Tom McLaughlin Borneo Post 29 Apr 12;
HOW are seeds dispersed now that large animals – elephants and rhinoceroses – have been hunted from their ecological habitats? Will tapirs take their place?
Rhinoceroses were once plentiful throughout the Southeast Asian ecosystem. They consumed vast quantities of plants and seeds and moved from one area to another releasing seeds in their excrement, thus aiding in dispersal.
However, the demand for rhinos because of Chinese medicine claims has decimated the population to the point where they are now on the critically endangered list. Conservation efforts by governments have largely failed throughout the world.
Elephants were also responsible for the wide dispersal of seeds – eating and then leaving their excrement from one place to another. Their habitat has been decimated from hunting for ivory and the planting of plantations.
Accumulating evidence has demonstrated the understory of the forest has shown a dramatic reduction in fruit trees formerly dispersed by these gentle giants. The ecological cascade has affected many species in the food web.
Could the Malayan tapir, the third largest ruminant after these great beasts, replace these wonders for seed dispersal? There are a couple of things in their favour. None of their body parts are used in traditional medicine. Their meat is not favoured. Although an endangered species, their survival looks a bit brighter than for rhinos and elephants.
Malayan tapirs are usually about 1.8 metres long and weigh about 350kg. They are solitary animals and eat fallen fruits and twigs from the forest floor. Running into thick bushes is their defence from tigers – their major predator.
An experiment conducted at the Wildlife Reserves in Singapore made an attempt to answer whether the tapir could replace the rhino and elephant for seed dispersal. Nine plant species, seven from Southeast Asia, were fed to eight Malayan tapirs, seven of which were born in captivity.
The fruits, purchased at a local market, included mango, durian, cempedak, rambutan, mangosteen, tamarind, longan, Dillenia sp (locally known as air simpoh) and papaya. A known number of seed fruit were fed to the tapirs. For example, the rambutan has a large central seed and the number the tapirs ate were counted.
Five hours later, the tapir dung was collected and the seeds counted. The seeds were then planted in pots to see if they would germinate after a journey through the digestive system.
Large seeds (durian, cempedak and tamarind) failed to germinate. Very few mid-sized seeds did not survive the gut passage. In comparison, elephants defecated 75 per cent of ingested tamarind seeds where 65 per cent germinated in a similar experiment performed elsewhere.
The tapirs are picky eaters. They have a special aversion to durians. They spat out or dropped many seeds eating only the flesh. Elephants gobbled and gulped everything in a single swallow. The tapirs also found great difficulty with eating hard elephant apples although the researchers concede this could possibly be because they were captive and had not been exposed to the fruit.
The digestive system of tapirs and elephants could also be major factor. Because of their teeth, tapirs are much better in crushing seeds than elephants or rhinos. The gut passage time is much longer in tapirs than in the larger denizens allowing the digestive juices to work more effectively.
These preliminary conclusions suggests the tapir will not replace elephants and rhinos for seed dispersal. However, the authors suggest many more studies must be performed in order to assess the role played by other dispersing critters including bears and hornbills. They also relate there needs to be further studies on the digestive systems of all major participates in seed dispersal before any concrete conclusions can be reached.
As the world’s rainforests become more fragmented and will eventually become islands surrounded by agriculture and human living space, the management of these remaining areas needs to be fully understood. This first study of the role of tapirs and seed dispersal is an important step in saving the ecosystem that will be left.
For more read ‘Asian Tapirs Are No Elephants When It Comes To Seed Dispersal’ by Campos-Arceiz et al, Biotropica 44(2):220-227 2012.
All things bright and beautiful, all creatures great and small, all things wise and wonderful, the Lord God made them all.
