Plants and animals interact in many ways, both mutually beneficial and antagonistic. The most important ways they can help each other are dispersal and pollination. Many examples can be found in Ridley (1930).
Dispersal
Dispersal is important for the pioneer belukar plants to be widely distributed and more successful in the secondary forests. The majority of belukar plants are dispersed by animals, especially birds and bats, which are highly mobile creatures. Many of the plants have edible fruits, which are consumed by the animals and then spread over a wide range when the animals excrete the seeds in their faeces. Belukar plants tend to flower and fruit at a young age, each fruit tends to have many seeds. For example, Chin (1970) reports that Melastoma has between 394-1472 seeds per fruit, while Adinandra has between 83-189. The seeds are also very light and small, e.g. Adinandra seeds are an average of 0.948 mg, those of Fagraea, 0.269 mg, etc. All these factors contribute to their ease of dispersal. Compared to the dipterocarps, as mentioned above, they make use of the mobility of animals to help them in dispersal. Hence, they can colonize newly abandoned land with great vigour.
Phua and Corlett (1989) report that the Lesser Short-nosed Fruit Bat, Cynopterus brachyotis, consumes a wide variety of fruits, including a significant number of the belukar plants, like Adinandra, Fagraea, Vitex pinnata, etc. Cynopterus tends to fly to the fruits, bite them from the tree, then fly away to another place to consume the flesh of the fruit and drop the seeds before flying back for more. Because of this behavior of the bat, the seeds are dispersed over a wider area than they would if the bats simply stay in place to consume the fruits.
Birds also feed on a wide variety of fruits. The Yellow Vented Bulbul feeds on Rhodamnia, Melastoma, Cinnamomum etc., while the Turtle Dove feeds on Melastoma, which Ridley (1930) said was "one of the first bushes to appear in the waste fields of lalang grass, where the seeds are dropped by pigeons and bulbuls." Bulbuls also tend to go after the seeds of Dillenia, perhaps attracted by the bright red colour of the arils. The successful exotic, Acacia auriculiformis, is also dispersed by birds, which are attracted to its seeds by the bright yellow arils. In fact, seeds of Melastoma germinate better after passing through the digestive tract of a bird. (Chin, 1970)
In more mature secondary forests, monkeys are active dispersal agents, '"attacking vigorously" the fruits of Eugenia, Passiflora, etc. However, they are not commonly encountered on the Ridge, though a number were sighted a few years back and may or may not still be present. Finally, there is the interesting case of Ploiarium alternifolium, another pioneer plant, where the seed capsules dehisce (split) on the plant, and rain washes them down to be dispersed.
Pollination
Pollination is carried out by many insects. Turner notes that carpenter bees (Xylocopa latipes) can be seen pollinating Dillenia and Melastomain Singapore. In addition, the figs, Ficus spp. are famously pollinated by the tiny fig wasps, which lay their eggs in the figs. The eggs then hatch and the wasps mate. The males die and the females squeeze out of the fig to lay their eggs, and in the process pick up pollen. When they enter other figs to lay their eggs, they deposit the pollen and hence pollinate the figs.
Myrmecophytes
Macaranga triloba, the Mahang, is a plant that can be found in Adinandra belukar though more commonly in Trema belukar. It is a myrmecophyte, literally meaning an "ant plant". Its stem is hollow, as the pith within disintegrates just behind the meristem (growing tip). Within the hollow, ants of the species Crematogaster borneensis establish their colonies. Small holes along the stem can be seen where the ants enter and exit. The plant also provides small white food bodies for the ants to feed on. In return, the ants protect the plant against foreign invading insects and other small creatures. The ants also bite off the growing tips of plants that come near the Macaranga plant, hence preventing vines and other plants from growing over and smothering it.