Author Nur Estya Rahman Title Niche differentiation and ecophysiological studies of Myristicaceae species in natural habitats in Singapore Institute Thesis (M.Sc.) (Life Sciences) National Institute of Education, Nanyang Technological University Year 2019 Abstract Tropical rainforest systems are known to house high biodiversity and rich species of flora and fauna. Various niche concept theories have been described in various studies to explain species co-existence and species undergo differentiation to co-exist by adopting different strategies of partitioning resources. This process of niche differentiation could possibly shape the forest community structure and functional traits. The divergence of functional traits of tropical forest tree species could be assessed from the species’ interactions to their fundamental and realized niches, and aid in understanding species’ ecophysiological links of their functional traits and physiology to resources such as light and water availability. Therefore, this thesis consists of exploring two major physiological components of selected species from the Myristicaceae family; (1) field ecophysiology and selected functional trait studies of Knema tree saplings at different study sites; and (2) greenhouse studies of seedlings of Knema globularia in response to light and drought stress. Trees of the Knema sp. are often found in the understorey where there is limited light passing through the canopy and this could infer their ecophysiological preference and physiological function. Interestingly, results from the field studies concluded that Knema globularia was able to tolerate high irradiances but not prolonged drought stress, as indicated from the statistically significant RWC values derived between individual trees. Knema laurina species are versatile in terms of distribution within different topographical regions where they are often found on slopes and ridges. Thus, K. laurina species may have possibly managed to counter water shortage via other coping strategies. Knema malayana species are able to tolerate increasing light irradiances possibly through photoprotective mechanisms as evidently shown by high carotenoid content levels and high non-phottochemical quenching (NPQ) rise observed in the chlorophyll (Chl) fluorescence analyses. xv In the greenhouse study, seedlings of K. globularia indicated tolerance to high irradiance only in the presence of sufficient water supply for the seedlings to maintain turgidity and integrity of their photosynthetic tissues as well as their downstream physiological responses in maintaining homeostasis. Amongst the well-watered treatmentsseedlings at PPFDs of 150 μmol m-2 s-1 and 300 μmol m-2 s-1 respectively, showed the most stable readings throughout the experimental period. Amongst the drought treatments, 150T was the most stable as drought stress symptoms were evident by Week 4. This was possibly attributed to the low PPFD of 150 μmol m-2 s-1, thereby prove that Knema globularia are shade plant species that thrive well in the understorey of tropical rainforests. Results from functional traits analysed in this study showed that functional traits are useful tools to comprehend ecophysiological links and species co-existence of closely related species relative to the physiological responses of tropical rainforest tree species such as the Knema sp. in the understorey. Today, it is critical to understand the interactions of tropical rainforest plant species such as the Myristicaceae species, a typical primary and late secondary rainforest indicator tree species, with the changing climate. xvi .