• Alex Taylor

Starving to Extinction

Climate change threatens biodiversity in subtle and complex ways, and can have a particular impact on extreme feeding specialists. As it causes Madagascar’s dry season to get longer and longer, endangered greater bamboo lemurs may be forced to eat less nutritious food, and could slowly starve.

The greater bamboo lemur, staring starvation in the face

Madagascar is the home of its famous and fascinating lemurs. One such lemur is the greater bamboo lemur, once broadly distributed across the island, but now is one of the most endangered primates on earth. Habitat destruction is the biggest threat to lemurs, and this is the main cause of the greater bamboo lemur’s status. However, climate change is set to endangered them even further, in ways that highlight just how subtle and complex its effects can be.

Greater bamboo lemurs are, as their name suggests, extreme feeding specialists. And not just on bamboo, on a single species of bamboo, almost to the exclusion of all others. They prefer to feed on the most nutritious parts of the bamboo, the tender ground shoots. Birth and weaning seasons are timed for peak bamboo shoot availability which is during the rainy season, when rainfall exceeds 250mm per month. However, during the dry season, these shoots are not available so they make a switch. Between August and November the lemurs are forced to feed on less nutritious woody trunk. Know as culm, the greater bamboo lemur need to use their specialised teeth to gnaw on it. It is so “mechanically demanding” that juveniles cannot break it, relying on adults to obtain the softer inner parts for them.

The worry for conservationists is that climate change will cause the dry season in Madagascar to last for a longer time than it does now. This would mean less time for the lemurs to feed on the more nutritious shoots, and longer for them to try to survive on the less nutritious culm. The greater bamboo lemur may starve to extinction.

A study based on 2,387 feeding observations in Madagascar’s Ranomafana National Park documented this. Analysis of the lemur’s current (highly restricted) distribution compared to their past one showed that they are found only in the parts of the island that has the shortest dry season. It appears that a short dry season, with less than 50mm rainfall, has been crucial to their survival in the past.

The scientists also examined climate models, which gave bad news. They suggest that the areas the lemurs inhabit now are the areas that are likely to experience longer and longer dry seasons in the future, due to climate change. The lemurs in these areas are projected to live with rainfall patterns that are similar to those in regions in which lemurs have gone extinct in the past as the environment dried.

These findings may also have implications for other bamboo specialists, such as the most famous of all bamboo munchers the giant panda, as well as the red panda and another Madagascan lemur, the golden bamboo lemur. All bamboo eaters have a preference for the wet season’s high quality shoots, so the extended dry seasons could very well affect them in the same way. This is troubling given that both panda species are under threat, with much diminished ranges, and the golden bamboo lemur is also critically endangered.

Not only will they experience nutritional deficiencies, their teeth may suffer too. Bamboo specialists have physiological adaptations to cope with the tough food they eat, for example they can cope with the chemical defences of bamboo and have low daily energy expenditure. In addition, their teeth are well equipped to deal with bamboo…but they are not used to eating dry bamboo for so long. Giant pandas have already been shown to experience tooth wear and dead pandas have been found with their teeth in poor condition. An increase in tooth wear in greater bamboo lemurs will likely occur too, leading to loss in dental function and additional feeding difficulties.

Specialist feeders thrive where abundant food is available. However, the insidious threat of climate change may now cause it to become their downfall. Already threatened by habitat destruction, greater bamboo lemurs face a new threat, one extremely challenging to shield them from. Extended dry seasons will affect populations both within and out with protected areas - simply protecting their existing habitats will not be enough to guarantee their survival.

Feeding specialists are extremely useful to conservationists, as they can show us the intricate, hidden ways that climate change will impact endangered species. It is vital that we study them now. If we don’t, they may go extinct before we know all the reasons why. And that would make it so much harder to protect what remains.

#climatechange #primates #madagascar