Sun bears, Ursus malayanus, are the
smallest of the bear species. They
probably evolved in Southeast Asia from the main lineage of bears about
one million years after the sloth bear line branched off.
It is likely that ancestral populations became isolated on the
Malay Peninsula or perhaps on one of the larger islands such as Sumatra
or Borneo during periods of higher sea levels during the Pliocene epoch
about 5 million years ago. The
ancestors of all the Ursine bears were relatively small.
The lineage that produced the sun bear produced a larger
ancestor, and then the modern sun bear became small again.
The ancestral sub bears were able to exploit an environment that
contained a number of larger, more efficient predators such as tigers
and leopards, by climbing trees and specializing on plant foods,
particularly fruit, and insects. These
adaptations became more specialized as the sun bear evolved.
At the height of their distribution sun bears ranged throughout most of
southeast Asia, and may have inhabited most of the islands west of
Wallace’s line at one time or another.
Wallace’s line lies between the islands of Bali and Lombok,
separates Borneo from Sulawesi (Celebes), and divides the Phillipines;
it marks the edge of the continental shelf.
East of the continental shelf the ocean becomes deep; so deep
that even during the coldest ice ages (and the lowest sea levels) there
was no dry land connection. On
the continental shelf itself, many of the islands became connected to
each other and to the mainland during periods of low sea level.
Sun bears were evidently able to colonize some of the islands of
the continental shelf and survive there, but they never made it across
the thirty or so kilometers of deep water to the oceanic islands as far
as we know. There are no
fossil records of sun bears from the oceanic islands but that could just
be due to limited opportunities to search for them.
Sun bears today face their greatest threats from habitat loss and
poaching. They have
traditionally been hunted by indigenous peoples, and most longhouses in
the Borneo rainforest contain a bear hide, but there was no significant
impact on populations from traditional uses.
Poaching has become an increasing threat.
The increase throughout Asia in trade of bear parts for medicinal
purposes, and the high monetary value of those parts, has greatly
reduced sun bear populations. They
are also captured and sold as pets throughout southeast Asia.
Wild pets are a prized status symbol in many Asian cultures where
rich and poor alike may wish to display a wild animal.
As the bears grow large and more difficult to manage they are
often sold to restaurants, traders, wildlife markets, bear farms or to
the bear equivalent of the glue factory where they are killed for their
valuable parts; paws for food, gall bladders for medicine, etc.
Although
there may be a few exceptions, the primary factor limiting the
distribution of sun bears is the presence of human beings.
Increasing human settlements, an increase in logging activity,
the development of plantations, and oil and gas activity with
accompanying roads are all reducing the amount of habitat that bears can
use. Military conflicts in
many parts of the sun bear’s range have undoubtedly had an impact and
increased the availability of firearms.
It is important to determine their status and distribution more
accurately and to protect critical habitat.
In many instances it may be possible to re-connect some of the
fragmented habitat that remains and some efforts are currently underway
(to maintain biodiversity, not just sun bears) in places like Vietnam.
Picture courtesy of
Harriet
Corbett,
Rox Graphics,
866 Rd. 7RP, Powell, WY 82435, 307 645 3202, crowhart@wtp.net
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