Primates: Gardeners of the Forest

“Gardeners of the forest: primate ecology and forest conservation” was the theme that the Primate Society of Great Britain chose to address for their 4th annual symposium, with Bristol Conservation and Science Foundation on December 1, 2011 at the Bristol Zoo Gardens where I have had the honor to be invited to give a talk on seed dispersal by Madagascar primates, the lemurs. This is a rough summary of the talks that have been presented by several professors and myself.

The first ecological process that comes in my mind when thinking about primates as gardeners is seed dispersal because the majority of frugivorous primates disperse seeds by transporting them through their guts or mouth pouch into another habitat, then “plant” the seeds where they will be able to grow. However, as Dr. I. Redmond stressed during the symposium, being a gardener is not only about planting seeds. Much like a gardener taking care of his garden, a non-human primate do so by cutting down some branches to create light gaps when they create their nests, participating in pollination, exterminating herbivorous insects by eating them as part of their diet, ….

Seed dispersal by non-human primates

Seed dispersal by primates has gained major interest in the field of primatology and tropical ecology, especially because the majority of tropical trees produce fruits that are adapted for animal-dispersal. Dr. D. Chivers highlighted the large network that gibbons create with a wide range of fruit species that they consume (both bird- and large mammals-fruit types), and their efficient role in seed dispersal and forest regeneration in the tropical forest of South-East Asia by swallowing and defecating intact seeds. In the tropical montane forest of Nyungwe National Park, Rwanda, chimpanzees also play a major role in dispersing large-seeded tree species through spitting “wadge”, which contains seeds, with their prehensile lip.

Unfortunately, the majority of large-bodied frugivorous fauna including primates are facing critical threats from deforestation, habitat degradation and hunting. The ecosystem consequences of hunting pressures have been discussed in depth by Prof. C. Peres by simulating the probability dispersion of seeds if the large-bodied frugivores are eliminated across Amazonian forest.

Does primate seed dispersal matters in Madagascar?

Madagascar stands among the hottest hotspots in the world with a highly diverse and speciose plant population, endemic fauna and flora, but with increasingly degraded ecosystem. However, the island lacks fruit-eating mammalian assemblages, which would make the Malagasy primates more important as seed dispersers than in any other tropical regions. In his talk on revisiting the role of primates as seed dispersers, Prof. J. Ganzhorn has raised some points to review the over-rated role of Malagasy primates as dispersers, for instance the non-existence of apparent evidence of co-evolution between lemurs and the fruiting plant traits while Madagascar forest ecosystem have evolved in isolation, the existence of tree species with large-sized seeds despite the absence of large frugivores in the area, the disappearance of lemurs in parallel with rodents’ which have potential effects on forest regeneration.  While I do not dispute these points, I do not fully agree with all of these either. Frugivorous lemurs do contribute effectively in seed dispersal by transporting them into suitable environments increasing plant reproductive success. There are indeed some ecological conditions, biotic and abiotic, that prevent seeds from establishing like light gaps. My study in Ranomafana National Park, Madagascar showed that although there are few gaps in the forest, lemurs deposit majority of seeds into these openings which is good for seed-to-seedling recruitment and survival for most tropical plant species. Tree species may sometimes have clumped distribution regardless of the dispersal agent as Prof. J. Ganzhorn stated, but in a forest without lemurs there may be more clumping of seedling distribution as the majority will be dropped under parent tree, and may not even survive because of density-dependent mortality. We both agreed that such research is much needed for the future of lemur ecology.

Primate conservation

As I stated earlier, the majority of primates are facing critical threats into extinction. One of the most alarming event that causes such threats are direct anthropogenic pressures through extensive deforestation, and human induced-climate change by “converting carbon sinks into carbon source” as the case of the forest in China, according to Dr. H. Chatterjee. She then predicts the future effects of human-induced climate change on these threatened primates using data form past and present. Primate future distributions have also been examined by Dr. A. Korstjens. Dr. S.Cheyne emphasized the effects of habitat fragmentation on Asian ape population and discussed the efforts that have been done to preserve these species, and to degraded areas around forest edge by using rope-bridge to encourage the movement of apes between fragments to disperse seeds. Habitat loss can also affect the ranging behavior and foraging efficiency of primates as in the case of grey-cheeked mangabeys, a study by Dr. K. Janmaat, because they lack long-term spatio-temporal memories.

For the majority of primate species, the threats on their population lay in the loss of essential food resource, as the case for the chimpanzees of the Budongo forest in western Uganda. Prof. V. Reynolds explained how the increasing use of raffia palm tree leaves by tobacco farmers have lead into the destruction of chimp’s main source of sodium, and discussed the efforts being conducted between different stakeholders to resolve the issue, and to conserve both primates and the forests whithout neglecting the need of the famers and the interest of each party.

To find out more: http://www.psgb.org/Meetings/Winter2011.htm

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