Challenges for the protection of orangutans and their habitat
Vulnerability of orangutans Orangutans are extremely vulnerable to extinction due to a combination of factors: they have an exceptionally slow repro- ductive rate, they require vast areas of contiguous rainforest to live in, and they are very much restricted to lowland forest areas.
Sumatran orangutan females give birth to just one infant at a time, only every eight or nine years (Wich et al. 2009). As a direct consequence of this slow reproductive rate, orangu- tan populations are very susceptible to even very low levels of hunting. Indeed, the loss of as little as 1% of females each year through hunting or other unnatural causes of mortality can place a population on an irreversible trajectory to extinction (Marshall et al. 2009a).
For orangutan populations to be viable over the long term they need vast tracts of contiguous rainforest, at least 500 km2 (Marshall et al. 2009b). Tis is because orangutans tend to live at very low densities, as low as just one individual per km2
less in many areas, although densities can also reach as high as seven individuals per km2
in some parts of Sumatra (van
Schaik et al. 1995; Husson et al. 2009). But also because Suma- tran orangutans utilize very large home ranges. In some areas, a
single adult male may occupy a home range as large as 100 km2 or more (Singleton et al. 2009).
Finally, Sumatran orangutan populations are largely restricted to lowland rainforest (Rijksen and Meijaard 1999), with most Sumatran orangutans living below 500 m and rarely venturing higher than 1,500 m asl. Tese forests are most threatened by con- version to other land uses, particularly for agricultural expansion.
Orangutans are most threatened by forest loss which results from a combination of road development, expansion of large- scale agriculture, logging concessions, mining and small-scale encroachment. Tese threats can be directly attributed to in- adequate cross-sectoral land use planning, reflecting needs for short-term economic growth, and a lack of environmental law enforcement (Robertson and van Schaik 2001).
Forest loss From the time humans arrived on Sumatra approximately 40,000 years ago until very recently, the island was largely cov- ered in lush tropical rainforest (Cribb 2000). However, during the last two centuries most of the forests have been converted to other land uses, dominated by people. Forest loss in Sumatra is