriving of cryptodiran turtles or the true
frogs. Nothing in south east asia that chelids could not survive. Feral
species show these groups can survive just fine. There are 10 species of
deer, 2 species of turtle, and 1 species of primate introduced in australia
(I think the primate was eventually wiped out but it did well for a long
time).

So what can get across, rodents, bats, birds, some snakes, some lizards,
but all in all it is fast movers and salt tolerant species. With cycling
climate over the milenia, including in recent times, the amount of land in
these aras between south east asia and australia has repeatedly been
reduced to almost nothing. Currents have changed directions many times.
Until Australia got to around 10 deg south (Cape York) the current off
south east asia went straight out into the pacific and off towards Venuatu.
You cannot look at this from the point of view of where all the land is
right now, where the currents go now. You need to look at the paleo data.

For me I do not think the primates could survive the crossings once you get
past Borneo which could only have landed them in New Guinea or Australia in
the last 20 million years, before that they would have ended up in the
Pacific Ocean for trying.

Its also to do with founder effects. One gravid tortoise can float in the
ocean for 6 months hit an island and give rise to a whole population. No
mammal could do this.

In other words I think we need to look in great detail at a bigger picture
to understand that region. I spent much of my career working on South East
Asian and Australasian species, mostly turtles. Much of their
distribuitions is to do with ocean currents, sea levels and tolerance for
some horrific conditions, at least long enough to make it to a safer zone.

Cheers Scott

On Tue, Jun 19, 2018 at 5:48 PM, John Grehan <calabar.john at gmail.com> wrote:

> 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.
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